7 CFR 1806.23 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-01-01

... other body of water as a result of erosion or undermining caused by waves or currents of water exceeding anticipated cyclical levels, or abnormally high tidal water or rising coastal waters resulting from severe storms, hurricanes, or tidal waves resulting from volcano eruptions or earthquakes. (g) Mudslide or...

Effect of subseabed salt domes on Tidal Residual currents in the Persian Gulf

NASA Astrophysics Data System (ADS)

Mashayekh Poul, Hossein; Backhaus, Jan; Dehghani, Ali; Huebner, Udo

2016-05-01

Geological studies in the Persian Gulf (PG) have revealed the existence of subseabed salt-domes. With suitable filtering of a high-resolution PG seabed topography, it is seen that the domes leave their signature in the seabed, i.e., numerous hills and valleys with amplitudes of several tens of meters and radii from a few up to tens of kilometers. It was suspected that the "shark skin" of the PG seabed may affect the tidal residual flow. The interaction of tidal dynamics and these obstacles was investigated in a nonlinear hydrodynamic numerical tidal model of the PG. The model was first used to characterize flow patterns of residual currents generated by a tidal wave passing over symmetric, elongated and tilted obstacles. Thereafter it was applied to the entire PG. The model was forced at its open boundary by the four dominant tidal constituents residing in the PG. Each tidal constituent was simulated separately. Results, i.e., tidal residual currents in the PG, as depicted by Lagrangian trajectories reveal a stationary flow that is very rich in eddies. Each eddy can be identified with a topographic obstacle. This confirms that the tidal residual flow field is strongly influenced by the nonlinear interaction of the tidal wave with the bottom relief which, in turn, is deformed by salt-domes beneath the seabed. Different areas of maximum residual current velocities are identified for major tidal constituents. The pattern of trajectories indicates the presence of two main cyclonic gyres and several adjacent gyres rotating in opposite directions and a strong coastal current in the northern PG.

The effects of tidal range on saltmarsh morphology

NASA Astrophysics Data System (ADS)

Goodwin, Guillaume; Mudd, Simon

2017-04-01

Saltmarshes are highly productive coastal ecosystems that act simultaneously as flood barriers, carbon storage, pollutant filters and nurseries. As halophytic plants trap suspended sediment and decay in the settled strata, innervated platforms emerge from the neighbouring tidal flats, forming sub-vertical scarps on their eroding borders and sub-horizontal pioneer zones in areas of seasonal expansion. These evolutions are subject to two contrasting influences: stochastically generated waves erode scarps and scour tidal flats, whereas tidally-generated currents transport sediment to and from the marsh through the channel network. Hence, the relative power of waves and tidal currents strongly influences saltmarsh evolution, and regional variations in tidal range yield marshes of differing morphologies. We analyse several sheltered saltmarshes to determine how their morphology reflects variations in tidal forcing. Using tidal, topographic and spectral data, we implement an algorithm based on the open-source software LSDTopoTools to automatically identify features such as marsh platforms, tidal flats, erosion scarps, pioneer zones and tidal channels on local Digital Elevation Models. Normalised geometric properties are then computed and compared throughout the spectrum of tidal range, highlighting a notable effect on channel networks, platform geometry and wave exposure. We observe that micro-tidal marshes typically display jagged outlines and multiple islands along with wide, shallow channels. As tidal range increases, we note the progressive disappearance of marsh islands and linearization of scarps, both indicative of higher hydrodynamic stress, along with a structuration of channel networks and the increase of levee volume, suggesting higher sediment input on the platform. Future research will lead to observing and modelling the evolution of saltmarshes under various tidal forcing in order to assess their resilience to environmental change.

Critical role of wind-wave induced erosion on the morphodynamic evolution of shallow tidal basins

NASA Astrophysics Data System (ADS)

D'Alpaos, Andrea; Carniello, Luca; Rinaldo, Andrea

2014-05-01

Wind-wave induced erosion processes are among the chief processes which govern the morphodynamic evolution of shallow tidal basins, both in the vertical and in the horizontal plane. Wind-wave induced bottom shear stresses can promote the disruption of the polymeric microphytobenthic biofilm and lead to the erosion of tidal-flat surfaces and to the increase in suspended sediment concentration which affects the stability of intertidal ecosystems. Moreover, the impact of wind-waves on salt-marsh margins can lead to the lateral erosion of marsh boundaries thus promoting the disappearance of salt-marsh ecosystems. Towards the goal of developing a synthetic theoretical framework to represent wind wave-induced resuspension events and account for their erosional effects on the long-term biomorphodynamic evolution of tidal systems, we have employed a complete, coupled finite element model accounting for the role of wind waves and tidal currents on the hydrodynamic circulation in shallow basins. Our analyses of the characteristics of combined current and wave-induced exceedances in bottom shear stress over a given threshold for erosion, suggest that wind wave-induced resuspension events can be modeled as a marked Poisson process. The interarrival time of wave-induced erosion events is, in fact, an exponentially distributed random variable, as well as the duration and intensity of overthreshold events. Moreover, the analysis of wind-wave induced resuspension events for different historical configurations of the Venice Lagoon from the 19th to the 21st century, shows that the interarrival times of erosion events have dramatically decreased through the last two centuries, whereas the intensities of erosion events have experienced a surprisingly high increase. This allows us to characterize the threatening erosion and degradation processes that the Venice Lagoon has been experiencing since the beginning of the last century.

Nearshore hydrodynamics at pocket beaches with contrasting wave exposure in southern Portugal

NASA Astrophysics Data System (ADS)

Horta, João; Oliveira, Sónia; Moura, Delminda; Ferreira, Óscar

2018-05-01

Pocket beaches on rocky coasts with headlands that control hydro-sedimentary processes are considered to be constrained sedimentary systems, generally with limited sediment inputs. Pocket beaches face severe changes over time. Under worst-case scenarios, these changes can result in the loss of the beach, causing waves to directly attack adjacent cliffs. Studies of nearshore hydrodynamics can help to understand such changes and optimise sediment nourishment procedures. The present work contributes to the knowledge of hydrodynamic forcing mechanisms at pocket beaches by providing a comprehensive description of the nearshore circulation at two beaches with contrasting wave exposures. Two pocket beaches in southern Portugal were studied by combining field measurements of waves and currents with numerical models (STWAVE and BOUSS-2D). The aim of this analysis was to evaluate nearshore hydrodynamics under different wave exposure forcing conditions (e.g. variable wave heights/directions and different tidal levels). The results show that the beach circulation can rapidly shift from longshore-to rip-dominated depending on changes in both the offshore wave direction and tidal levels. Waves with higher obliquity (for both low and moderate wave energy conditions) tend to generate longshore circulation in all considered tidal stages, while waves with lower obliquity tend to produce rip flow with higher-velocity rip currents during low to intermediate tidal stages. The results indicate that the location and intensity of rip currents strongly depend on geomorphological constraints, that is, the control exerted by shore platforms. A larger morphological control is observed at mean sea level because most platforms are submerged/exposed during high/low tide and therefore exert less control on nearshore circulation.

Wave actions and topography determine the small-scale spatial distribution of newly settled Asari clams Ruditapes philippinarum on a tidal flat

NASA Astrophysics Data System (ADS)

Nambu, Ryogen; Saito, Hajime; Tanaka, Yoshio; Higano, Junya; Kuwahara, Hisami

2012-03-01

There are many studies on spatial distributions of Asari clam Ruditapes philippinarum adults on tidal flats but few have dealt with spatial distributions of newly settled Asari clam (<0.3 mm shell length, indicative of settlement patterns) in relation to physical/topographical conditions on tidal flats. We examined small-scale spatial distributions of newly settled individuals on the Matsunase tidal flat, central Japan, during the low spring tides on two days 29th-30th June 2007, together with the shear stress from waves and currents on the flat. The characteristics of spatial distribution of newly settled Asari clam markedly varied depending on both of hydrodynamic and topographical conditions on the tidal flat. Using generalized linear models (GLMs), factors responsible for affecting newly settled Asari clam density and its spatial distribution were distinguished between sampling days, with "crest" sites always having a negative influence each on the density and the distribution on both sampling days. The continuously recorded data for the wave-current flows at the "crest" site on the tidal flat showed that newly settled Asari clam, as well as bottom sediment particles, at the "crest" site to be easily displaced. Small-scale spatial distributions of newly settled Asari clam changed with more advanced benthic stages in relation to the wave shear stress.

Sediment Transport and Infilling of a Borrow Pit on an Energetic Sandy Ebb Tidal Delta Offshore of Hilton Head Island, South Carolina

NASA Astrophysics Data System (ADS)

Wren, A.; Xu, K.; Ma, Y.; Sanger, D.; Van Dolah, R.

2014-12-01

Bottom-mounted instrumentation was deployed at two sites on an ebb tidal delta to measure hydrodynamics, sediment transport, and seabed elevation. One site ('borrow site') was 2 km offshore and used as a dredging site for beach nourishment of nearby Hilton Head Island in South Carolina, and the other site ('reference site') was 10 km offshore and not directly impacted by the dredging. In-situ time-series data were collected during two periods after the dredging: March 15 - June 12, 2012('spring') and August 18 - November 18, 2012 ('fall'). At the reference site directional wave spectra and upper water column current velocities were measured, as well as high-resolution current velocity profiles and suspended sediment concentration profiles in the Bottom Boundary Layer (BBL). Seabed elevation and small-scale seabed changes were also measured. At the borrow site seabed elevation and near-bed wave and current velocities were collected using an Acoustic Doppler Velocimeter. Throughout both deployments bottom wave orbital velocities ranged from 0 - 110 m/s at the reference site. Wave orbital velocities were much lower at the borrow site ranging from 10-20 cm/s, as wave energy was dissipated on the extensive and rough sand banks before reaching the borrow site. Suspended sediment concentrations increased throughout the BBL when orbital velocities increased to approximately 20 cm/s. Sediment grain size and critical shear stresses were similar at both sites, therefore, re-suspension due to waves was less frequent at the borrow site. However, sediment concentrations were highly correlated with the tidal cycle at both sites. Semidiurnal tidal currents were similar at the two sites, typically ranging from 0 - 50 cm/s in the BBL. Maximum currents exceeded the critical shear stress and measured suspended sediment concentrations increased during the first hours of the tidal cycle when the tide switched to flood tide. Results indicate waves contributed more to sediment mobility at the reference site, while tidal forcing was the dominant factor at the borrow site. The seabed elevation data corraborates these results as active migrating ripples of 10 cm were measured at the reference site, while changes in seabed elevation at the borrow site were more gradual with approximately 30 cm of net accretion throughout the study.

Current-induced dissipation in spectral wave models

NASA Astrophysics Data System (ADS)

Rapizo, H.; Babanin, A. V.; Provis, D.; Rogers, W. E.

2017-03-01

Despite many recent developments of the parameterization for wave dissipation in spectral models, it is evident that when waves propagate onto strong adverse currents the rate of energy dissipation is not properly estimated. The issue of current-induced dissipation is studied through a comprehensive data set in the tidal inlet of Port Phillip Heads, Australia. The wave parameters analyzed are significantly modulated by the tidal currents. Wave height in conditions of opposing currents (ebb tide) can reach twice the offshore value, whereas during coflowing currents (flood), it can be reduced to half. The wind-wave model SWAN is able to reproduce the tide-induced modulation of waves and the results show that the variation of currents is the dominant factor in modifying the wave field. In stationary simulations, the model provides an accurate representation of wave height for slack and flood tides. During ebb tides, wave energy is highly overestimated over the opposing current jet. None of the four parameterizations for wave dissipation tested performs satisfactorily. A modification to enhance dissipation as a function of the local currents is proposed. It consists of the addition of a factor that represents current-induced wave steepening and it is scaled by the ratio of spectral energy to the threshold breaking level. The new term asymptotes to the original form as the current in the wave direction tends to zero. The proposed modification considerably improves wave height and mean period in conditions of adverse currents, whereas the good model performance in coflowing currents is unaltered.

Development and the environmental impact analysis of tidal current energy turbines in China

NASA Astrophysics Data System (ADS)

Liu, Yuxin; Ma, Changlei; Jiang, Bo

2018-02-01

Chinese government pays more attentions to renewable energies (RE) in the context of increasing energy demand and climate change problems. As a promising RE, the utilization of marine renewable energy (MRE) is engaging in the world, including the wave energy and tidal current energy mainly. At the same time, the tidal current energy resources in China are abundant. Thus, the utilization of tidal current energy becomes an inevitable choice for China to meet the challenge of global climate change. The Renewable Energy Law (amendment) and “Twelfth Five-Year” Plan of Renewable Energy Development (2011-2015) were released in recent years in China, the tidal current energy are successfully implemented in China, including the R&D and pilot projects. After the summary of the status of tidal current energy converters in recent years in China, especially the devices being in the open sea test. The environmental impact study in China is also introduced in order to offer reference for the environmental impact assessment of tidal current power generation.

Mechanisms of Sediment Transport to an Abandoned Distributary Channel on the Huanghe (Yellow River) Delta, China

NASA Astrophysics Data System (ADS)

Kumpf, L. L.; Kineke, G. C.; Carlson, B.; Mullane, M.

2017-12-01

Avulsions on the fine-grained Huanghe delta have left it scarred with traces of abandoned distributary channels that become intertidal systems, open to water and sediment exchange with the sea. In 1996, an engineered avulsion of the Huanghe left a 30 km long abandoned channel to the south of the modern active river channel. Though all fluvial input was cut off, present-day sedimentation on the new tidal flats has been observed at rates around 2 cm/yr. The source must be suspended-sediment from the Bohai Sea conveyed by the tidal channel network, but the mechanisms promoting sediment import are unknown. Possible mechanisms include (A) import sourced from the sediment-rich buoyant coastal plume, (B) wave resuspension on the shallow shelf, (C) reverse-estuarine residual circulation in the tidal channel, and (D) tidal asymmetry in the channel. Over three summers, in situ measurements of current velocity, suspended-sediment concentration (SSC), and wave climate were made on the delta front, and measurements of velocity, SSC, and salinity were made within the tidal channel. Results suggest that the buoyant plume from the active Huanghe channel can transport sediment south toward the tidal channel mouth (A). Additionally, wave resuspension (B) takes place on the subaqueous topset beds when the significant wave height exceeds 1 m, providing potential sources of suspended-sediment to the tidal channel. Within the abandoned channel, the tidal channel can become hypersaline and exhibit reverse-estuarine circulation (C), which would promote import of turbid coastal water near the surface. Time-series of velocity in the tidal channel indicate that ebb currents are consistently higher than flood currents through the spring-neap cycle (D), with maximum velocities exceeding 1 m/s and corresponding maximum SSC reaching 2 g/L during spring tide. While ebb dominance would typically tend to flush the system of its sediment over time, sediment supplied to the tidal flats may not be removed during the ebb, leading to net accumulation. Flocculation may also enhance settling over the inundated mudflats, contributing to the observed sedimentation. If import and sedimentation proceed at current rates, this abandoned channel may eventually anneal, contributing to the stability of the Huanghe delta.

On generation and evolution of seaward propagating internal solitary waves in the northwestern South China Sea

NASA Astrophysics Data System (ADS)

Xu, Jiexin; Chen, Zhiwu; Xie, Jieshuo; Cai, Shuqun

2016-03-01

In this paper, the generation and evolution of seaward propagating internal solitary waves (ISWs) detected by satellite image in the northwestern South China Sea (SCS) are investigated by a fully nonlinear, non-hydrostatic, three-dimensional Massachusetts Institute of Technology general circulation model (MITgcm). The three-dimensional (3D) modeled ISWs agree favorably with those by satellite image, indicating that the observed seaward propagating ISWs may be generated by the interaction of barotropic tidal flow with the arc-like continental slope south of Hainan Island. Though the tidal current is basically in east-west direction, different types of internal waves are generated by tidal currents flowing over the slopes with different shaped shorelines. Over the slope where the shoreline is straight, only weak internal tides are generated; over the slope where the shoreline is seaward concave, large-amplitude internal bores are generated, and since the concave isobaths of the arc-like continental slope tend to focus the baroclinic tidal energy which is conveyed to the internal bores, the internal bores can efficiently disintegrate into a train of rank-ordered ISWs during their propagation away from the slope; while over the slope where the shoreline is seaward convex, no distinct internal tides are generated. It is also implied that the internal waves over the slope are generated due to mixed lee wave mechanism. Furthermore, the effects of 3D model, continental slope curvature, stratification, rotation and tidal forcing on the generation of ISWs are discussed, respectively. It is shown that, the amplitude and phase speed of ISWs derived from a two-dimensional (2D) model are smaller than those from the 3D one, and the 3D model has an advantage over 2D one in simulating the ISWs generated by the interaction between tidal currents and 3D curved continental slope; the reduced continental slope curvature hinders the extension of ISW crestline; both weaker stratification and rotation suppress the generation of ISWs; and the width of ISW crestline generated by K1 tidal harmonic is longer than that by M2 tidal harmonic.

Tidal Wave Reflectance, Evolution and Distortion in Elkhorn Slough, CA

DTIC Science & Technology

2013-03-01

School O1 Lunisolar diurnal Tidal Constituent ONR Office of Naval Research p Pressure Rhfm High-Frequency Motion Tidal Reflection Coefficient RIVET ...2012 an experiment at the New River Inlet, known as the River and Inlet Dynamics experiment ( RIVET ) was conducted. RIVET 2 is currently scheduled for

Near-Inertial Surface Currents and their influence on Surface Dispersion in the Northeastern Gulf of Mexico near the Deepwater Horizon Oil Spill

NASA Astrophysics Data System (ADS)

Gough, M.; Reniers, A.; MacMahan, J. H.; Howden, S. D.

2014-12-01

The continental shelf along the northeastern Gulf of Mexico is transected by the critical latitude (30°N) for inertial motions. At this latitude the inertial period is 24 hours and diurnal surface current oscillations can amplify due to resonance with diurnal wind and tidal forcing. Tidal amplitudes are relatively small in this region although K1 tidal currents can be strong over the shelf west of the DeSoto Canyon where the K1 tide propagates onshore as a Sverdrup wave. Other sources of diurnal motions include internal tidal currents, Poincaré waves, and basin resonance. It is therefore very difficult to separate inertial wind-driven motions from other diurnal motions. Spatiotemporal surface currents were measured using hourly 6 km resolution HF radar data collected in June 2010 during the Deepwater Horizon oil spill and July 2012 during the Grand Lagrangian Deployment (GLAD). Surface currents were also measured using GLAD GPS-tracked drifters. NDBC buoy wind data were used to determine wind-forcing, and OSU Tidal Inversion Software (OTIS) were used to predict tidal currents. The relative spatiotemporal influence of diurnal wind and tidal forcing on diurnal surface current oscillations is determined through a series of comparative analyses: phase and amplitude of bandpassed timeseries, wavelet analyses, wind-driven inertial oscillation calculations, and tidal current predictions. The wind-driven inertial ocean response is calculated by applying a simple "slab" model where wind-forcing is allowed to excite a layer of low-density water riding over high density water. The spatial variance of diurnal motions are found to be correlated with satellite turbidity imagery indicating that stratification influences the sea surface inertial response to wind-forcing. Surface dispersion is found to be minimized in regions of high diurnal variance suggesting that mean surface transport is restricted in regions of inertial motions associated with stratification.

Tidal inlet response to sediment infilling of the associated bay and possible implications of human activities: the Marennes-Oléron Bay and the Maumusson Inlet, France

NASA Astrophysics Data System (ADS)

Bertin, Xavier; Chaumillon, Eric; Sottolichio, Aldo; Pedreros, Rodrigo

2005-06-01

Tidal inlet characteristics are controlled by wave energy, tidal range, tidal prism, sediment supply and direction and rates of sand delivered to the inlet. This paper deals with the relations between inlet and lagoon evolutions, linked by the tidal prism. Our study is focused on the Maumusson Inlet and the Marennes-Oléron Bay (first oyster farming area in Europe), located on the western coast of France. The tidal range (2-6 m) and wave climate (mean height: 1.5 m) place this tidal inlet system in the mixed energy (tide, waves), tide-dominated category. The availability of high-resolution bathymetric data since 1824 permits to characterise and quantify accurately morphological changes of both the inlet and the tidal bay. Since 1824, sediment filling of the tidal bay has led to a 20% decrease in its water volume, and a 35% reduction of the inlet throat section. Furthermore, the bay is subjected to a very high anthropic pressure, mainly related to oyster farming. Thus, both natural and human-related processes seem relevant to explain high sedimentation rates. Current measurements, hydrodynamic modelling and cross-sectional area of the inlet throat are used in order to quantify tidal prism changes since 1824. Both flood and ebb tidal prism decreased by 35%. Decrease in the Marennes-Oléron Bay water volume is inferred to be responsible for a part of tidal prism decrease at the inlet. Tidal prisms decrease may also be explained by an increase in frictional resistance to tidal wave propagation, due to a general shoaling and oyster farms in the bay. A conceptual model is proposed, taking into account natural and human-related sedimentation processes, and explaining tidal inlet response to tidal bay evolutions.

Reprint of Mechanisms of maintaining high suspended sediment concentration over tide-dominated offshore shoals in the southern Yellow Sea

NASA Astrophysics Data System (ADS)

Xiong, Jilian; Wang, Xiao Hua; Wang, Ya Ping; Chen, Jingdong; Shi, Benwei; Gao, Jianhua; Yang, Yang; Yu, Qian; Li, Mingliang; Yang, Lei; Gong, Xulong

2018-06-01

An understanding of the dynamics and behaviors of suspended sediments is vital in analysis of morphological, environmental, and ecological processes occurring in coastal marine environments. To study the mechanisms of maintaining high suspended sediment concentrations (SSCs) on a tide-dominated offshore shoal, we measured water depths, current velocities, SSCs, wave parameters and bottom sediment compositions in the southern Yellow Sea. These data were then used to calculate bottom shear stresses generated by currents (τc), waves (τw), and wave-current interactions (τcw). SSCs time series exhibited strong quarter-diurnal peaks during spring tides, in contrast to the semidiurnal signal during neap tides. A Fourier analysis showed that suspended sediment variations within tidal cycles was mainly controlled by resuspension in most stations. There existed relatively stable background SSCs (maintaining high SSCs among tidal cycles) values at all four stations during both windy (wind speed > 9.0 m/s) and normal weather conditions (wind speed < 3.0 m/s). The background SSCs had strong relationship with spring/neap-averaged τcw, indicating background SSCs were mainly controlled by mean bottom shear stress, with a minimum value of 0.21 N/m2. On account of the strong tidal currents, background SSCs of spring tides were greater than that of neap tides. In addition, on the base of wavelet, statistics analyses and turbulence dissipation parameter, background SSCs during slack tide in the study area may be maintained by intermittent turbulence events induced by a combined tidal current and wave action.

Mechanisms of maintaining high suspended sediment concentration over tide-dominated offshore shoals in the southern Yellow Sea

NASA Astrophysics Data System (ADS)

Xiong, Jilian; Wang, Xiao Hua; Wang, Ya Ping; Chen, Jingdong; Shi, Benwei; Gao, Jianhua; Yang, Yang; Yu, Qian; Li, Mingliang; Yang, Lei; Gong, Xulong

2017-05-01

An understanding of the dynamics and behaviors of suspended sediments is vital in analysis of morphological, environmental, and ecological processes occurring in coastal marine environments. To study the mechanisms of maintaining high suspended sediment concentrations (SSCs) on a tide-dominated offshore shoal, we measured water depths, current velocities, SSCs, wave parameters and bottom sediment compositions in the southern Yellow Sea. These data were then used to calculate bottom shear stresses generated by currents (τc), waves (τw), and wave-current interactions (τcw). SSCs time series exhibited strong quarter-diurnal peaks during spring tides, in contrast to the semidiurnal signal during neap tides. A Fourier analysis showed that suspended sediment variations within tidal cycles was mainly controlled by resuspension in most stations. There existed relatively stable background SSCs (maintaining high SSCs among tidal cycles) values at all four stations during both windy (wind speed > 9.0 m/s) and normal weather conditions (wind speed < 3.0 m/s). The background SSCs had strong relationship with spring/neap-averaged τcw, indicating background SSCs were mainly controlled by mean bottom shear stress, with a minimum value of 0.21 N/m2. On account of the strong tidal currents, background SSCs of spring tides were greater than that of neap tides. In addition, on the base of wavelet, statistics analyses and turbulence dissipation parameter, background SSCs during slack tide in the study area may be maintained by intermittent turbulence events induced by a combined tidal current and wave action.

Preliminary assessment of landslide-induced wave hazards, Tidal Inlet, Glacier Bay National Park, Alaska

USGS Publications Warehouse

Wieczorek, Gerald F.; Jakob, Matthias; Motyka, Roman J.; Zirnheld, Sandra L.; Craw, Patricia

2003-01-01

A large potential rock avalanche above the northern shore of Tidal Inlet, Glacier Bay National Park, Alaska, was investigated to determine hazards and risks of landslide-induced waves to cruise ships and other park visitors. Field and photographic examination revealed that the 5 to 10 million cubic meter landslide moved between AD 1892 and 1919 after the retreat of Little Ice Age glaciers from Tidal Inlet by AD 1890. The timing of landslide movement and the glacial history suggest that glacial debuttressing caused weakening of the slope and that the landslide could have been triggered by large earthquakes of 1899-1900 in Yakutat Bay. Evidence of recent movement includes fresh scarps, back-rotated blocks, and smaller secondary landslide movements. However, until there is evidence of current movement, the mass is classified as a dormant rock slump. An earthquake on the nearby active Fairweather fault system could reactivate the landslide and trigger a massive rock slump and debris avalanche into Tidal Inlet. Preliminary analyses show that waves induced by such a landslide could travel at speeds of 45 to 50 m/s and reach heights up to 76 m with wave runups of 200 m on the opposite shore of Tidal Inlet. Such waves would not only threaten vessels in Tidal Inlet, but would also travel into the western arm of Glacier Bay endangering large cruise ships and their passengers.

Measuring the neutron star tidal deformability with equation-of-state-independent relations and gravitational waves

NASA Astrophysics Data System (ADS)

Chatziioannou, Katerina; Haster, Carl-Johan; Zimmerman, Aaron

2018-05-01

Gravitational wave measurements of binary neutron star coalescences offer information about the properties of the extreme matter that comprises the stars. Despite our expectation that all neutron stars in the Universe obey the same equation of state, i.e. the properties of the matter that forms them are universal, current tidal inference analyses treat the two bodies as independent. We present a method to measure the effect of tidal interactions in the gravitational wave signal—and hence constrain the equation of state—that assumes that the two binary components obey the same equation of state. Our method makes use of a relation between the tidal deformabilities of the two stars given the ratio of their masses, a relation that has been shown to only have a weak dependence on the equation of state. We use this to link the tidal deformabilities of the two stars in a realistic parameter inference study while simultaneously marginalizing over the error in the relation. This approach incorporates more physical information into our analysis, thus leading to a better measurement of tidal effects in gravitational wave signals. Through simulated signals we estimate that uncertainties in the measured tidal parameters are reduced by a factor of at least 2—and in some cases up to 10—depending on the equation of state and mass ratio of the system.

The effect of wind waves on spring-neap variations in sediment transport in two meso-tidal estuarine basins with contrasting fetch

NASA Astrophysics Data System (ADS)

Hunt, Stephen; Bryan, Karin R.; Mullarney, Julia C.

2017-03-01

Higher-energy episodic wind-waves can substantially modify estuarine morphology over short timescales which are superimposed on lower-energy but long-term tidal asymmetry effects. Theoretically, wind waves and tidal currents change the morphology through their combined influence on the asymmetry between bed shear stress, τmax, on the flood and ebb tide, although the relative contribution of such wind-wave events in shaping the long-term morphological evolution in real estuaries is not well known. If the rising tide reaches sufficiently high water depths, τmax decreases as water depth increases because of the depth attenuation of wave orbital velocities. However, this effect is opposed by the increase in τmax associated with the longer fetch occurring at high tide, which allows the generation of larger waves. Additionally, these effects are superimposed on the spring-neap variations in current associated with changes to tidal range. By comparing two mesotidal basins in the same dendritic estuary, one with a large fetch aligned with the prevailing wind direction and one with only a small fetch, we show that for a sufficiently large fetch even the small and frequently occurring wind events are able to create waves that are capable of changing the morphology ('morphologically significant'). Conversely, in the basin with reduced fetch, these waves are generated less frequently and therefore are of reduced morphological significance. Here, we find that although tidal current should be stronger during spring tides and alter morphology more, on average the reduced fetch and increased water depth during spring tides mean that the basin-averaged intertidal τmax is similar during both spring and neap tides. Moreover, in the presence of wind waves, the duration of slack water is reduced during neap tides relative to spring tides, resulting in a reduced chance for accretion during neap tides. Finally, τmax is lower in the subtidal channels during neaps than springs but of a similar magnitude over the intertidal areas, and so sediment is more likely to be advected from the intertidal regions during neap tides rather than springs. This spring-neap cycle in sediment transport potential is in sharp contrast to that found previously in microtidal wave-dominated environments, where spring tides are expected to enhance erosion.

Spatial variability of sediment transport processes over intra‐ and subtidal timescales within a fringing coral reef system

USGS Publications Warehouse

Pomeroy, Andrew; Lowe, Ryan J.; Ghisalberti, Marco; Winter, Gundula; Storlazzi, Curt D.; Cuttler, Michael V. W.

2018-01-01

Sediment produced on fringing coral reefs that is transported along the bed or in suspension affects ecological reef communities as well as the morphological development of the reef, lagoon, and adjacent shoreline. This study quantified the physical process contribution and relative importance of incident waves, infragravity waves, and mean currents to the spatial and temporal variability of sediment in suspension. Estimates of bed shear stresses demonstrate that incident waves are the key driver of the SSC variability spatially (reef flat, lagoon, and channels) but cannot not fully describe the SSC variability alone. The comparatively small but statistically significant contribution to the bed shear stress by infragravity waves and currents, along with the spatial availability of sediment of a suitable size and volume, is also important. Although intra‐tidal variability in SSC occurs in the different reef zones, the majority of the variability occurs over longer slowly varying (subtidal) time scales, which is related to the arrival of large incident waves at a reef location. The predominant flow pathway, which can transport suspended sediment, consists of cross‐reef flow across the reef flat that diverges in the lagoon and returns offshore through channels. This pathway is primarily due to subtidal variations in wave‐driven flows, but can also be driven alongshore by wind stresses when the incident waves are small. Higher frequency (intra‐tidal) current variability also occur due to both tidal flows, as well as variations in the water depth that influence wave transmission across the reef and wave‐driven currents.

Airborne synthetic aperture radar tracking of internal waves in the Strait of Gibraltar

NASA Astrophysics Data System (ADS)

Richez, Claude

As part of the International “Gibraltar Experiment”, we realized, on June 22 and 24, 1986, two surveys of the Strait of Gibraltar, on board an aircraft equipped with a Synthetic Aperture Radar. Our objective was to observe, at Spring tides, and during two twelve-hour tidal cycles, at 24 h interval, the generation of internal wave trains, linked to the hydraulic jump formed west of the sill during the westward phase of the tidal current, and their eastward propagation in the Strait. The speed of propagation of these waves and the effect of the diurnal component of the tide on their generation and propagation could then be determined. Our results suggest that two solitary waves of equal amplitude propagated eastwards in the strait on June 22 (the tidal coefficient being equal to 92), with a speed, relative to the ground, of 2.1 to 2.6 m s -1. 24 h later, during the second survey, on June 24 (tidal coefficient 90), we observed the propagation of a train of non-linear waves, the speed of the leading wave of which being about 1.9 ms -1. Our data show that other waves pass over the Camarinal Sill after the release of the bore, and “secondary” internal wave trains are shown to propagate eastwards from there. Although our SAR data show the appearance of waves west of the northern sill at about 4 h after High Water (HW), the mechanism leading to their generation is not clear. These waves could propagate eastwards, all along the strait, and/or northwestwards along the western Spanish coast. They could be responsible for the solitary-type events observed at the eastern entrance of the strait, at about 7 h after HW, by ZIEGENBEIN (1969, 1970). These events are noticeable in the hydrological parameters time series of ARMI and FARMER (1988) and in the high rate current data (2-min apart) from their April 1986 cruise. Besides these alongstrait waves, our SAR data show the existence of cross-strait waves, and give an idea of their wavelength and speed of propagation. Their presence leads to perturbations in the current, revealed by simultaneous current data, at the Camarinal Sill and north of Cape Cires.

Wave-current interaction in Willapa Bay

USGS Publications Warehouse

Olabarrieta, Maitane; Warner, John C.; Kumar, Nirnimesh

2011-01-01

This paper describes the importance of wave-current interaction in an inlet-estuary system. The three-dimensional, fully coupled, Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system was applied in Willapa Bay (Washington State) from 22 to 29 October 1998 that included a large storm event. To represent the interaction between waves and currents, the vortex-force method was used. Model results were compared with water elevations, currents, and wave measurements obtained by the U.S. Army Corp of Engineers. In general, a good agreement between field data and computed results was achieved, although some discrepancies were also observed in regard to wave peak directions in the most upstream station. Several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind, tide, and wave-current interaction process. Comparison of the horizontal momentum balances results identified that wave-breaking-induced acceleration is one of the leading terms in the inlet area. The enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress. The pressure gradient showed significant changes with respect to the pure tidal case. During storm conditions the momentum balance in the inlet shares the characteristics of tidal-dominated and wave-dominated surf zone environments. The changes in the momentum balance caused by waves were manifested both in water level and current variations. The most relevant effect on hydrodynamics was a wave-induced setup in the inner part of the estuary.

Wave-current interactions at the FloWave Ocean Energy Research Facility

NASA Astrophysics Data System (ADS)

Noble, Donald; Davey, Thomas; Steynor, Jeffrey; Bruce, Tom; Smith, Helen; Kaklis, Panagiotis

2015-04-01

Physical scale model testing is an important part of the marine renewable energy development process, allowing the study of forces and device behaviour in a controlled environment prior to deployment at sea. FloWave is a new state-of-the-art ocean energy research facility, designed to provide large scale physical modelling services to the tidal and wave sector. It has the unique ability to provide complex multi-directional waves that can be combined with currents from any direction in the 25m diameter circular tank. The facility is optimised for waves around 2s period and 0.4m height, and is capable of generating currents upwards of 1.6m/s. This offers the ability to model metocean conditions suitable for most renewable energy devices at a typical scale of between 1:10 and 1:40. The test section is 2m deep, which can be classed as intermediate-depth for most waves of interest, thus the full dispersion equation must be solved as the asymptotic simplifications do not apply. The interaction between waves and currents has been studied in the tank. This has involved producing in the tank sets of regular waves, focussed wave groups, and random sea spectra including multi-directional sea states. These waves have been both inline-with and opposing the current, as well as investigating waves at arbitrary angles to the current. Changes in wave height and wavelength have been measured, and compared with theoretical results. Using theoretical wave-current interaction models, methods have been explored to "correct" the wave height in the central test area of the tank when combined with a steady current. This allows the wave height with current to be set equal to that without a current. Thus permitting, for example, direct comparison of device motion response between tests with and without current. Alternatively, this would also permit a specific wave height and current combination to be produced in the tank, reproducing recorded conditions at a particular site of interest. The initial tests used a correction factor based on a linear combination of wave and current (Smith 1997), which was found to be reasonably accurate, although the requirement for higher order theory is also explored. FloWave is a new facility that offers the ability to study wave-current interactions at arbitrary angles with relatively fast currents. This is important as waves and tidal currents at sites of interest for renewable energy generation may not be aligned (Lewis et al. 2014), and so better understanding of these conditions is required. References Lewis, M.J. et al., 2014. Realistic wave conditions and their influence on quantifying the tidal stream energy resource. Applied Energy, 136, pp.495-508. Smith, J.M., 1997. Coastal Engineering Technical Note One-dimensional wave-current interaction (CETN IV-9), Vicksburg, MS.

The dependence of estuarine turbidity on tidal intrusion length, tidal range and residence time

USGS Publications Warehouse

Uncles, R.J.; Stephens, J.A.; Smith, R.E.

2002-01-01

It is shown that there is a marked tendency for long, strongly tidal estuaries to have greater suspended particulate matter (SPM) concentrations within their high-turbidity regions than shorter estuaries with comparable tidal ranges at their mouths, or weakly tidal estuaries. Using consistently derived data from 44 estuaries in Europe and the Americas, contours of the logarithm of maximum estuarine SPM concentration are shown to be reasonably smooth when plotted against the logarithm of mean spring tidal range (at the estuary mouth) and the logarithm of estuarine tidal length. Predictions from the plot are compared with published observations made in the Delaware, Scheldt, Rio de la Plata, Gironde, Bay of Fundy, Changjiang (Yangtze), Amazon, Paros Lagoon and the Hawkesbury Estuary and it is shown that, qualitatively, there are no serious discrepancies. Short, weakly tidal estuaries are predicted to have very low 'intrinsic' SPM concentrations. High SPM concentrations in these estuaries would most likely be the result of either locally generated wave resuspension, high freshwater sediment loads due to freshets, or intruding seawater carrying suspended sediments derived from wave activity in the coastal zone. Application of a generic tidal model demonstrates that longer estuaries possess faster tidal currents for a given tidal range at their mouth and, in the presence of a supply of erodable fine sediment, therefore (by implication) produce greater concentrations of SPM that can be accumulated within a turbidity maximum. The same is true if the tidal range is increased for estuaries of a given length. These features are illustrated by comparing surveys of SPM data from two large estuaries possessing greatly different tidal ranges (the microtidal, medium turbidity Potomac and the macrotidal, highly turbid Humber-Ouse) and a third, much smaller but strongly tidal estuary (the low-turbidity Tweed). It is demonstrated that longer estuaries tend to have longer flushing times for solutes than shorter systems and that larger tides tend to reduce flushing times, although the tidal influence is secondary. Short, rapidly flushed estuaries quickly lose their erodable fine sediment to the coastal zone during freshets and during the ebbing currents of spring tides. Turbidity is therefore small during low runoff, low wave activity conditions. Very long, very slowly flushed estuaries are unlikely to lose a significant fraction of their resuspended sediments during freshets or individual ebb tides and are therefore able to accumulate large and increasing amounts of fine sediment in the long-term. Turbidity within them is therefore high during the fast currents of large spring tides. ?? 2002 Elsevier Science Ltd. All rights reserved.

The dependence of estuarine turbidity on tidal intrusion length, tidal range and residence time

USGS Publications Warehouse

Uncles, R.J.; Stephens, J.A.; Smith, R.E.

2002-01-01

It is shown that there is a marked tendency for long, strongly tidal estuaries to have greater suspended particulate matter (SPM) concentrations within their high-turbidity regions than shorter estuaries with comparable tidal ranges at their mouths, or weakly tidal estuaries. Using consistently derived data from 44 estuaries in Europe and the Americas, contours of the logarithm of maximum estuarine SPM concentration are shown to be reasonably smooth when plotted against the logarithm of mean spring tidal range (at the estuary mouth) and the logarithm of estuarine tidal length. Predictions from the plot are compared with published observations made in the Delaware, Scheldt, Rio de la Plata, Gironde, Bay of Fundy, Changjiang (Yangtze), Amazon, Patos Lagoon and the Hawkesbury Estuary and it is shown that, qualitatively, there are no serious discrepancies. Short, weakly tidal estuaries are predicted to have very low ‘intrinsic’ SPM concentrations. High SPM concentrations in these estuaries would most likely be the result of either locally generated wave resuspension, high freshwater sediment loads due to freshets, or intruding seawater carrying suspended sediments derived from wave activity in the coastal zone. Application of a generic tidal model demonstrates that longer estuaries possess faster tidal currents for a given tidal range at their mouth and, in the presence of a supply of erodable fine sediment, therefore (by implication) produce greater concentrations of SPM that can be accumulated within a turbidity maximum. The same is true if the tidal range is increased for estuaries of a given length. These features are illustrated by comparing surveys of SPM data from two large estuaries possessing greatly different tidal ranges (the microtidal, medium turbidity Potomac and the macrotidal, highly turbid Humber-Ouse) and a third, much smaller but strongly tidal estuary (the low-turbidity Tweed). It is demonstrated that longer estuaries tend to have longer flushing times for solutes than shorter systems and that larger tides tend to reduce flushing times, although the tidal influence is secondary. Short, rapidly flushed estuaries quickly lose their erodable fine sediment to the coastal zone during freshets and during the ebbing currents of spring tides. Turbidity is therefore small during low runoff, low wave activity conditions. Very long, very slowly flushed estuaries are unlikely to lose a significant fraction of their resuspended sediments during freshets or individual ebb tides and are therefore able to accumulate large and increasing amounts of fine sediment in the long-term. Turbidity within them is therefore high during the fast currents of large spring tides.

75 FR 5708 - Ocean Dumping; Designation of Ocean Dredged Material Disposal Sites Offshore of the Siuslaw River...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-04

... suspended by wave action near the bottom, and are moved by bottom currents or directly as bedload. Tidal, wind and wave forces contribute to generating bottom currents, which act in relation to the sediment... littoral zone, limit wave effects due to mounding, and keep material from reentering the navigation channel...

A Permo-Carboniferous tide-storm interactive system: Talchir formation, Raniganj Basin, India

NASA Astrophysics Data System (ADS)

Bhattacharya, H. N.; Bhattacharya, Biplab

2006-08-01

Sandstone/siltstone-mudstone interbedded facies of the Permo-Carboniferous Talchir formation, Gondwana Supergroup, is exposed in the Raniganj Basin and records the activities of tidal currents in a terminoglacial, storm-influenced shallow marine setting. Tidal bundles of various types with pause plane drapes, evidence of time-velocity asymmetry and rare bidirectional current flow patterns are indicative of tidal activity. Chance preservation of such structures from storm reworking might have occurred due to dampening of storm waves on the low-gradient muddy substrate of the tidal flat. The tide-generated stratifications are draped by over-thickened muddy-siltstone with wavy/hummocky laminations. Increased suspended sediment concentrations following a storm yielded such thick mudstone drapes. Thin beds containing tidal structures indicate poor sediment supply in a blind tidal embayment.

On the dynamics of the Mouth of the Columbia River: Results from a three-dimensional fully coupled wave-current interaction model

NASA Astrophysics Data System (ADS)

Akan, Çiǧdem; Moghimi, Saeed; Özkan-Haller, H. Tuba; Osborne, John; Kurapov, Alexander

2017-07-01

Numerical simulations were performed using a 3-D ocean circulation model (ROMS) two-way coupled to a phase-averaged wave propagation model (SWAN), to expand our understanding of the dynamics of wave-current interactions at the Mouth of the Columbia River (MCR). First, model results are compared with water elevations, currents, temperature, salinity, and wave measurements obtained by the U.S. Army Corp of Engineers during the Mega-Transect Experiment in 2005. We then discuss the effects of the currents on the waves and vice versa. Results show that wave heights are intensified notably at the entrance of the mouth in the presence of the tidal currents, especially in ebb flows. We also find nonlocal modifications to the wave field because of wave focusing processes that redirect wave energy toward the inlet mouth from adjacent areas, resulting in the presence of a tidal signatures in areas where local currents are weak. The model also suggests significant wave amplification at the edge of the expanding plume in the later stages of ebb, some tens of kilometers offshore of the inlet mouth, with potential implications for navigation safety. The effect of waves on the location of the plume is also analyzed, and results suggest that the plume is shifted in the down-wave direction when wave effects are considered, and that this shift is more pronounced for larger waves, and consistent with the presence of alongshore advection terms in the salt advection equation, which are related to the Stokes velocities associated with waves.

A life-cycle model for wave-dominated tidal inlets along passive margin coasts of North America

NASA Astrophysics Data System (ADS)

Seminack, Christopher T.; McBride, Randolph A.

2018-03-01

A regional overview of 107 wave-dominated tidal inlets along the U.S. Atlantic coast, U.S. Gulf of Mexico coast, and Canadian Gulf of St. Lawrence coast yielded a generalized wave-dominated tidal inlet life-cycle model that recognized the rotational nature of tidal inlets. Tidal inlets are influenced by concurrently acting processes transpiring over two timescales: short-term, event-driven processes and long-term, evolutionary processes. Wave-dominated tidal inlets are classified into three rotational categories based on net longshore sediment transport direction and rotation direction along the landward (back-barrier) portion of the inlet channel: downdrift channel rotation, updrift channel rotation, or little-to-no channel rotation. Lateral shifting of the flood-tidal delta depocenter in response to available estuarine accommodation space appears to control inlet channel rotation. Flood-tidal delta deposits fill accommodation space locally within the estuary (i.e., creating bathymetric highs), causing the tidal-inlet channel to rotate. External influences, such as fluvial discharge, pre-existing back-barrier channels, and impeding salt marsh will also influence inlet-channel rotation. Storm events may rejuvenate the tidal inlet by scouring sediment within the flood-tidal delta, increasing local accommodation space. Wave-dominated tidal inlets are generally unstable and tend to open, concurrently migrate laterally and rotate, infill, and close. Channel rotation is a primary reason for wave-dominated tidal inlet closure. During rotation, the inlet channel lengthens and hydraulic efficiency decreases, thus causing tidal prism to decrease. Tidal prism, estuarine accommodation space, and sediment supply to the flood-tidal delta are the primary variables responsible for tidal inlet rotation. Stability of wave-dominated tidal inlets is further explained by: stability (S) = tidal prism (Ω) + estuarine accommodation space (V) - volume of annual sediment supply (Mt). Rotating wave-dominated tidal inlets follow a six-stage evolutionary model; whereas wave-dominated tidal inlets that exhibit little-to-no rotation follow a five-stage evolutionary model.

Offshore Energy Mapping for Northeast Atlantic and Mediterranean: MARINA PLATFORM project

NASA Astrophysics Data System (ADS)

Kallos, G.; Galanis, G.; Spyrou, C.; Kalogeri, C.; Adam, A.; Athanasiadis, P.

2012-04-01

Deep offshore ocean energy mapping requires detailed modeling of the wind, wave, tidal and ocean circulation estimations. It requires also detailed mapping of the associated extremes. An important issue in such work is the co-generation of energy (generation of wind, wave, tides, currents) in order to design platforms on an efficient way. For example wind and wave fields exhibit significant phase differences and therefore the produced energy from both sources together requires special analysis. The other two sources namely tides and currents have different temporal scales from the previous two. Another important issue is related to the estimation of the environmental frequencies in order to avoid structural problems. These are issues studied at the framework of the FP7 project MARINA PLATFORM. The main objective of the project is to develop deep water structures that can exploit the energy from wind, wave, tidal and ocean current energy sources. In particular, a primary goal will be the establishment of a set of equitable and transparent criteria for the evaluation of multi-purpose platforms for marine renewable energy. Using these criteria, a novel system set of design and optimisation tools will be produced addressing new platform design, component engineering, risk assessment, spatial planning, platform-related grid connection concepts, all focussed on system integration and reducing costs. The University of Athens group is in charge for estimation and mapping of wind, wave, tidal and ocean current resources, estimate available energy potential, map extreme event characteristics and provide any additional environmental parameter required.

Intermittent large amplitude internal waves observed in Port Susan, Puget Sound

NASA Astrophysics Data System (ADS)

Harris, J. C.; Decker, L.

2017-07-01

A previously unreported internal tidal bore, which evolves into solitary internal wave packets, was observed in Port Susan, Puget Sound, and the timing, speed, and amplitude of the waves were measured by CTD and visual observation. Acoustic Doppler current profiler (ADCP) measurements were attempted, but unsuccessful. The waves appear to be generated with the ebb flow along the tidal flats of the Stillaguamish River, and the speed and width of the resulting waves can be predicted from second-order KdV theory. Their eventual dissipation may contribute significantly to surface mixing locally, particularly in comparison with the local dissipation due to the tides. Visually the waves appear in fair weather as a strong foam front, which is less visible the farther they propagate.

Characterising the spatial variability of the tidal stream energy resource from floating turbines

NASA Astrophysics Data System (ADS)

Ward, Sophie; Neill, Simon; Robins, Peter

2017-04-01

The shelf seas, in particular the northwest European shelf seas surrounding the UK, contain significant tidal power potential. Tidal stream energy is both predictable and reliable providing that sites are well-selected based upon the hydrodynamic regime and the device specifics. In this high resolution three-dimensional tidal modelling study, we investigate how the tidal stream resource around the Welsh coast (UK) varies with water depth and location, with particular focus on the Pembrokeshire region. The potential extractable energy for a floating tidal stream energy converter is compared with that for a bottom-fixed device, highlighting the need to vary the resource characterisation criteria based on device specifics. We demonstrate how small variations in the tidal current speeds - with hub depth or due to tidal asymmetry - can lead to substantial variations in potential power output. Further, the results indicate that power generation from floating tidal energy converters will be more significantly influenced by tidal elevations in regions characterised by a lower tidal range (more progressive waves) than regions that experience a high tidal range (standing waves). As numerical modelling capacity improves and tidal stream energy converter technologies develop, ongoing improved quantification of the tidal resource is needed, as well as consideration of the possible feedbacks of the devices and energy extraction on the hydrodynamic regime and the surrounding area.

Low energy, low latitude wave-dominated shallow marine depositional systems: examples from northern Borneo

NASA Astrophysics Data System (ADS)

Lambiase, Joseph J.; Suraya Tulot

2013-12-01

The depositional environments of the wave-dominant successions in the middle to late Miocene Belait and Sandakan Formations in northwestern and northern Borneo, respectively, were determined based on grain size distributions, sedimentary structures and facies successions, as well as trace and microfossil assemblages. Generally, progradational shoreface successions in the Belait Formation were deposited in very low wave energy environments where longshore currents were too weak to generate trough cross-bedding. Shoreface sands are laterally continuous for several km and follow the basin contours, suggesting attached beaches similar to the modern Brunei coastline. In contrast, trough cross-bedding is common in the coarser Sandakan Formation and back-barrier mangrove swamp deposits cap the progradational succession as on the modern northern Dent Peninsula coastline, indicating barrier development and higher wave energy conditions than in the Belait Formation. The Borneo examples indicate that barrier systems that include significant tidal facies form under higher wave energy conditions than attached beaches with virtually no tidal facies. Also, Borneo's low latitude climate promotes back-barrier mangrove which reduces tidal exchange and reduces tidal influence relative to comparable temperate climate systems. The results of the study indicate that depositional systems on low energy, wave-dominated coasts are highly variable, as are the sand bodies and facies associations they generate.

Semi-isolated, flat-topped carbonate platform (Oligo-Miocene, Sardinia, Italy): Sedimentary architecture and processes

NASA Astrophysics Data System (ADS)

Andreucci, Stefano; Pistis, Marco; Funedda, Antonio; Loi, Alfredo

2017-11-01

The Chattian-Aquitanian carbonate system of Isili sub-basin (SE Sardinia, Italy) were studied to better understand the hydrodynamic processes controlling the formation of landward-downlapping, rhodolith-rich, giant clinoforms. The studied flat-topped platform was attached to an island (semi-isolated) and migrated onshore (landward) over a shallow marine, protected embayment. The depositional profile is characterized by four, sea to land, zones: seaward slope, flat-topped platform (submerged flat), landward slope and mixed siliciclastic-carbonate embayment. In particular, these zones record different levels, from high to moderate, of hydrodynamic energy and persistency. The paleodepth of the studied succession, based on T/D test on Amphistegina specimens, red-algal genera and geometric reconstruction of the overall system, ranges from - 10 to - 30 m for the platform up to around - 40 m for the landward slope base. Thus, the flat-topped platform was permanently submerged and an extensive carbonate (sea grass, algal and bryozoan-algal) factory along with oyster framestones developed. The widespread presence in the barren zones of rhodolith-to-shell rich small to very small compound dunes (high-energy zone) suggests that the flat-topped platform was periodically swept by unidirectional, landward-directed currents. These currents allow the formation of large-scale, rhodolith-rich clinobeds along the landward slope (washover fan-like system). The presence of rodolith pavements developed along the flat-topped platform at or slightly below the fairweather wave base suggests that clinobeds were formed in a nearshore, shallow subtidal setting. Finally, the shallow marine, protected embayment (moderate-energy zone) represents the widening distal reaches of the currents flowing or along the clinoforms or from the coast basinward (river floods and/or ebb tidal currents). Despite few tidal-related sedimentary structures such as bi-directional ripples and small compound dunes separated by finer-grained ;drapes; or reactivation surfaces were observed, the prevailing processes acting over the platform are unidirectional, landward-directed currents possibly associated with longshore currents and/or wave actions. However, the resultant migration of the whole system onshore (landward) cannot be easily explained with storm or wind-related processes. Thus the studied flat-topped platform seems to be controlled by long term tidal regulation within a meso to macro tidal regime. In particular, such meso/macro tidal environments experience multiannual to multidecennial phases of stronger/weaker tidal range fluctuations resembling periods of relatively sea highs and lows with respect to the mean sea level (0 m). All the (wind, storm, wave and tidal) currents sweeping the flat-topped platform were maxima during phases of strong tidal fluctuations generating erosion and sediment transportation over the flat and accumulation on the landward slope (clinobeds). Conversely, during phases of weaker tidal range fluctuations overall currents were minima, clinoforms did not develop and factories widespread re-colonized the submerged flat. Therefore, the studied platform developed in a current-dominated and tidal modulated setting. Finally, the studied carbonates of Sardinia suggest that the Sardinian seaway and the incipient Provençal basin during the Chattian-Aquitanian were, locally, capable to generate meso to macro tidal conditions.

Between tide and wave marks: a unifying model of physical zonation on littoral shores

PubMed Central

Bird, Christopher E.; Franklin, Erik C.; Smith, Celia M.

2013-01-01

The effects of tides on littoral marine habitats are so ubiquitous that shorelines are commonly described as ‘intertidal’, whereas waves are considered a secondary factor that simply modifies the intertidal habitat. However mean significant wave height exceeds tidal range at many locations worldwide. Here we construct a simple sinusoidal model of coastal water level based on both tidal range and wave height. From the patterns of emergence and submergence predicted by the model, we derive four vertical shoreline benchmarks which bracket up to three novel, spatially distinct, and physically defined zones. The (1) emergent tidal zone is characterized by tidally driven emergence in air; the (2) wave zone is characterized by constant (not periodic) wave wash; and the (3) submergent tidal zone is characterized by tidally driven submergence. The decoupling of tidally driven emergence and submergence made possible by wave action is a critical prediction of the model. On wave-dominated shores (wave height ≫ tidal range), all three zones are predicted to exist separately, but on tide-dominated shores (tidal range ≫ wave height) the wave zone is absent and the emergent and submergent tidal zones overlap substantially, forming the traditional “intertidal zone”. We conclude by incorporating time and space in the model to illustrate variability in the physical conditions and zonation on littoral shores. The wave:tide physical zonation model is a unifying framework that can facilitate our understanding of physical conditions on littoral shores whether tropical or temperate, marine or lentic. PMID:24109544

Turning the tide: effects of river inflow and tidal amplitude on sandy estuaries in laboratory landscape experiments

NASA Astrophysics Data System (ADS)

Kleinhans, Maarten; Braat, Lisanne; Leuven, Jasper; Baar, Anne; van der Vegt, Maarten; van Maarseveen, Marcel; Markies, Henk; Roosendaal, Chris; van Eijk, Arjan

2016-04-01

Many estuaries formed over the Holocene through a combination of fluvial and coastal influxes, but how estuary planform shape and size depend on tides, wave climate and river influxes remains unclear. Here we use a novel tidal flume setup of 20 m length by 3 m width, the Metronome (http://www.uu.nl/metronome), to create estuaries and explore a parameter space for the simple initial condition of a straight river in sandy substrate. Tidal currents capable of transporting sediment in both the ebb and flood phase because they are caused by periodic tilting of the flume rather than the classic method of water level fluctuation. Particle imaging velocimetry and a 1D shallow flow model demonstrate that this principle leads to similar sediment mobility as in nature. Ten landscape experiments recorded by timelapse overhead imaging and AGIsoft DEMs of the final bed elevation show that absence of river inflow leads to short tidal basins whereas even a minor discharge leads to long convergent estuaries. Estuary width and length as well as morphological time scale over thousands of tidal cycles strongly depend on tidal current amplitude. Paddle-generated waves subdue the ebb delta causing stronger tidal currents in the basin. Bar length-width ratios in estuaries are slightly larger to those in braided rivers in experiments and nature. Mutually evasive ebb- and flood-dominated channels are ubiquitous and appear to be formed by an instability mechanism with growing bar and bifurcation asymmetry. Future experiments will include mud flats and live vegetation.

The anomalous amplification of M2 tide in the Taiwan Strait

NASA Astrophysics Data System (ADS)

Jan, Sen; Chern, Ching-Sheng; Wang, Joe; Chao, Shenn-Yu

2004-04-01

The complex tidal wave propagation pattern in the Taiwan Strait invites parochialism. Along the eastern (Taiwan) boundary of the strait, the anomalous amplification of M2 tide in the middle often led to the parochial view that two tidal waves coming from both ends of the strait collide in the middle, creating wave resonance. Along the western (China) boundary, one sees a southward progressive tidal wave and hence no wave collision. To reconcile, we examine a few solutions of a numerical tidal model below. Both realistic bottom bathymetry and idealized bottom topographies are used to identify dominant mechanism leading to the complex tidal wave propagation. Our process of elimination identifies the wave reflection of southward propagating tidal wave by the deep trench in the southern strait as the true cause responsible for the complex wave propagation pattern.

Computational modeling of unsteady loads in tidal boundary layers

NASA Astrophysics Data System (ADS)

Alexander, Spencer R.

As ocean current turbines move from the design stage into production and installation, a better understanding of oceanic turbulent flows and localized loading is required to more accurately predict turbine performance and durability. In the present study, large eddy simulations (LES) are used to measure the unsteady loads and bending moments that would be experienced by an ocean current turbine placed in a tidal channel. The LES model captures currents due to winds, waves, thermal convection, and tides, thereby providing a high degree of physical realism. Probability density functions, means, and variances of unsteady loads are calculated, and further statistical measures of the turbulent environment are also examined, including vertical profiles of Reynolds stresses, two-point correlations, and velocity structure functions. The simulations show that waves and tidal velocity had the largest impact on the strength of off-axis turbine loads. By contrast, boundary layer stability and wind speeds were shown to have minimal impact on the strength of off- axis turbine loads. It is shown both analytically and using simulation results that either transverse velocity structure functions or two-point transverse velocity spatial correlations are good predictors of unsteady loading in tidal channels.

Synthesis study of an erosion hot spot, Ocean Beach, California

USGS Publications Warehouse

Barnard, Patrick L.; Hansen, Jeff E.; Erikson, Li H.

2012-01-01

A synthesis of multiple coastal morphodynamic research efforts is presented to identify the processes responsible for persistent erosion along a 1-km segment of 7-km-long Ocean Beach in San Francisco, California. The beach is situated adjacent to a major tidal inlet and in the shadow of the ebb-tidal delta at the mouth of San Francisco Bay. Ocean Beach is exposed to a high-energy wave climate and significant alongshore variability in forcing introduced by varying nearshore bathymetry, tidal forcing, and beach morphology (e.g., beach variably backed by seawall, dunes, and bluffs). In addition, significant regional anthropogenic factors have influenced sediment supply and tidal current strength. A variety of techniques were employed to investigate the erosion at Ocean Beach, including historical shoreline and bathymetric analysis, monthly beach topographic surveys, nearshore and regional bathymetric surveys, beach and nearshore grain size analysis, two surf-zone hydrodynamic experiments, four sets of nearshore wave and current experiments, and several numerical modeling approaches. Here, we synthesize the results of 7 years of data collection to lay out the causes of persistent erosion, demonstrating the effectiveness of integrating an array of data sets covering a huge range of spatial scales. The key findings are as follows: anthropogenic influences have reduced sediment supply from San Francisco Bay, leading to pervasive contraction (i.e., both volume and area loss) of the ebb-tidal delta, which in turn reduced the regional grain size and modified wave focusing patterns along Ocean Beach, altering nearshore circulation and sediment transport patterns. In addition, scour associated with an exposed sewage outfall pipe causes a local depression in wave heights, significantly modifying nearshore circulation patterns that have been shown through modeling to be key drivers of persistent erosion in that area.

How tides get dissipated in Saturn? A question probably answerable by Cassni

NASA Astrophysics Data System (ADS)

Luan, Jing

2017-06-01

Tidal dissipation inside a giant planet is important in understanding the orbital evolutions of its natural satellites and perhaps some of the extrasolar giant planets. The tidal dissipation is conventionally parameterized by the tidal quality factor, Q. The corresponding tidal torque declines rapidly with distance adopting constant Q. However, the current fast migration rates of some Saturnian satellites reported by Lainey et al. (2015) conflict this conventional conceptual belief. Alternatively, resonance lock between a satellite and an internal oscillation mode or wave of Saturn, proposed by Fuller et al. (2016), could naturally match the observational migration rates. However, the question still remains to be answered what type of mode or wave is locked with each satellite. There are two candidates for resonance lock, one is gravity mode, and the other is inertial wave attractor. They generate very different gravity acceleration anomaly near the surface of Saturn, which may be distinguishable by the data to be collected by Cassini during its proximal orbits between April and September, 2017. Indicative information about the interior of Saturn may be extracted since the existence of both gravity mode and inertial wave attractor depends on the internal structure of Saturn.

Measurement of tidal and residual currents in the Strait of Hormuz

NASA Astrophysics Data System (ADS)

Azizpour, Jafar; Siadatmousavi, Seyed Mostafa; Chegini, Vahid

2016-09-01

Quantifying the current in the Strait of Hormuz (SH) is vital for understanding the circulation in the Persian Gulf. To measure the current in the strait, four subsurface moorings were deployed at four different stations close to SH from early November 2012 to the end of January 2013. Tidal current were dominant in the SH. The tides in the SH were complex partially standing waves and the dominant pattern varied from being primarily semi-diurnal to diurnal. The phase difference between tidal constituents of current and sea level elevation time series was used as an index to show the partially progressive wave pattern inside the study area. At mooring positions 3 and 4, located to the left of SH, the phase differences were close to 160° and 100°, respectively. It indicates partially progressive waves in opposite direction at these stations. K1 and M2 were the two main constituents at all stations inside the study area. At surface, the magnitude of semi-major axis of ellipses for M2 constituent was larger than corresponding value for K1 whereas at the bottom layer, the opposite pattern was observed. The M2 rotary coefficients at mooring 1 illustrated that current vector at the bottom layer rotated in opposite direction compared to current vectors at the middle and surface layers. The rotation was counterclockwise in the bottom layer, while it was clockwise in the surface and middle layers.

Modeling influence of tide stages on forecasts of the 2010 Chilean tsunami

NASA Astrophysics Data System (ADS)

Uslu, B. U.; Chamberlin, C.; Walsh, D.; Eble, M. C.

2010-12-01

The impact of the 2010 Chilean tsunami is studied using the NOAA high-resolution tsunami forecast model augmented to include modeled tide heights in addition to deep-water tsunami propagation as boundary-condition input. The Chilean tsunami was observed at the Los Angeles tide station at mean low water, Hilo at low, Pago Pago at mid tide and Wake Island near high tide. Because the tsunami arrived at coastal communities at a representative variety of tide stages, 2010 Chile tsunami provides opportunity to study the tsunami impacts at different tide levels to different communities. The current forecast models are computed with a constant tidal stage, and this study evaluates techniques for adding an additional varying predicted tidal component in a forecasting context. Computed wave amplitudes, wave currents and flooding are compared at locations around the Pacific, and the difference in tsunami impact due to tidal stage is studied. This study focuses on how tsunami impacts vary with different tide levels, and helps us understand how the inclusion of tidal components can improve real-time forecast accuracy.

A Multiscale Nested Modeling Framework to Simulate the Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves

DTIC Science & Technology

2015-09-30

We aim at understanding the impact of tidal , seasonal, and mesoscale variability of the internal wave field and how it influences the surface waves ...Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves Lian Shen St. Anthony Falls Laboratory and Department of Mechanical...on studying surface gravity wave evolution and spectrum in the presence of surface currents caused by strongly nonlinear internal solitary waves

Sediment Dynamics in Shallow Tidal Landscapes: The Role of Wind Waves and Tidal Currents

NASA Astrophysics Data System (ADS)

Carniello, L.; D'Alpaos, A.

2014-12-01

A precise description of sediment dynamics (resuspension and re-distribution of sediments) is crucial when investigating the long term evolution of the different morphological entities characterizing tidal landscapes. It has been demonstrated that wind waves are the main responsible for sediment resuspension in shallow micro-tidal lagoons where tidal currents, which produce shear stresses large enough to carry sediments into suspension only within the main channels, are mainly responsible for sediment redistribution. A mathematical model has been developed to describe sediment entrainment, transport and deposition due to the combined effect of tidal currents and wind waves in shallow lagoons considering both cohesive and non-cohesive sediments. The model was calibrated and tested using both in situ point observations and turbidity maps obtained analyzing satellite images. Once calibrated the model can integrate the high temporal resolution of point observations with the high spatial resolution of remote sensing, overcoming the intrinsic limitation of these two types of observations. The model was applied to the specific test case of the Venice lagoon simulating an entire year (2005) which was shown to be a "representative" year for wind and tide characteristics. The time evolution of the computed total bottom shear stresses (BSS) and suspended sediment concentration (SSC) was analyzed on the basis of a "Peaks Over Threshold" method once a critical value for shear stress and turbidity were chosen. The analyses of the numerical results enabled us to demonstrate that resuspension events can be modeled as marked Poisson processes: interarrival time, intensity of peak excesses and duration being exponentially distributed random variable. The probability distributions of the interarrival time of overthreshold exceedances in both BSS and SSC as well as their intensity and duration can be used in long-term morphodynamic studies to generate synthetic series statistically equivalent to real sequences through which MonteCarlo realizations of relevant morphological evolutions can be computed.

Wave exposure of Corte Madera Marsh, Marin County, California-a field investigation

USGS Publications Warehouse

Lacy, Jessica R.; Hoover, Daniel J.

2011-01-01

Tidal wetlands provide valuable habitat, are an important source of primary productivity, and can help to protect the shoreline from erosion by attenuating approaching waves. These functions are threatened by the loss of tidal marshes, whether due to erosion, sea-level rise, or land-use practices. Erosion protection by wetlands is expected to vary geographically, because wave attenuation in marshes depends on vegetation type, density, and height and wave attenuation over mudflats depends on slope and sediment properties. In macrotidal northern European marshes, a 50 percent reduction in wave height within tens of meters of vegetated salt marsh has been observed. This study was designed to evaluate the role of mudflats and marshes in attenuating waves at a site in San Francisco Bay. In prehistoric times, the shoreline of San Francisco Bay was ringed with tidal wetlands, with mudflats at lower elevations and marshes above. Most of the marshes around the Bay emerged 2,000-4,000 years ago, after the rate of sea-level rise slowed to approximately 1 mm/year. Approximately 80 percent of the acreage of tidal marsh and 40 percent of the acreage of tidal mudflats in San Francisco Bay have been lost to filling and draining since 1800. Tidal wetlands are particularly susceptible to impacts from sea-level rise because the vegetation at each elevation is adapted to a specific tidal-inundation regime. The maintenance of suitable marsh-plain elevations depends on a supply of sediment that can keep up with the rate of sea-level rise. Sea-level rise, which according to recent projections may reach 75 to 190 cm by the year 2100, poses a significant threat to wetlands in San Francisco Bay, where landward migration is frequently impossible due to urbanization of the adjacent landscape. In this study, we collected data in Corte Madera Bay and Marsh to determine whether, and to what degree, waves are attenuated as they transit the Bay and, during high tides, the marsh. Corte Madera Bay was selected as a study site because of its exposure to wind waves, as well as its history of shoreline erosion and marsh restoration and monitoring. Data were collected in the winter of 2010, along a cross-shore transect extending from offshore of the subtidal mudflats into the tidal marsh. This study forms part of the Innovative Wetland Adaptation in the Lower Corte Madera Creek Watershed Project initiated by the Bay Conservation and Development Commission (BCDC) (http://www.bcdc.ca.gov/planning/climate_change/WetlandAdapt.shtml). Objectives- This study was designed to address the following questions: * What are the characteristics of waves and currents in the study area, and how do they vary over time? * Do wave heights or orbital velocities decrease, or wave periods change, as waves pass over the mudflats? * Do wave heights decrease, or wave periods change, as waves pass over the marsh?

Suspended-sediment flux and retention in a backwater tidal slough complex near the landward boundary of an estuary

USGS Publications Warehouse

Morgan-King, Tara L.; Schoellhamer, David H.

2013-01-01

Backwater tidal sloughs are commonly found at the landward boundary of estuaries. The Cache Slough complex is a backwater tidal region within the Upper Sacramento–San Joaquin Delta that includes two features that are relevant for resource managers: (1) relatively high abundance of the endangered fish, delta smelt (Hypomesus transpacificus), which prefers turbid water and (2) a recently flooded shallow island, Liberty Island, that is a prototype for habitat restoration. We characterized the turbidity around Liberty Island by measuring suspended-sediment flux at four locations from July 2008 through December 2010. An estuarine turbidity maximum in the backwater Cache Slough complex is created by tidal asymmetry, a limited tidal excursion, and wind-wave resuspension. During the study, there was a net export of sediment, though sediment accumulates within the region from landward tidal transport during the dry season. Sediment is continually resuspended by both wind waves and flood tide currents. The suspended-sediment mass oscillates within the region until winter freshwater flow pulses flush it seaward. The hydrodynamic characteristics within the backwater region such as low freshwater flow during the dry season, flood tide dominance, and a limited tidal excursion favor sediment retention.

Beach protection by a system of permeable groins

NASA Astrophysics Data System (ADS)

Boczar-Karakiewicz, B.; Romanczyk, W.; Roy, N.

2002-12-01

A new type of permeable groin (called System of Groins Maltec-Savard - SGMS) has been installed at three eroded sites located in the coastal area on the north shore of the St. Lawrence, Quebec, Canada. In this area, the narrow sandy beaches with sandy or sand-silty cliff of variable height (10-15~m) are exposed to obliquely incident waves arriving from both west (summer) and east (autumn), and to tidal currents (maximum tidal rate is 4.3~m). The periods of summer waves equal 3-5~s, with wave heights of about 0.4-0.7~m. In the autumn, major storm waves reach periods of up to 7-10~s, with wave heights of 1.0-1.2~m. The new groins are sediment traps formed by a central double and permeable groin with several smaller lateral, groins installed on one or both sides of the central groin (Boczar-Karakiewicz et al., 2001). The permeable central and lateral groins are structured by inserting double ranges of wooden piles (diameter of about 10 cm). The space between the ranges of piles (some 0.8~m wide) is filled with tree branches (e.g., the top parts of pine trees, a waste product of the local forest industry). A permeable grid covering the top of the groins forms a cage that holds the branches in place. The lateral groins, are identical but much shorter than the central groin. The whole system dissipates the incident energy of wave- and tidally-generated currents and causes accretion of sand transported by these currents. The GSMS also allows the by-pass of some sediment to adjacent zones without groins. Observations and results of measurements from three experiments field show that: (1) a sandy beach in front of a coastal cliff secures its stability and attenuates the erosion caused by waves and tidal currents; (2) permeability and flexibility of the SGMS causes the accretion of sediment in the protected area without erosion in the neighboring zones; (3) the SGMS does not generate wave reflection and any secondary current; (4) the materials of the groins are easily available, and the cost is low (waste material of the local forest industry); (5) the construction is simple and can be carried out by low-skilled labor force. Boczar-Karakiewicz, B., W. Romanczyk, N. Roy, N. Pelletier, L. Maltec and J.-P. Savard. 2001. New method of beach protection adapted to coastal zones of the estuary of the Saint Lawrence river, Quebec, Canada. Proc. Can. Coast. Conf., Quebec, QC, Canada: 201-214 (in French).

33 CFR 165.1325 - Regulated Navigation Areas; Bars Along the Coasts of Oregon and Washington.

Code of Federal Regulations, 2010 CFR

2010-07-01

..., wave period, and tidal currents. When a bar is restricted, the operation of recreational and... passengers. (13) Unsafe condition exists when the wave height within a regulated navigation area identified in paragraph (a) of this section is equal to or greater than the maximum wave height determined by...

The influence of neap-spring tidal variation and wave energy on sediment flux in salt marsh tidal creeks

USGS Publications Warehouse

Lacy, Jessica; Ferner, Matthew C.; Callaway, John C.

2018-01-01

Sediment flux in marsh tidal creeks is commonly used to gage sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended-sediment concentration (SSC), velocity, and depth were measured near the mouths of two tidal creeks during three six-to-ten-week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally-averaged suspended-sediment flux (SSF) in the tidal creeks decreased with increasing tidal energy, and SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF measured during the deployments. During ebb tides following the highest tides, velocities exceeded 1 m/s in the narrow tidal creeks, resulting in negative tidally-averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally-averaged SSF was positive in wavey conditions with moderate tides. Spring-tide sediment export was about 50% less at a station 130 m further up the tidal creek than at the creek mouth. The negative tidally-averaged water flux near the creek mouth during spring tides indicates that in the lower marsh, some of the water flooding directly across the bay--marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well.

Time scales of circulation and mixing processes of San Francisco Bay waters

USGS Publications Warehouse

Walters, R.A.; Cheng, R.T.; Conomos, T.J.

1985-01-01

Conceptual models for tidal period and low-frequency variations in sea level, currents, and mixing processes in the northern and southern reaches of San Francisco Bay describe the contrasting characteristics and dissimilar processes and rates in these embayments: The northern reach is a partially mixed estuary whereas the southern reach (South Bay) is a tidally oscillating lagoon with density-driven exchanges with the northern reach. The mixed semidiurnal tides are mixtures of progressive and standing waves. The relatively simple oscillations in South Bay are nearly standing waves, with energy propagating down the channels and dispersing into the broad shoal areas. The tides of the northern reach have the general properties of a progressive wave but are altered at the constriction of the embayments and gradually change in an upstream direction to a mixture of progressive and standing waves. The spring and neap variations of the tides are pronounced and cause fortnightly varying tidal currents that affect mixing and salinity stratification in the water column. Wind stress on the water surface, freshwater inflow, and tidal currents interacting with the complex bay configuration are the major local forcing mechanisms creating low-frequency variations in sea level and currents. These local forcing mechanisms drive the residual flows which, with tidal diffusion, control the water-replacement rates in the estuary. In the northern reach, the longitudinal density gradient drives an estuarine circulation in the channels, and the spatial variation in tidal amplitude creates a tidally-driven residual circulation. In contrast, South Bay exhibits a balance between wind-driven circulation and tidally-driven residual circulation for most of the year. During winter, however, there can be sufficient density variations to drive multilayer (2 to 3) flows in the channel of South Bay. Mixing models (that include both diffusive and dispersive processes) are based on time scales associated with salt variations at the boundaries and those associated with the local forcing mechanisms, while the spatial scales of variations are dependent upon the configuration of the embayments. In the northern reach, where the estuarine circulation is strong, the salt flux is carried by the mean advection of the mean salt field. Where large salinity gradients are present, the tidal correlation part of the salt flux is of the same order as the advective part. Our knowledge of mixing and exchange rates in South Bay is poor. As this embayment is nearly isohaline, the salt flux is dominated entirely by the mean advection of the mean salt field. During and after peaks in river discharge, water mixing becomes more dynamic, with a strong density-driven current creating a net exchange of both water mass and salt. These exchanges are stronger during neap tides. Residence times of the water masses vary seasonally and differ between reaches. In the northern reach, residence times are on the order of days for high winter river discharge and of months for summer periods. The residence times for South Bay are fairly long (on the order of several months) during summer, and typically shorter (less than a month) during winter when density-driven exchanges occur. ?? 1985 Dr W. Junk Publishers.

Are Wave and Tidal Energy Plants New Green Technologies?

PubMed

Douziech, Mélanie; Hellweg, Stefanie; Verones, Francesca

2016-07-19

Wave and tidal energy plants are upcoming, potentially green technologies. This study aims at quantifying their various potential environmental impacts. Three tidal stream devices, one tidal range plant and one wave energy harnessing device are analyzed over their entire life cycles, using the ReCiPe 2008 methodology at midpoint level. The impacts of the tidal range plant were on average 1.6 times higher than the ones of hydro-power plants (without considering natural land transformation). A similar ratio was found when comparing the results of the three tidal stream devices to offshore wind power plants (without considering water depletion). The wave energy harnessing device had on average 3.5 times higher impacts than offshore wind power. On the contrary, the considered plants have on average 8 (wave energy) to 20 (tidal stream), or even 115 times (tidal range) lower impact than electricity generated from coal power. Further, testing the sensitivity of the results highlighted the advantage of long lifetimes and small material requirements. Overall, this study supports the potential of wave and tidal energy plants as alternative green technologies. However, potential unknown effects, such as the impact of turbulence or noise on marine ecosystems, should be further explored in future research.

International Symposium on Wave and Tidal Energy, 2nd, St. John's College, Cambridge, England, September 23-25, 1981, Proceedings

NASA Astrophysics Data System (ADS)

Stephens, H. S.; Stapleton, C. A.

Topics discussed include wave power device interactions, the mathematical modeling of tidal power, and wave power with air turbines. Particular attention is given to the hydrodynamic characteristics of the Bristol Cylinder, the Strangford Lough tidal energy project, and the Foilpropeller for wave power propulsion. Consideration is also given to a submerged oscillating water column device, models of wave energy transformation near a coast, and the environmental implications of tidal power.

Modeled and Observed Transitions Between Rip Currents and Alongshore Flows

NASA Astrophysics Data System (ADS)

Moulton, M.; Elgar, S.; Warner, J. C.; Raubenheimer, B.

2014-12-01

Predictions of rip currents, alongshore currents, and the temporal transitions between these circulation patterns are important for swimmer safety and for estimating the transport of sediments, biota, and pollutants in the nearshore. Here, field observations are combined with hydrodynamic modeling to determine the dominant processes that lead rip currents to turn on and off with changing waves, bathymetry, and tidal elevation. Waves, currents, mean sea levels, and bathymetry were measured near and within five shore-perpendicular channels (on average 2-m deep, 30-m wide) that were dredged with the propellers of a landing craft at different times on a long straight Atlantic Ocean beach near Duck, NC in summer 2012. The circulation was measured for a range of incident wave conditions and channel sizes, and included rapid transitions between strong (0.5 to 1 m/s) rip current jets flowing offshore through the channels and alongshore currents flowing across the channels with no rip currents. Meandering alongshore currents (alongshore currents combined with an offshore jet at the downstream edge of the channel) also were observed. Circulation patterns near and within idealized rip channels simulated with COAWST (a three-dimensional phase-averaged model that couples ROMS and SWAN) are compared with the observations. In addition, the model is used to investigate the hydrodynamic response to a range of wave conditions (angle, height, period) and bathymetries (channel width, depth, and length; tidal elevations; shape of sandbar or terrace). Rip current speeds are largest for the deepest perturbations, and decrease as incident wave angles become more oblique. For obliquely incident waves, the rip currents are shifted in the direction of the alongshore flow, with an increasing shift for increasing alongshore current speed or increasing bathymetric perturbation depth.

Three-Dimensional Dynamics of Baroclinic Tides Over a Seamount

NASA Astrophysics Data System (ADS)

Vlasenko, Vasiliy; Stashchuk, Nataliya; Nimmo-Smith, W. Alex M.

2018-02-01

The Massachusetts Institute of Technology general circulation model is used for the analysis of baroclinic tides over Anton Dohrn Seamount (ADS), in the North Atlantic. The model output is validated against in situ data collected during the 136th cruise of the RRS "James Cook" in May-June 2016. The observational data set includes velocity time series recorded at two moorings as well as temperature, salinity, and velocity profiles collected at 22 hydrological stations. Synthesis of observational and model data enabled the reconstruction of the details of baroclinic tidal dynamics over ADS. It was found that the baroclinic tidal waves are generated in the form of tidal beams radiating from the ADS periphery to its center, focusing tidal energy in a surface layer over the seamount's summit. This energy focusing enhances subsurface water mixing and the local generation of internal waves. The tidal beams interacting with the seasonal pycnocline generate short-scale internal waves radiating from the ADS center. An important ecological outcome from this study concerns the pattern of residual currents generated by tides. The rectified flows over ADS have the form of a pair of dipoles, cyclonic and anticyclonic eddies located at the seamount's periphery. These eddies are potentially an important factor in local larvae dispersion and their escape from ADS.

Thermography of the New River Inlet plume and nearshore currents

NASA Astrophysics Data System (ADS)

Chickadel, C.; Jessup, A.

2012-12-01

As part of the DARLA and RIVET experiments, thermal imaging systems mounted on a tower and in an airplane captured water flow in the New River Inlet, NC, USA. Kilometer-scale, airborne thermal imagery of the inlet details the ebb flow of the estuarine plume water mixing with ocean water. Multiple fronts, corresponding to the preferred channels through the ebb tidal delta, are imaged in the aerial data. A series of internal fronts suggest discreet sources of the tidal plume that vary with time. Focused thermal measurements made from a tower on the south side of the inlet viewed an area within a radius of a few hundred meters. Sub-meter resolution video from the tower revealed fine-scale flow features and the interaction of tidal exchange and wave-forced surfzone currents. Using the tower and airborne thermal image data we plan to provide geophysical information to compare with numerical models and in situ measurements made by other investigators. From the overflights, we will map the spatial and temporal extent of the estuarine plume to correlate with tidal phase and local wind conditions. From the tower data, we will investigate the structure of the nearshore flow using a thermal particle image velocimetry (PIV) technique, which is based on tracking motion of the surface temperature patterns. Long term variability of the mean and turbulent two-dimensional PIV currents will be correlated to local wave, tidal, and wind forcing parameters.

Changes in surfzone morphodynamics driven by multi-decadel contraction of a large ebb-tidal delta

USGS Publications Warehouse

Hansen, Jeff E.; Elias, Edwin; Barnard, Patrick L.; Barnard, P.L.; Jaffee, B.E.; Schoellhamer, D.H.

2013-01-01

The impact of multi-decadal, large-scale deflation (76 million m3 of sediment loss) and contraction (~ 1 km) of a 150 km2 ebb-tidal delta on hydrodynamics and sediment transport at adjacent Ocean Beach in San Francisco, CA (USA), is examined using a coupled wave and circulation model. The model is forced with representative wave and tidal conditions using recent (2005) and historic (1956) ebb-tidal delta bathymetry data sets. Comparison of the simulations indicates that along north/south trending Ocean Beach the contraction and deflation of the ebb-tidal delta have resulted in significant differences in the flow and sediment dynamics. Between 1956 and 2005 the transverse bar (the shallow attachment point of the ebb-tidal delta to the shoreline) migrated northward ~ 1 km toward the inlet while a persistent alongshore flow and transport divergence point migrated south by ~ 500 m such that these features now overlap. A reduction in tidal prism and sediment supply over the last century has resulted in a net decrease in offshore tidal current-generated sediment transport at the mouth of San Francisco Bay, and a relative increase in onshore-directed wave-driven transport toward the inlet, accounting for the observed contraction of the ebb-tidal delta. Alongshore migration of the transverse bar and alongshore flow divergence have resulted in an increasing proportion of onshore migrating sediment from the ebb-tidal delta to be transported north along the beach in 2005 versus south in 1956. The northerly migrating sediment is then trapped by Pt. Lobos, a rocky headland at the northern extreme of the beach, consistent with the observed shoreline accretion in this area. Conversely, alongshore migration of the transverse bar and divergence point has decreased the sediment supply to southern Ocean Beach, consistent with the observed erosion of the shoreline in this area. This study illustrates the utility of applying a high-resolution coupled circulation-wave model for understanding coastal response to large-scale bathymetric changes over multi-decadal timescales, common to many coastal systems adjacent to urbanized estuaries and watersheds worldwide.

33 CFR 165.1325 - Regulated Navigation Areas; Bars Along the Coasts of Oregon and Washington.

Code of Federal Regulations, 2013 CFR

2013-07-01

... type of vessel, sea state, winds, wave period, and tidal currents. When a bar is restricted, the... representative and carrying not more than six passengers. (13) Unsafe condition exists when the wave height... than the maximum wave height determined by the formula L/10 + F = W where: L = Overall length of a...

33 CFR 165.1325 - Regulated Navigation Areas; Bars Along the Coasts of Oregon and Washington.

Code of Federal Regulations, 2014 CFR

2014-07-01

... type of vessel, sea state, winds, wave period, and tidal currents. When a bar is restricted, the... representative and carrying not more than six passengers. (13) Unsafe condition exists when the wave height... than the maximum wave height determined by the formula L/10 + F = W where: L = Overall length of a...

33 CFR 165.1325 - Regulated Navigation Areas; Bars Along the Coasts of Oregon and Washington.

Code of Federal Regulations, 2012 CFR

2012-07-01

... type of vessel, sea state, winds, wave period, and tidal currents. When a bar is restricted, the... representative and carrying not more than six passengers. (13) Unsafe condition exists when the wave height... than the maximum wave height determined by the formula L/10 + F = W where: L = Overall length of a...

33 CFR 165.1325 - Regulated Navigation Areas; Bars Along the Coasts of Oregon and Washington.

Code of Federal Regulations, 2011 CFR

2011-07-01

... type of vessel, sea state, winds, wave period, and tidal currents. When a bar is restricted, the... representative and carrying not more than six passengers. (13) Unsafe condition exists when the wave height... than the maximum wave height determined by the formula L/10 + F = W where: L = Overall length of a...

Assessing the vertical structure of baroclinic tidal currents in a global model

NASA Astrophysics Data System (ADS)

Timko, Patrick; Arbic, Brian; Scott, Robert

2010-05-01

Tidal forcing plays an important role in many aspects of oceanography. Mixing, transport of particulates and internal wave generation are just three examples of local phenomena that may depend on the strength of local tidal currents. Advances in satellite altimetry have made an assessment of the global barotropic tide possible. However, the vertical structure of the tide may only be observed by deployment of instruments throughout the water column. Typically these observations are conducted at pre-determined depths based upon the interest of the observer. The high cost of such observations often limits both the number and the length of the observations resulting in a limit to our knowledge of the vertical structure of tidal currents. One way to expand our insight into the baroclinic structure of the ocean is through the use of numerical models. We compare the vertical structure of the global baroclinic tidal velocities in 1/12 degree HYCOM (HYbrid Coordinate Ocean Model) to a global database of current meter records. The model output is a subset of a 5 year global simulation that resolves the eddying general circulation, barotropic tides and baroclinic tides using 32 vertical layers. The density structure within the simulation is both vertically and horizontally non-uniform. In addition to buoyancy forcing the model is forced by astronomical tides and winds. We estimate the dominant semi-diurnal (M2), and diurnal (K1) tidal constituents of the model data using classical harmonic analysis. In regions where current meter record coverage is adequate, the model skill in replicating the vertical structure of the dominant diurnal and semi-diurnal tidal currents is assessed based upon the strength, orientation and phase of the tidal ellipses. We also present a global estimate of the baroclinic tidal energy at fixed depths estimated from the model output.

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-05-09

ISS013-E-16599 (9 May 2006) --- Wave sets and tidal currents in the Gulf of California are featured in this image photographed by an Expedition 13 crewmember on the International Space Station. In this image, sunglint off the Gulf of California gives the water a silver-gray appearance rather than the usual azure blue color. The sunglint allows us to see several active features which would not be visible otherwise. In this view of Punta Perihuete, Mexico we can see three major features: biological or man-made oils floating on the surface; the out-going tidal current; and complex wave patterns. The oils on the surface are recognizable as light grey, curved and variable-width streamers shaped by the local winds and currents. Plankton, fish, natural oil seeps and boats dumping bilges are all potential sources for these oils.

Tides and deltaic morphodynamics

NASA Astrophysics Data System (ADS)

Plink-Bjorklund, Piret

2016-04-01

Tide-dominated and tide-influenced deltas are not widely recognized in the ancient record, despite the numerous modern and Holocene examples, including eight of the twelve modern largest deltas in the world, like the Ganges-Brahmaputra, Amazon, Chang Jiang, and Irrawadi. Furthermore, tide-dominated or tide-influenced deltas are suggested to be more common in inner-shelf or embayment settings rather than close to or at a shelf edge, primarily because wave energy is expected to be higher and tidal energy lower in outer shelf and shelf-edge areas. Thus, most shelf-edge deltas are suggested to be fluvial or wave dominated. However, there are ancient examples of tide-influenced shelf-edge deltas, indicating that the controls on tidal morphodynamics in deltas are not yet well understood. This paper asks the following questions: (1) How do tides influence delta deposition, beyond creating recognizable tidal facies? (2) Does tidal reworking create specific geometries in delta clinoforms? (3) Does tidal reworking change progradation rates of deltas? (4) Is significant tidal reworking of deltas restricted to inner-shelf deltas only? (5) What are the conditions at which deltas may be tidally influenced or tide-dominated in outer-shelf areas or at the shelf edge? (6) What are the main morphodynamic controls on the degree of tidal reworking of deltas? The paper utilizes a dataset of multiple ancient and modern deltas, situated both on the shelf and shelf edge. We show that beyond the commonly recognized shore-perpendicular morphological features and the recognizable tidal facies, the main effects of tidal reworking of deltas are associated with delta clinoform morphology, morphodynamics of delta lobe switching, delta front progradation rates, and the nature of the delta plain. Strong tidal influence is here documented to promote subaqueous, rapid progradation of deltas, by efficiently removing sediment from river mouth and thus reducing mouth bar aggradation and fluvial delta plain construction rates. Such subaqueous progradation of the delta front is decoupled from shoreline progradation. The delta plain of such tide-dominated deltas consists of a few distributary channels and tidal flats on top of the emerged tidal bars. The delta front clinoforms become gentler and longer, as ebb tidal currents together with river effluent efficiently transport sediment to the basin. Tide-dominated deltas tend to maintain a funnel shape and show low lobe switching rates, compared to fluvial-dominated and tide-influenced deltas. The funnel and thus river mouth position is further stabilized by fine-grained sediment accumulation on marginal tidal flats due to the flood current sediment transport. However, all these effect weaken as the deltas prograde to the shelf edge, due to the loss of vertical (and lateral) restriction and tidal amplification. Here significant tidal reworking tends to be restricted to topographic irregularities, caused by incision, delta-lobe or mouth bar deposition and avulsions, or tectonic processes. The role of such topographic restrictions is twofold, by reducing wave energy and amplifying tidal energy.

Validation of a coupled wave-flow model in a high-energy setting: the mouth of the Columbia River

USGS Publications Warehouse

Elias, Edwin P.L.; Gelfenbaum, Guy R.; van der Westhuysen, André J.

2012-01-01

 A monthlong time series of wave, current, salinity, and suspended-sediment measurements was made at five sites on a transect across the Mouth of Columbia River (MCR). These data were used to calibrate and evaluate the performance of a coupled hydrodynamic and wave model for the MCR based on the Delft3D modeling system. The MCR is a dynamic estuary inlet in which tidal currents, river discharge, and wave-driven currents are all important. Model tuning consisted primarily of spatial adjustments to bottom drag coefficients. In combination with (near-) default parameter settings, the MCR model application is able to simulate the dominant features in the tidal flow, salinity and wavefields observed in field measurements. The wave-orbital averaged method for representing the current velocity profile in the wave model is considered the most realistic for the MCR. The hydrodynamic model is particularly effective in reproducing the observed vertical residual and temporal variations in current structure. Density gradients introduce the observed and modeled reversal of the mean flow at the bed and augment mean and peak flow in the upper half of the water column. This implies that sediment transport during calmer summer conditions is controlled by density stratification and is likely net landward due to the reversal of flow near the bed. The correspondence between observed and modeled hydrodynamics makes this application a tool to investigate hydrodynamics and associated sediment transport.

Validation of a coupled wave-flow model in a high-energy setting: The mouth of the Columbia River

NASA Astrophysics Data System (ADS)

Elias, Edwin P. L.; Gelfenbaum, Guy; Van der Westhuysen, André J.

2012-09-01

A monthlong time series of wave, current, salinity, and suspended-sediment measurements was made at five sites on a transect across the Mouth of Columbia River (MCR). These data were used to calibrate and evaluate the performance of a coupled hydrodynamic and wave model for the MCR based on the Delft3D modeling system. The MCR is a dynamic estuary inlet in which tidal currents, river discharge, and wave-driven currents are all important. Model tuning consisted primarily of spatial adjustments to bottom drag coefficients. In combination with (near-) default parameter settings, the MCR model application is able to simulate the dominant features in the tidal flow, salinity and wavefields observed in field measurements. The wave-orbital averaged method for representing the current velocity profile in the wave model is considered the most realistic for the MCR. The hydrodynamic model is particularly effective in reproducing the observed vertical residual and temporal variations in current structure. Density gradients introduce the observed and modeled reversal of the mean flow at the bed and augment mean and peak flow in the upper half of the water column. This implies that sediment transport during calmer summer conditions is controlled by density stratification and is likely net landward due to the reversal of flow near the bed. The correspondence between observed and modeled hydrodynamics makes this application a tool to investigate hydrodynamics and associated sediment transport.

Research on the unsteady hydrodynamic characteristics of vertical axis tidal turbine

NASA Astrophysics Data System (ADS)

Zhang, Xue-wei; Zhang, Liang; Wang, Feng; Zhao, Dong-ya; Pang, Cheng-yan

2014-03-01

The unsteady hydrodynamic characteristics of vertical axis tidal turbine are investigated by numerical simulation based on viscous CFD method. The starting mechanism of the turbine is revealed through analyzing the interaction of its motion and dynamics during starting process. The operating hydrodynamic characteristics of the turbine in wave-current condition are also explored by combining with the linear wave theory. According to possible magnification of the cyclic loads in the maximum power tracking control of vertical axis turbine, a novel torque control strategy is put forward, which can improve the structural characteristics significantly without effecting energy efficiency.

Rapid Assessment of Wave Height Transformation through a Tidal Inlet via Radar Remote Sensing

NASA Astrophysics Data System (ADS)

Díaz Méndez, G.; Haller, M. C.; Raubenheimer, B.; Elgar, S.; Honegger, D.

2014-12-01

Radar has the potential to enable temporally and spatially dense, continuous monitoring of waves and currents in nearshore environments. If quantitative relationships between the remote sensing signals and the hydrodynamic parameters of interest can be found, remote sensing techniques can mitigate the challenges of continuous in situ sampling and possibly enable a better understanding of wave transformation in areas with strongly inhomogeneous along and across-shore bathymetry, currents, and dissipation. As part of the DARLA experiment (New River Inlet, NC), the accuracy of a rapid assessment of wave height transformation via radar remote sensing is tested. Wave breaking events are identified in the radar image time series (Catalán et al. 2011). Once the total number of breaking waves (per radar collection) is mapped throughout the imaging domain, radar-derived bathymetry and wave frequency are used to compute wave breaking dissipation (Janssen and Battjes 2007). Given the wave breaking dissipation, the wave height transformation is calculated by finding an inverse solution to the 1D cross-shore energy flux equation (including the effect of refraction). The predicted wave height transformation is consistent (correlation R > 0.9 and rmse as low as 0.1 m) with the transformation observed with in situ sensors in an area of complex morphology and strong (> 1 m/s) tidal currents over a nine-day period. The wave forcing (i.e., radiation stress gradients) determined from the remote sensing methodology will be compared with values estimated with in situ sensors. Funded by ONR and ASD(R&E)

Modern sedimentary environments in a large tidal estuary, Delaware Bay

USGS Publications Warehouse

Knebel, H.J.

1989-01-01

Data from an extensive grid of sidescan-sonar records reveal the distribution of sedimentary environments in the large, tidally dominated Delaware Bay estuary. Bathymetric features of the estuary include large tidal channels under the relatively deep (> 10 m water depth) central part of the bay, linear sand shoals (2-8 m relief) that parallel the sides of the tidal channels, and broad, low-relief plains that form the shallow bay margins. The two sedimentary environments that were identified are characterized by either (1) bedload transport and/or erosion or (2) sediment reworking and/or deposition. Sand waves and sand ribbons, composed of medium to coarse sands, define sites of active bedload transport within the tidal channels and in gaps between the linear shoals. The sand waves have spacings that vary from 1 to 70 m, amplitudes of 2 m or less, and crestlines that are usually straight. The orientations of the sand waves and ribbons indicate that bottom sediment movement may be toward either the northwest or southeast along the trends of the tidal channels, although sand-wave asymmetry indicates that the net bottom transport is directed northwestward toward the head of the bay. Gravelly, coarse-grained sediments, which appear as strongly reflective patterns on the sonographs, are also present along the axes and flanks of the tidal channels. These coarse sediments are lag deposits that have developed primarily where older strata were eroded at the bay floor. Conversely, fine sands that compose the linear shoals and muddy sands that cover the shallow bay margins appear mainly on the sonographs either as smooth featureless beds that have uniform light to moderate shading or as mosaics of light and dark patches produced by variations in grain size. These acoustic and textural characteristics are the result of sediment deposition and reworking. Data from this study (1) support the hypothesis that bed configurations under deep tidal flows are functions of current velocity, sediment size, and depth; (2) suggest criteria that could be used to distinguish between open estuarine tidal deposits in the geologic record; and (3) provide a guide to future utilization of the bay floor. ?? 1989.

Marine and Hydrokinetic Data | Geospatial Data Science | NREL

Science.gov Websites

. wave energy resource using a 51-month Wavewatch III hindcast database developed by the National Database The U.S. Department of Energy's Marine and Hydrokinetic Technology Database provides information database includes wave, tidal, current, and ocean thermal energy and contains information about energy

Influence of Waves and Tides on Upper Slope Turbidity Currents and their Deposits: An Outcrop and Laboratory Study

NASA Astrophysics Data System (ADS)

Daniller-Varghese, M. S.; Smith, E.; Mohrig, D. C.; Goudge, T. A.; Hassenruck-Gudipati, H. J.; Koo, W. M.; Mason, J.; Swartz, J. M.; Kim, J.

2017-12-01

Research on interactions of turbidity currents with waves and tides highlight both their importance and complexity. The Elkton Siltstone at Cape Arago, Oregon, USA, preserves rhythmically bedded deposits that we interpret as the product of tidally modified hyperpycnal flows under the influence of water-surface waves. Evidence for the interpretation of tidal influence is taken from couplet thickness measurements consistent with semidiurnal tides arranged into monthly cycles. These deposits were likely sourced from suspended-sediment laden river plumes; thinner, finer-grained beds represent deposition during flood tide, and thicker, coarser-grained beds represent deposition during ebb tide. Sedimentary structures within the rhythmites change from proximal to distal sections, but both sections preserve combined-flow bedforms within the beds, implying wave influence. Our paleo-topographic reconstruction has the proximal section located immediately down-dip of the shelf slope-break and the distal section located 1.5km further offshore in 125m greater water depth. We present experimental results from wave-influenced turbidity currents calling into question the interpretation that combined-flow bedforms necessarily require deposition at or above paleo-wave base. Turbidity currents composed of quartz silt and very fine sand were released into a 10m long, 1.2m deep tank. Currents ran down a 9-degree ramp with a motor driven wave-maker positioned at the distal end of the tank. The currents interacted with the wave field as they travelled downslope into deeper water. While oscillatory velocities measured within the wave-influenced turbidity currents decreased with distance downslope, the maximum oscillatory velocities measured in the combined-flow currents at depth were five to six times larger than those measured under a wave field without turbidity currents. These results suggest that combined-flow turbidity currents can transmit oscillating-flow signals beneath the effective wave base. Bed thicknesses, grain-size data, sedimentary structures and fabrics measured in the rhythmically bedded, combined-flow turbidites of the Elkton Siltstone will be interpreted in the context of these experiments.

Effects of Internal Waves on Sound Propagation in the Shallow Waters of the Continental Shelves

DTIC Science & Technology

2016-09-01

experiment area were largely generated by tidal forcing. Compared to simulations without internal waves , simulations accounting for the effects of...internal waves in the experiment area were largely generated by tidal forcing. Compared to simulations without internal waves , simulations accounting for...IN THE SHALLOW WATERS OF THE CONTINENTAL SHELVES ..................................4  1.  Internal Tides—Internal Waves Generated by Tidal Forcing

Variability in Benthic Exchange Rate, Depth, and Residence Time Beneath a Shallow Coastal Estuary

NASA Astrophysics Data System (ADS)

Russoniello, Christopher J.; Heiss, James W.; Michael, Holly A.

2018-03-01

Hydrodynamically driven benthic exchange of water between the water column and shallow seabed aquifer is a significant and dynamic component of coastal and estuarine fluid budgets. Associated exchange of solutes promotes ecologically important chemical reactions, so quantifying benthic exchange rates, depths, and residence times constrains coastal chemical cycling estimates. We present the first combined field, numerical, and analytical modeling investigation of wave-induced exchange. Temporal variability of exchange was calculated with data collected by instruments deployed in a shallow estuary for 11 days. Differential pressure sensors recorded pressure gradients across the seabed, and up- and down-looking ADCPs recorded currents and pressures to determine wave parameters, surface-water currents, and water depth. Wave-induced exchange was calculated (1) directly from differential pressure measurements, and indirectly with an analytical model based on wave parameters from (2) ADCP and (3) wind data. Wave-induced exchange from pressure measurements and ADCP-measured wave parameters matched well, but both exceeded wind-based values. Exchange induced by tidal pumping and current-bed form interaction—the other primary drivers in shallow coastal waters were calculated from tidal stage variation and ADCP-measured currents. Exchange from waves (mean = 20.0 cm/d; range = 1.75-92.3 cm/d) greatly exceeded exchange due to tides (mean = 3.7 cm/d) and current-bed form interaction (mean = 6.5 × 10-2 cm/d). Groundwater flow models showed aquifer properties affect wave-driven benthic exchange: residence time and depth increased and exchange rates decreased with increasing hydraulic diffusivity (ratio of aquifer permeability to compressibility). This new understanding of benthic exchange will help managers assess its control over chemical fluxes to marine systems.

Ocean Renewable Energy Research at U. New Hampshire

NASA Astrophysics Data System (ADS)

Wosnik, M.; Baldwin, K.; White, C.; Carter, M.; Gress, D.; Swift, R.; Tsukrov, I.; Kraft, G.; Celikkol, B.

2008-11-01

The University of New Hampshire (UNH) is strategically positioned to develop and evaluate wave and tidal energy extraction technologies, with much of the required test site infrastructure in place already. Laboratory facilities (wave/tow tanks, flumes, water tunnels) are used to test concept validation models (scale 1:25--100) and design models (scale 1:10--30). The UNH Open Ocean Aquaculture (OOA) site located 1.6 km south of the Isles of Shoals (10 km off shore) and the General Sullivan Bridge testing facility in the Great Bay Estuary are used to test process models (scale 1:3--15) and prototype/demonstration models (scale 1:1-- 4) of wave energy and tidal energy extraction devices, respectively. Both test sites are easily accessible and in close proximity of UNH, with off-the-shelf availability. The Great Bay Estuary system is one of the most energetic tidally driven estuaries on the East Coast of the U.S. The current at the General Sullivan bridge test facility reliably exceeds four knots over part of the tidal cycle. The OOA site is a ten year old, well established offshore test facility, and is continually serviced by a dedicated research vessel and operations/diving crew. In addition to an overview of the physical resources, results of recent field testing of half- and full-scale hydrokinetic turbines, and an analysis of recent acoustic Doppler surveys of the tidal estuary will be presented.

Sediment transport and development of banner banks and sandwaves in an extreme tidal system: Upper Bay of Fundy, Canada

NASA Astrophysics Data System (ADS)

Li, Michael Z.; Shaw, John; Todd, Brian J.; Kostylev, Vladimir E.; Wu, Yongsheng

2014-07-01

Multibeam sonar mapping and geophysical and geological groundtruth surveys were coupled with tidal current and sediment transport model calculations to investigate the sediment transport and formation processes of the complex seabed features off the Cape Split headland in the upper Bay of Fundy. The Cape Split banner bank, composed of coarse to very coarse sand, is a southwest-northeast oriented, large tear-drop shaped sand body with superimposed sand waves that show wavelengths from 15 to 525 m and heights from 0.5 to 19 m. Isolated and chains of barchan dunes occur on top of a shadow bank to the southeast of the banner bank. The barchan dunes are composed of well-sorted medium sand and are oriented northwest-southeast. Their mean height and width are 1.5 and 55 m, respectively. A gravel bank, with an elongated elliptical shape and west-east orientation, lies in the Minas Passage erosional trough east of the headland to form the counterpart to the sandy Cape Split banner bank. The southern face is featureless but the northern face is covered by gravel megaripples. Tidal model predictions and sediment transport calculations show that the formation of the banner bank and the gravel bank are due to the development of the transient counter-clockwise and clockwise tidal eddies respectively to the west and east of the headland. The formation of barchan dunes is controlled by the nearly unidirectional flow regime in outer Scots Bay. Sand waves on the flanks of the Cape Split banner bank show opposite asymmetry and the barchan dunes are asymmetric to the northeast. The tidal current and sediment transport predictions corroborate bedform asymmetry to show that sand wave migration and net sediment transport is to southwest on the northern flank of the banner bank but to northeast on the southern bank. Long-term migration of the Scots Bay barchan dunes is to the northeast. Spring-condition tidal currents can cause frequent mobilization and high-stage transport over the banner bank and barchan dunes. Strong currents in Minas Passage can cause infrequent low-stage transport over the megarippled northern face but are not high enough to mobilize the coarser gravels on the southern face of the gravel bank.

Improving an Assessment of Tidal Stream Energy Resource for Anchorage, Alaska

NASA Astrophysics Data System (ADS)

Xu, T.; Haas, K. A.

2016-12-01

Increasing global energy demand is driving the pursuit of new and innovative energy sources leading to the need for assessing and utilizing alternative, productive and reliable energy resources. Tidal currents, characterized by periodicity and predictability, have long been explored and studied as a potential energy source, focusing on many different locations with significant tidal ranges. However, a proper resource assessment cannot be accomplished without accurate knowledge of the spatial-temporal distribution and availability of tidal currents. Known for possessing one of the top tidal energy sources along the U.S. coastline, Cook Inlet, Alaska is the area of interest for this project. A previous regional scaled resource assessment has been completed, however, the present study is to focus the assessment on the available power specifically near Anchorage while significantly improving the accuracy of the assessment following IEC guidelines. The Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system is configured to simulate the tidal flows with grid refinement techniques for a minimum of 32 days, encompassing an entire lunar cycle. Simulation results are validated by extracting tidal constituents with harmonic analysis and comparing tidal components with National Oceanic and Atmospheric Administration (NOAA) observations and predictions. Model calibration includes adjustments to bottom friction coefficients and the usage of different tidal database. Differences between NOAA observations and COAWST simulations after applying grid refinement decrease, compared with results from a former study without grid refinement. Also, energy extraction is simulated at potential sites to study the impact on the tidal resources. This study demonstrates the enhancement of the resource assessment using grid refinement to evaluate tidal energy near Anchorage within Cook Inlet, Alaska, the productivity that energy extraction can achieve and the change in tidal currents caused by energy extraction.

Dynamic equilibrium behaviour observed on two contrasting tidal flats from daily monitoring of bed-level changes

NASA Astrophysics Data System (ADS)

Hu, Zhan; van der Wal, Daphne; Cai, Huayang; van Belzen, Jim; Bouma, Tjeerd J.

2018-06-01

Dynamic equilibrium theory (DET) has been applied to tidal flats to systematically explain intertidal morphological responses to various distributions of bed shear stress (BSS). However, it is difficult to verify this theory with field observations because of the discrepancy between the idealized conceptions of theory and the complex reality of intertidal dynamics. The core relation between intertidal morphodynamics and BSS distribution can be easily masked by noise in complex datasets, leading to conclusions of insufficient field evidence to support DET. In the current study, hydrodynamic and morphodynamic data were monitored daily for one year on two tidal flats with contrasting wave exposures. BSS distribution was obtained by validated numerical models. Tidal flat dynamic equilibrium behaviour and BSS were linked via Empirical Orthogonal Function (EOF) analysis. We show that the principal morphodynamic modes corresponded well with the respective modes of BSS found at both sites. Tide-induced BSS was the dominant force at both sites, regardless of the level of wave exposure. The overall erosional and steepening trend found at the two flats can be attributed to the prevailing action of tidal forcing and reduced sediment supply. Hence, EOF analysis confirmed that tidal flat morphodynamics are consistent with DET, providing both field and model evidence to support this theory.

Framework for Identifying Key Environmental Concerns in Marine Renewable Energy Projects- Appendices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kramer, Sharon; Previsic, Mirko; Nelson, Peter

2010-06-17

Marine wave and tidal energy technology could interact with marine resources in ways that are not well understood. As wave and tidal energy conversion projects are planned, tested, and deployed, a wide range of stakeholders will be engaged; these include developers, state and federal regulatory agencies, environmental groups, tribal governments, recreational and commercial fishermen, and local communities. Identifying stakeholders’ environmental concerns in the early stages of the industry’s development will help developers address and minimize potential environmental effects. Identifying important concerns will also assist with streamlining siting and associated permitting processes, which are considered key hurdles by the industry inmore » the U.S. today. In September 2008, RE Vision consulting, LLC was selected by the Department of Energy (DoE) to conduct a scenario-based evaluation of emerging hydrokinetic technologies. The purpose of this evaluation is to identify and characterize environmental impacts that are likely to occur, demonstrate a process for analyzing these impacts, identify the “key” environmental concerns for each scenario, identify areas of uncertainty, and describe studies that could address that uncertainty. This process is intended to provide an objective and transparent tool to assist in decision-making for siting and selection of technology for wave and tidal energy development. RE Vision worked with H. T. Harvey & Associates, to develop a framework for identifying key environmental concerns with marine renewable technology. This report describes the results of this study. This framework was applied to varying wave and tidal power conversion technologies, scales, and locations. The following wave and tidal energy scenarios were considered: 4 wave energy generation technologies 3 tidal energy generation technologies 3 sites: Humboldt coast, California (wave); Makapu’u Point, Oahu, Hawaii (wave); and the Tacoma Narrows, Washington (tidal) 3 project sizes: pilot, small commercial, and large commercial The possible combinations total 24 wave technology scenarios and 9 tidal technology scenarios. We evaluated 3 of the 33 scenarios in detail: 1. A small commercial OPT Power Buoy project off the Humboldt County, California coast 2. A small commercial Pelamis Wave Power P-2 project off Makapu’u Point, Oahu, Hawaii 3. A pilot MCT SeaGen tidal project, sited in the Tacoma Narrows, Washington. This framework document used information available from permitting documents that were written to support actual wave or tidal energy projects, but the results obtained here should not be confused with those of the permitting documents1. The main difference between this framework document and permitting documents of currently proposed pilot projects is that this framework identifies key environmental concerns and describes the next steps in addressing those concerns; permitting documents must identify effects, find or declare thresholds of significance, evaluate the effects against the thresholds, and find mitigation measures that will minimize or avoid the effects so they can be considered less-than-significant. Two methodologies, 1) an environmental effects analysis and 2) Raptools, were developed and tested to identify potential environmental effects associated with wave or tidal energy conversion projects. For the environmental effects analysis, we developed a framework based on standard risk assessment techniques. The framework was applied to the three scenarios listed above. The environmental effects analysis addressed questions such as: What is the temporal and spatial exposure of a species at a site? What are the specific potential project effects on that species? What measures could minimize, mitigate, or eliminate negative effects? Are there potential effects of the project, or species’ response to the effect, that are highly uncertain and warrant additional study? The second methodology, Raptools, is a collaborative approach useful for evaluating multiple characteristics of numerous siting or technology alternatives, and it allows us to graphically compare alternatives. We used Raptools to answer these questions: How do the scenarios compare, in terms of exposure, risks, and effects to the ecological and human environments? Are there sites that seem to present the fewest effects regardless of technology and scale? Which attributes account for many or much of the effects associated with wave or tidal energy development?« less

Geo-morphological changes of the Wanpingkou tidal system arising from the building of a sailing boat station in Rizhao of China.

PubMed

Bian, Shuhua; Zhang, Yuanzhi; Feng, Aiping; Chiu, Long; Wu, Sangyun; Hu, Zejian

2008-03-01

This paper examines a small tidal system in Wanpingkou, Rizhao of China. The tidal system was originally maintained by a balance of the natural interaction between tidal currents and waves. But this tidal system was diminishing by reclamation processes since the 1980s, especially in 2003 when a sailing boat station was built in the study area. To investigate the stability and development mechanism of the tidal system, its feasibility was evaluated before the sailing boat station was built. The erosion and deposition in and out of the tidal system was analyzed, forecasted and compared with the data from field monitoring. The results show that the tidal system would remain relatively stable, although its adjacent shoreline might change somewhat after the newly built sailing boat station. This change would also affect the coastal water and wetland environment in the study area. Further field monitoring in the area is still necessary.

The Impact of Hydrodynamics in Erosion - Deposition Process in Can Gio Mangrove Biosphere Reserve, South Viet Nam

NASA Astrophysics Data System (ADS)

Vo-Luong, H. P.

2014-12-01

Can Gio Mangrove Biosphere Reserve is always considered as a friendly green belt to protect and bring up the habitants. However, recently some mangrove areas in the Dong Tranh estuary are being eroded seriously. Based on the field measurements in SW and NE monsoons as well as data of topography changes in 10 years, it is proved that hydrodynamics of waves, tidal currents and riverine currents are the main reasons for erosion-deposition processes at the studied site. The erosion-deposition process changes due to monsoon. The analysed results show that high waves and tidal oscillation cause the increase of the erosion rate in NE monsoon. However, high sediment deposition occurs in SW monsoon due to weak waves and more alluvium from upstream. Many young mangrove trees grow up and develop in the SW monsoon. From the research, it is strongly emphasized the role of mangrove forests in soil retention and energy dissipation.

Coastal circulation and potential coral-larval dispersal in Maunalua Bay, O'ahu, Hawaii—Measurements of waves, currents, temperature, and salinity, June-September 2010

USGS Publications Warehouse

Presto, M. Katherine; Storlazzi, Curt D.; Logan, Joshua B.; Reiss, Thomas E.; Rosenberger, Kurt J.

2012-01-01

This report presents a summary of fieldwork conducted in Maunalua Bay, O'ahu, Hawaii to address coral-larval dispersal and recruitment from June through September, 2010. The objectives of this study were to understand the temporal and spatial variations in currents, waves, tides, temperature, and salinity in Maunalua Bay during the summer coral-spawning season of Montipora capitata. Short-term vessel surveys and satellite-tracked drifters were deployed to measure currents during the June 2010 spawning event and to supplement the longer-term measurements of currents and water-column properties by fixed, bottom-mounted instruments deployed in Maunalua Bay. These data show that currents at the surface and just below the surface where coral larvae are found are often oriented in opposite directions due primarily to tidal and trade-winds forcing as the primary mechanisms of circulation in the bay. These data extend our understanding of coral-larvae dispersal patterns due to tidal and wind-driven currents and may be applicable to larvae of other Hawaiian corals.

Fluid dynamics of liquids on Titans surface

NASA Astrophysics Data System (ADS)

Ori, Gian Gabriele; Marinangeli, Lucia; Baliva, Antonio; Bressan, Mario; Strom, Robert G.

1998-10-01

On the surface of Titan liquids can be present in three types of environments : (i) oceans, (ii) seas and lakes, and (iii) fluvial channels. The liquid in these environments will be affected by several types of motion: progressive (tidal) waves, wind-generated waves and unidirectional currents. The physical parameters of the liquid on Titans surface can be reconstructed using the Peng-Robinson equation of state. The total energy of the waves, both tidal and wind, depends on the gravity and liquid density ; both values are lower on Titan than on Earth. Thus, the same total energy will produce larger waves on Titan. This is also valid also for the progressive waves, as it is confirmed by the physical relationship between horizontal velocity, wave amplitude, and depth of the liquid. Wind-driven waves also will tend to be larger, because the viscosity of the liquid (which is lower on Titan) controls the deformation of the liquid under shear stress. Wind-generated waves would be rather large, but the dimension of the liquid basin limits the size of the waves ; in small lakes or seas the wave power cannot reach large values. Unidirectional currents are also affected by the liquid properties. Both the relations from driving and resting forces and the Reynolds number suggests that the flows exhibit a large erosional capacity and that, theoretically, a true fluvial network could be formed. However, caution should be exercised, because the cohesion of the sedimentary interface can armour bottom and induce laterally extensive, unchanelled sheet flows with small erosional capacity.

Distinguishing boson stars from black holes and neutron stars from tidal interactions in inspiraling binary systems

NASA Astrophysics Data System (ADS)

Sennett, Noah; Hinderer, Tanja; Steinhoff, Jan; Buonanno, Alessandra; Ossokine, Serguei

2017-07-01

Binary systems containing boson stars—self-gravitating configurations of a complex scalar field—can potentially mimic black holes or neutron stars as gravitational-wave sources. We investigate the extent to which tidal effects in the gravitational-wave signal can be used to discriminate between these standard sources and boson stars. We consider spherically symmetric boson stars within two classes of scalar self-interactions: an effective-field-theoretically motivated quartic potential and a solitonic potential constructed to produce very compact stars. We compute the tidal deformability parameter characterizing the dominant tidal imprint in the gravitational-wave signals for a large span of the parameter space of each boson star model, covering the entire space in the quartic case, and an extensive portion of interest in the solitonic case. We find that the tidal deformability for boson stars with a quartic self-interaction is bounded below by Λmin≈280 and for those with a solitonic interaction by Λmin≈1.3 . We summarize our results as ready-to-use fits for practical applications. Employing a Fisher matrix analysis, we estimate the precision with which Advanced LIGO and third-generation detectors can measure these tidal parameters using the inspiral portion of the signal. We discuss a novel strategy to improve the distinguishability between black holes/neutrons stars and boson stars by combining tidal deformability measurements of each compact object in a binary system, thereby eliminating the scaling ambiguities in each boson star model. Our analysis shows that current-generation detectors can potentially distinguish boson stars with quartic potentials from black holes, as well as from neutron-star binaries if they have either a large total mass or a large (asymmetric) mass ratio. Discriminating solitonic boson stars from black holes using only tidal effects during the inspiral will be difficult with Advanced LIGO, but third-generation detectors should be able to distinguish between binary black holes and these binary boson stars.

Evaluation of sediment transport at a fetch-limited beach from spring to neap tide

NASA Astrophysics Data System (ADS)

Carrasco, Ana Rita; Ferreira, Óscar; Matias, Ana; Freire, Paula; Alveirinho Dias, João.

2010-05-01

Sediment transport studies are useful tools for the determination of sediment budgets, important in the definition of management policies, in particular in environments not fully understood like fetch-limited beaches. Only a few studies have been made with respect to these beaches, and research efforts need to be continued to correctly quantify the main factors governing morphological changes. The present study provides new insights on sediment transport at a fetch-limited backbarrier beach located at the Peninsula do Ancão (Ria Formosa, South of Portugal). The field site extends over ~150 m and includes a sandy beach with a low and narrow reflective morphology, and an external sand bank at the seaward edge of the sub-aerial beach profile. Fluorescent tracers were used to measure the short-term sediment transport (rates and directions) from spring to neap tides, for fair-weather conditions. The experiment was set at two beach morphologies: beach face and sand bank. Tracer was released on 20th March 2008 at both sites, and sampling was conducted at low tide, each 24h, during 7 days. In situ fluorescent tracer detection was performed with UV light. Currents were obtained with a portable single-axis electromagnetic current meter located at the beach face, and an Aquadopp Profiler located at the sand bank. Local waves were obtained by numerical modelling for the study area, based on prevailing winds (measured by a nearby meteorological station), and using available bathymetric surveys. Tracer trends, tidal currents, wind conditions and waves were integrative in order to determine to which forcing mechanism the beach morphology was more responsive. Daily wind intensities were, in average, close to 5 m/s, and maximum estimated significant wave height (Hs) did not exceed 0.045 m. Daily mean wave period ranged from 0.5 s to 0.7 s. The maximum tidal range was 2.8 m. Currents were of higher magnitude at the sand bank than at the beach face, with the maximum during ebb tide (0.50 m/s). At the beach face, maximum velocities are very similar for both ebb and flood tide, with a maximum of 0.26 m/s. Tracer displacement was greater at the beach face, indicating that this is the most active part of the profile during the experiment. At the sand bank, tracer dispersion was greater, but tracer advection was shorter. Tracer isopachs illustrate a relatively independency of both analysed morphologies, without significant exchange across the profile. At both morphologies, the residual transport is dominated by the longshore component, and mostly directed towards the ebb. Ebb directed transport agrees with ebb dominance on tidal currents at this location. Results suggest a tidal and current dominance. Tidal range assumes particular importance at beach face.

Gravitational waveforms for neutron star binaries from binary black hole simulations

NASA Astrophysics Data System (ADS)

Barkett, Kevin; Scheel, Mark; Haas, Roland; Ott, Christian; Bernuzzi, Sebastiano; Brown, Duncan; Szilagyi, Bela; Kaplan, Jeffrey; Lippuner, Jonas; Muhlberger, Curran; Foucart, Francois; Duez, Matthew

2016-03-01

Gravitational waves from binary neutron star (BNS) and black-hole/neutron star (BHNS) inspirals are primary sources for detection by the Advanced Laser Interferometer Gravitational-Wave Observatory. The tidal forces acting on the neutron stars induce changes in the phase evolution of the gravitational waveform, and these changes can be used to constrain the nuclear equation of state. Current methods of generating BNS and BHNS waveforms rely on either computationally challenging full 3D hydrodynamical simulations or approximate analytic solutions. We introduce a new method for computing inspiral waveforms for BNS/BHNS systems by adding the post-Newtonian (PN) tidal effects to full numerical simulations of binary black holes (BBHs), effectively replacing the non-tidal terms in the PN expansion with BBH results. Comparing a waveform generated with this method against a full hydrodynamical simulation of a BNS inspiral yields a phase difference of < 1 radian over ~ 15 orbits. The numerical phase accuracy required of BNS simulations to measure the accuracy of the method we present here is estimated as a function of the tidal deformability parameter λ.

Morphodynamics of a tidal ridge system in the southwestern Yellow Sea: HF radar study

NASA Astrophysics Data System (ADS)

Zhong, Yao-Zhao; Li, Yan; Wu, Xiong-Bin; Gao, Shu; Zhou, Tao; Wang, Ya Ping; Gao, Jian-Hua

2018-06-01

A radial tidal ridge system is present throughout the coastal waters of the southwestern Yellow Sea (China) with varied and complicated ridges and channels between them. A newly designed ground-wave high-frequency (HF radar), with full-coverage and high spatial-temporal resolution, was employed in this study to measure the surface currents and bathymetric features correlated wave celerity in the study area from July 17 to August 6, 2011. We found that the spatial distribution pattern of the tidal channels is generally stable with periodic adjustments during a spring-neap tidal cycle and with higher degree of spatial orderliness from neap to spring tides than from spring to neap tides; the nearshore part of the channels is most stable in lateral, the middle part is relatively lateral unstable, and the offshore part changes complicatedly; flood-dominated channels and ebb-dominated ridges are identified using HF radar signals. The horizontal Kelvin number (Keh) is workable in lateral stability evaluation. This study reveals the potential of HF radar in morphodynamic studies on shallow coastal waters.

Water level effects on breaking wave setup for Pacific Island fringing reefs

NASA Astrophysics Data System (ADS)

Becker, J. M.; Merrifield, M. A.; Ford, M.

2014-02-01

The effects of water level variations on breaking wave setup over fringing reefs are assessed using field measurements obtained at three study sites in the Republic of the Marshall Islands and the Mariana Islands in the western tropical Pacific Ocean. At each site, reef flat setup varies over the tidal range with weaker setup at high tide and stronger setup at low tide for a given incident wave height. The observed water level dependence is interpreted in the context of radiation stress gradients specified by an idealized point break model generalized for nonnormally incident waves. The tidally varying setup is due in part to depth-limited wave heights on the reef flat, as anticipated from previous reef studies, but also to tidally dependent breaking on the reef face. The tidal dependence of the breaking is interpreted in the context of the point break model in terms of a tidally varying wave height to water depth ratio at breaking. Implications for predictions of wave-driven setup at reef-fringed island shorelines are discussed.

Preliminary hydrodynamic analysis of landslide-generated waves in Tidal Inlet, Glacier Bay National Park, Alaska

USGS Publications Warehouse

Geist, Eric L.; Jakob, Matthias; Wieczoreck, Gerald F.; Dartnell, Peter

2003-01-01

A landslide block perched on the northern wall of Tidal Inlet, Glacier Bay National Park (Figure 1), has the potential to generate large waves in Tidal Inlet and the western arm of Glacier Bay if it were to fail catastrophically. Landslide-generated waves are a particular concern for cruise ships transiting through Glacier Bay on a daily basis during the summer months. The objective of this study is to estimate the range of wave amplitudes and periods in the western arm of Glacier Bay from a catastrophic landslide in Tidal Inlet. This study draws upon preliminary findings of a field survey by Wieczorek et al. (2003), and evaluates the effects of variations in landslide source parameters on the wave characteristics.

Tidal and residual currents across the northern Ryukyu Island chain observed by ferryboat ADCP

NASA Astrophysics Data System (ADS)

Liu, Zhao-Jun; Nakamura, Hirohiko; Zhu, Xiao-Hua; Nishina, Ayako; Dong, Menghong

2017-09-01

Ferryboat Acoustic Doppler Current Profiler (ADCP) data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern Ryukyu Island chain (RIC) between the islands of Okinawa and Amamioshima. In this region, the M2 tide current is the strongest tidal component, and the K1 tide current is the strongest diurnal tidal component. The corresponding maximum amplitudes are 40 and 34 cm s-1, respectively. After removal of the tidal currents, the mean volume transport, 1.5 ± 2.7 Sv, flows into the East China Sea (ECS) from the western North Pacific through four channels in this area. In an empirical orthogonal function (EOF) analysis performed to clarify the temporal and spatial variability of currents through the four channels, the first two EOF modes account for 71% and 18% of the total variance, respectively. The EOF1 mode shows a clear bottom-intensified mode through the deep channel, which is likely to be formed by the propagation of bottom-trapped long topographic Rossby wave caused by the impingement of westward-propagating mesoscale eddies upon the eastern slope of the northern RIC. The EOF2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the Kuroshio flow region around the northern RIC in October-November. This study provides observational evidence of the water exchanges across the northern RIC, which is essential for constructing a circulation scheme in the North Pacific subtropical western boundary region.

Model Predictive Control-based Power take-off Control of an Oscillating Water Column Wave Energy Conversion System

NASA Astrophysics Data System (ADS)

Rajapakse, G.; Jayasinghe, S. G.; Fleming, A.; Shahnia, F.

2017-07-01

Australia’s extended coastline asserts abundance of wave and tidal power. The predictability of these energy sources and their proximity to cities and towns make them more desirable. Several tidal current turbine and ocean wave energy conversion projects have already been planned in the coastline of southern Australia. Some of these projects use air turbine technology with air driven turbines to harvest the energy from an oscillating water column. This study focuses on the power take-off control of a single stage unidirectional oscillating water column air turbine generator system, and proposes a model predictive control-based speed controller for the generator-turbine assembly. The proposed method is verified with simulation results that show the efficacy of the controller in extracting power from the turbine while maintaining the speed at the desired level.

Tidal Conversion and Mixing Poleward of the Critical Latitude (an Arctic Case Study)

NASA Astrophysics Data System (ADS)

Rippeth, Tom P.; Vlasenko, Vasiliy; Stashchuk, Nataliya; Scannell, Brian D.; Green, J. A. Mattias; Lincoln, Ben J.; Bacon, Sheldon

2017-12-01

The tides are a major source of the kinetic energy supporting turbulent mixing in the global oceans. The prime mechanism for the transfer of tidal energy to turbulent mixing results from the interaction between topography and stratified tidal flow, leading to the generation of freely propagating internal waves at the period of the forcing tide. However, poleward of the critical latitude (where the period of the principal tidal constituent exceeds the local inertial period), the action of the Coriolis force precludes the development of freely propagating linear internal tides. Here we focus on a region of sloping topography, poleward of the critical latitude, where there is significant conversion of tidal energy and the flow is supercritical (Froude number, Fr > 1). A high-resolution nonlinear modeling study demonstrates the key role of tidally generated lee waves and supercritical flow in the transfer of energy from the barotropic tide to internal waves in these high-latitude regions. Time series of flow and water column structure from the region of interest show internal waves with characteristics consistent with those predicted by the model, and concurrent microstructure dissipation measurements show significant levels of mixing associated with these internal waves. The results suggest that tidally generated lee waves are a key mechanism for the transfer of energy from the tide to turbulence poleward of the critical latitude.

Secondary Flows and Sediment Transport due to Wave - Current Interaction

NASA Astrophysics Data System (ADS)

Ismail, Nabil; Wiegel, Robert

2015-04-01

Objectives: The main purpose of this study is to determine the modifications of coastal processes driven by wave-current interaction and thus to confirm hydrodynamic mechanisms associated with the interaction at river mouths and tidal inlets where anthropogenic impacts were introduced. Further, the aim of the work has been to characterize the effect of the relative strength of momentum action of waves to the opposing current on the nearshore circulation where river flow was previously effective to entrain sediments along the shoreline. Such analytical information are useful to provide guidelines for sustainable design of coastal defense structures. Methodology and Analysis: Use is made of an earlier study reported by the authors (1983) on the interaction of horizontal momentum jets and opposing shallow water waves at shorelines, and of an unpublished laboratory study (1980). The turbulent horizontal discharge was shore-normal, directed offshore, and the incident wave direction was shore-normal, travelling toward shore. Flow visualization at the smooth bottom and the water surface, velocity and water surface elevation measurements were made. Results were obtained for wave , current modifications as well as the flow pattern in the jet and the induced circulation on both sides of the jet, for a range of wave and jet characteristics. The experimental data, obtained from measurement in the 3-D laboratory basin, showed several distinct flow pattern regimes on the bottom and the water surface. The observed flow circulation regimes were found to depend on the ratio of the wave momentum action on the jet to the jet initial momentum. Based on the time and length scales of wave and current parameters and using the time average of the depth integrated conservation equations, it is found that the relative strength of the wave action on the jet could be represented by a dimensionless expression; Rsm ( ) 12ρSa20g-L0h-Cg- 2 Rsm ≈ (C0 - U) /ρ0U w (1) In the above dimensionless expression, ρs is the seawater mass density, ρ is the river current mass density, a0 is the deep water wave amplitude, g is the acceleration of gravity, Cg is the wave group velocity, L is the deep water wave length, h is the average water depth near the river mouth, C0 is the deep water wave phase velocity, U is the average jet exit velocity and w is the river or the tidal inlet effective width. The values of the above number were found to be in the range between 1.0 and 6.0-8.0 for the examined laboratory and field case studies for non-buoyant jets. Upper bound corresponds to cases of higher wave activity on the coast while the lower bound corresponds to cases of tidal currents with minimum wave activity, Coastal Processes Modifications due to River and Ebb Current Interaction with Opposing Waves: Confirmation of the obtained theoretical expression was obtained by comparison against field data for shoreline variability at river mouths and the formation of accretion shoals and erosion spots at tidal inlets and ocean outfalls in the USA and the Nile delta coastline. The predicted extent of the coast reshaping process, due to shoreline erosion and subsequent accretion, due to the absence of the river Nile current after 1965, east of the Rosetta headland, was determined. The obtained shoreline erosion spatial extent using the above correlation showed that the long term length of coastline recession would be in the neighborhood of 16-20 km east of Rosetta headland (1990-2014). Such results were further confirmed by the recent satellite data (Ghoneim, et al, 2015). The results of the present work were well compared to the data on Fort Pierce Inlet, Florida, where severe erosion is known to exist on both sides of the inlet (Joshi, 1983). The current results are qualitatively in parallel to that obtained recently by the numerical model Delft3D coupled with the wave model SWAN ( Nardin, et al, 2013) on wave- current interaction at river mouths and the formation of mouth bars. Further analyses were also conducted to test the validity of the derived expression to the cases of wave interaction with buoyant currents in shallow waters. The buoyant jets represent the thermal discharges from power plants on coastlines of Diablo Canyon cove in CA at the Pacific Ocean (Ismail, et al,1988) and at the northern coast of Egypt at Al-Arish. The comparison showed higher values range of Rsm for the cases of buoyant jets. References: Ghoneim, E., Mashaly , J., Gamble, D., Halls, J., and AbuBakr, M. (2015). "Nile Delta Exhibited a Spatial Reversal in the Rates of Shoreline Retreat on the Rosetta Promontory; comparing pre- and post-beach protection", Geomorphology, 228,1-14. Ismail, N. (2007). "Reynolds Stresses and Velocity Distributions in a Wave-Current Coexisting Environment', Discussion, J. Waterway, Port, Coastal, and Ocean Engineering,10.1061/(ASCE)0733-950X(2007)133:2(168),168-170. Ismail, N.M., Wiegel, R.L., Ryan, P.J., and Tu, S. W. (1988). "Mixing of Thermal Discharges in Coastal Waters" , 21 st International Conference on Coastal Engineering, ASCE, Malaga, Spain, 2521-2535. Ismail, N. (1984). "Wave-Current Models for Design of Marine Structures" , Journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 110, No. 4, 432-447. Ismail, N.M. and Wiegel, R.L. (1983). "Opposing Waves Effect on Momentum Jets Spreading Rate", J. Waterways, Port, Coastal and Ocean Division, Proc., ASCE, vol. 109, No.4, 465-483. Joshi, P. and Taylor, R. (1983). 'Circulation Induced by Tidal Jets.' J. Waterway, Port, Coastal, Ocean Eng., 109(4), 445-464. Nardin, W., Mariotti, G., Edmonds, D., Guercio, R., and Fagherazzi, S. (2013). "Growth of River Mouth Bars in Sheltered Bays in the Presence of Frontal Waves." Journal of Geophysical Research: Earth Surface,10, 872-886.

On the effects of tidal interaction on thin accretion disks: An analytic study

NASA Technical Reports Server (NTRS)

Dgani, R.; Livio, M.; Regev, O.

1994-01-01

We calculate tidal effects on two-dimensional thin accretion disks in binary systems. We apply a perturbation expansion to obtain an analytic solution of the tidally induced waves. We obtain spiral waves that are stronger at the inner parts of the disks, in addition to a local disturbance which scales like the strength of the local tidal force. Our results agree with recent calculations of the linear response of the disk to tidal interaction.

Towards a better understanding of tidal dissipation at corotation layers in differentially rotating stars and planets

NASA Astrophysics Data System (ADS)

Astoul, A.; Mathis, S.; Baruteau, C.; André, Q.

2017-12-01

Star-planet tidal interactions play a significant role in the dynamical evolution of close-in planetary systems. We investigate the propagation and dissipation of tidal inertial waves in a stellar/planetary convective region. We take into account a latitudinal differential rotation for the background flow, similar to what is observed in the envelope of low-mass stars like the Sun. Previous works have shown that differential rotation significantly alters the propagation and dissipation properties of inertial waves. In particular, when the Doppler-shifted tidal frequency vanishes in the fluid, a critical layer forms where tidal dissipation can be greatly enhanced. Our present work develops a local analytic model to better understand the propagation and dissipation properties of tidally forced inertial waves at critical layers.

The mid-Holocene to present large-scale morphodynamic and coupled fluvial-tidal sedimentologic evolution of the Lower Columbia River, WA/OR, USA

NASA Astrophysics Data System (ADS)

Prokocki, E.; Best, J.; Ashworth, P. J.; Parsons, D. R.; Sambrook Smith, G.; Nicholas, A. P.; Simpson, C.; Wang, H.; Sandbach, S.; Keevil, C.

2015-12-01

Optically stimulated luminescence (OSL) dating of four deep sediment cores (≤ 20m depth), in conjunction with shallow vibracores (≤ 6m depth), obtained from mid-channel bars in the lower Columbia River (LCR), USA, provides new insights into the mid-Holocene to present geomorphic and coupled sedimentological evolution of the LCR fluvial-tidal zone. These data reveal that the relatively coarse-grained basal sediments of mid-channel bars positioned across the LCR tidal-fluvial hydraulic regime were deposited at c. 2.5 to 2.0 ka, and not at c. 8.0 ka as previously reported. Thus, these younger depositional ages of basal sediments relative to previous studies coupled with the overall sedimentary architecture of these bars, and the absence of a temporal lag in the timing of basal sedimentation between bars located from river kilometer 51.1 to 29.3, challenges existing models that these bars represent: (a) estuarine tidal-bars, or (b) bay-head deltaic deposits. Within the context of post glacial Holocene sea-level rise, our results suggest these bars represent vertical construction of a LCR fluvial top-set from c. 2.5- 2.0 ka to the present, as the regional rate of sea-level rise slowed to ≤ 1.4 mmyr-1. Within this geomorphic context, two tidal-fluvial sedimentological signatures can be identified: (i) in the downstream direction, basal bar deposits incorporate a larger percentage of finer-grained interbeds, and (ii) vertically stacked silt/very-fine sand draped current ripple cross-laminae become prevalent from approximately 5 m in depth to the bar surfaces. The preservation of finer-grained interbeds within basal bar deposits is reasoned to be caused by the flocculation and settling of suspended sediment enhanced by the turbidity maximum. The stacked draped current ripple cross-laminae are interpreted to result from tidal-currents generating asymmetric current ripples that were draped by fine-sediment entrained by wind-waves, which fell-out of suspension during reduced wave activity, slackwater intervals, and periods when the turbidity maximum was active.

40 CFR 230.60 - General evaluation of dredged or fill material.

Code of Federal Regulations, 2014 CFR

2014-07-01

... generally found in areas of high current or wave energy such as streams with large bed loads or coastal... show watercourses, surface relief, proximity to tidal movement, private and public roads, location of...

40 CFR 230.60 - General evaluation of dredged or fill material.

Code of Federal Regulations, 2013 CFR

2013-07-01

... generally found in areas of high current or wave energy such as streams with large bed loads or coastal... show watercourses, surface relief, proximity to tidal movement, private and public roads, location of...

40 CFR 230.60 - General evaluation of dredged or fill material.

Code of Federal Regulations, 2012 CFR

2012-07-01

... generally found in areas of high current or wave energy such as streams with large bed loads or coastal... show watercourses, surface relief, proximity to tidal movement, private and public roads, location of...

40 CFR 230.60 - General evaluation of dredged or fill material.

Code of Federal Regulations, 2010 CFR

2010-07-01

... generally found in areas of high current or wave energy such as streams with large bed loads or coastal... show watercourses, surface relief, proximity to tidal movement, private and public roads, location of...

40 CFR 230.60 - General evaluation of dredged or fill material.

Code of Federal Regulations, 2011 CFR

2011-07-01

... generally found in areas of high current or wave energy such as streams with large bed loads or coastal... show watercourses, surface relief, proximity to tidal movement, private and public roads, location of...

Recent scientific advances and their implications for sand management near San Francisco, California: the influences of the ebb tidal delta

USGS Publications Warehouse

Hanes, Daniel M.; Barnard, Patrick L.; Dallas, Kate; Elias, Edwin; Erikson, Li H.; Eshleman, Jodi; Hansen, Jeff; Hsu, Tian Jian; Shi, Fengyan

2011-01-01

Recent research in the San Francisco, California, U.S.A., coastal region has identified the importance of the ebb tidal delta to coastal processes. A process-based numerical model is found to qualitatively reproduce the equilibrium size and shape of the delta. The ebb tidal delta itself has been contracting over the past century, and the numerical model is applied to investigate the sensitivity of the delta to changes in forcing conditions. The large ebb tidal delta has a strong influence upon regional coastal processes. The prominent bathymetry of the ebb tidal delta protects some of the coast from extreme storm waves, but the delta also focuses wave energy toward the central and southern portions of Ocean Beach. Wave focusing likely contributes to a chronic erosion problem at the southern end of Ocean Beach. The ebb tidal delta in combination with non-linear waves provides a potential cross-shore sediment transport pathway that probably supplies sediment to Ocean Beach.

Variability in benthic exchange rate, depth, and residence time beneath a shallow coastal estuary

NASA Astrophysics Data System (ADS)

Russoniello, C. J.; Michael, H. A.; Heiss, J.

2017-12-01

Hydrodynamically-driven exchange of water between the water column and shallow seabed aquifer, benthic exchange, is a significant and dynamic component of coastal and estuarine fluid budgets, but wave-induced benthic exchange has not been measured in the field. Mixing between surface water and groundwater solutes promotes ecologically important chemical reactions, so quantifying benthic exchange rates, depths, and residence times, constrains estimates of coastal chemical cycling. In this study, we present the first field-based direct measurements of wave-induced exchange and compare it to exchange induced by the other primary drivers of exchange - tides, and currents. We deployed instruments in a shallow estuary to measure benthic exchange and temporal variability over an 11-day period. Differential pressure sensors recorded pressure gradients across the seabed, and up-and down-looking ADCPs recorded currents and pressures from which wave parameters, surface-water currents, and water depth were determined. Wave-induced exchange was calculated directly from 1) differential pressure measurements, and indirectly with an analytical solution based on wave parameters from 2) ADCP and 3) weather station data. Groundwater flow models were used to assess the effects of aquifer properties on benthic exchange depth and residence time. Benthic exchange driven by tidal pumping or current-bedform interaction was calculated from tidal stage variation and from ADCP-measured currents at the bed, respectively. Waves were the primary benthic exchange driver (average = 20.0 cm/d, maximum = 92.3 cm/d) during the measurement period. Benthic exchange due to tides (average = 3.7 cm/d) and current-bedform interaction (average = 6.5x10-2 cm/d) was much lower. Wave-induced exchange calculated from pressure measurements and ADCP-measured wave parameters matched well, but wind-based rates underestimated wave energy and exchange. Groundwater models showed that residence time and depth increased in high-permeability, incompressible aquifers, and exchange rates increased in low-permeability, compressible aquifers. These findings support and extend the utility of existing wave-induced exchange solutions and will help managers assess the importance of benthic exchange on coastal chemical cycling.

Constraints on interquark interaction parameters with GW170817 in a binary strange star scenario

NASA Astrophysics Data System (ADS)

Zhou, En-Ping; Zhou, Xia; Li, Ang

2018-04-01

The LIGO/VIRGO detection of the gravitational waves from a binary merger system, GW170817, has put a clean and strong constraint on the tidal deformability of the merging objects. From this constraint, deep insights can be obtained in compact star equation of states, which has been one of the most puzzling problems for nuclear physicists and astrophysicists. Employing one of the most widely used quark star EOS models, we characterize the star properties by the strange quark mass (ms ), an effective bag constant (Beff), the perturbative QCD correction (a4), as well as the gap parameter (Δ ) when considering quark pairing, and investigate the dependences of the tidal deformablity on them. We find that the tidal deformability is dominated by Beff and insensitive to ms, a4. We discuss the correlation between the tidal deformability and the maximum mass (MTOV) of a static quark star, which allows the model possibility to rule out the existence of quark stars with future gravitational wave observations and mass measurements. The current tidal deformability measurement implies MTOV≤2.18 M⊙ (2.32 M⊙ when pairing is considered) for quark stars. Combining with two-solar-mass pulsar observations, we also make constraints on the poorly known gap parameter Δ for color-flavor-locked quark matter.

Effects of Stream Turbine Array Configuration on Current Energy Extraction Near an Island

NASA Astrophysics Data System (ADS)

Chen, Y.; Lin, B.; Lin, J.

2014-12-01

Enhanced tidal currents close to an island appear to present the potential for power extraction. In this research, a three-dimensional numerical model is employed to predict the tidal current energy extraction potential from turbine arrays near an island. One of the significant challenges is to determine an optimal configuration of turbine array. This paper presents a detailed work to investigate the combined influences of topographic features and array configuration on the performance of power generation. Three single row arrays and three multiple-row arrays, with turbines being arranged in a staggered manner, are examined. It has been found that a single row array with a relatively small spacing between two turbines could achieve good efficiency due to the blockage effects, whereas a larger lateral spacing gives a better performance for multi-row arrays. The reason is that the bypass flow in a staggered layout would results in shadowing effect on downstream turbines. Model results also show that the wake influence can be minimized by increasing not only the longitudinal spacing, but also the lateral spacing. The tidal current flows are shown to have been affected by the inclusion of turbines, with less fluctuant wave in a tidal cycle. The extents of the observed impacts are not only within the turbine array field, but also moving around the island and propagating to the far-field. This study can be used to provide the reference information of the commercial-scale farms for tidal energy development. Keywords: Tidal currents; Array configuration; Energy extraction; Hydrodynamic process

Patterns and drivers of daily bed-level dynamics on two tidal flats with contrasting wave exposure.

PubMed

Hu, Zhan; Yao, Peng; van der Wal, Daphne; Bouma, Tjeerd J

2017-08-02

Short-term bed-level dynamics has been identified as one of the main factors affecting biota establishment or retreat on tidal flats. However, due to a lack of proper instruments and intensive labour involved, the pattern and drivers of daily bed-level dynamics are largely unexplored in a spatiotemporal context. In this study, 12 newly-developed automatic bed-level sensors were deployed for nearly 15 months on two tidal flats with contrasting wave exposure, proving an unique dataset of daily bed-level changes and hydrodynamic forcing. By analysing the data, we show that (1) a general steepening trend exists on both tidal flats, even with contrasting wave exposure and different bed sediment grain size; (2) daily morphodynamics level increases towards the sea; (3) tidal forcing sets the general morphological evolution pattern at both sites; (4) wave forcing induces short-term bed-level fluctuations at the wave-exposed site, but similar effect is not seen at the sheltered site with smaller waves; (5) storms provoke aggravated erosion, but the impact is conditioned by tidal levels. This study provides insights in the pattern and drivers of daily intertidal bed-level dynamics, thereby setting a template for future high-resolution field monitoring programmes and inviting in-depth morphodynamic modelling for improved understanding and predictive capability.

Estimates of the Attenuation Rates of Baroclinic Tidal Energy Caused by Resonant Interactions Among Internal Waves based on the Weak Turbulence Theory

NASA Astrophysics Data System (ADS)

Onuki, Y.; Hibiya, T.

2016-02-01

The baroclinic tides are thought to be the dominant energy source for turbulent mixing in the ocean interior. In contrast to the geography of the energy conversion rates from the barotropic to baroclinic tides, which has been clarified in recent numerical studies, the global distribution of the energy sink for the resulting low-mode baroclinic tides remains obscure. A key to resolve this issue is the resonant wave-wave interactions, which transfer part of the baroclinic tidal energy to the background internal wave field enhancing the local energy dissipation rates. Recent field observations and numerical studies have pointed out that parametric subharmonic instability (PSI), one of the resonant interactions, causes significant energy sink of baroclinic tidal energy at mid-latitudes. The purpose of this study is to analyze the quantitative aspect of PSI to demonstrate the global distribution of the intensity of resonant wave interactions, namely, the attenuation rate of low-mode baroclinic tidal energy. Our approach is basically following the weak turbulence theory, which is the standard theory for resonant wave-wave interactions, where techniques of singular perturbation and statistical physics are employed. This study is, however, different from the classical theory in some points; we have reformulated the weak turbulence theory to be applicable to low-mode internal waves and also developed its numerical calculation method so that the effects of stratification profile and oceanic total depth can be taken into account. We have calculated the attenuation rate of low-mode baroclinic tidal waves interacting with the background Garrett-Munk internal wave field. The calculated results clearly show the rapid attenuation of baroclinic tidal energy at mid-latitudes, in agreement with the results from field observations and also show the zonal inhomogeneity of the attenuation rate caused by the density structures associated with the subtropical gyre. This study is expected to contribute to clarify the global distribution of the dissipation rates of baroclinic tidal energy.

Beach Erosion and Accretion: Comparison of the Seasonal Influence of Suspended- and Bedload-Sediment Transport at Grays Harbor, Washington, U. S. A.

NASA Astrophysics Data System (ADS)

Sherwood, C. R.; Lacy, J. R.; Ruggiero, P.; Kerr, L. A.; Gelfenbaum, G.; Wilson, D. J.

2001-12-01

We conducted field studies on the ebb-tidal delta near the entrance to Grays Harbor, Washington in Autumn, 1999 and Spring 2001, with the objectives of 1) providing directional wave data to validate a shoaling and refraction model for the ebb-tidal delta, and 2) measuring forcing (wave- and current-induced near-bottom velocities, accelerations, and shear stresses) and responses (bedforms, suspended-sediment profiles, and sediment fluxes) associated with intervals of beach erosion and accretion. In the Autumn experiment (October - December), tripods were deployed at shallow ( ~14-m) and deep ( ~24-m) sites on the northern, middle, and southern flanks of the ebb tidal. In the Spring experiment (May - mid-July), tripods were redeployed at four sites and a new inshore site ( ~9-m depth), and pressures, current velocities, and suspended-sediment concentrations were measured with 5-MHz acoustic Doppler velocimeters (ADVs), optical backscatterance sensors, upward-looking acoustic Doppler current profilers (ADCPs), a downward-looking pulse-coherent acoustic Doppler profiler (PCADP), and an acoustic backscatterance sensor (ABS). We also measured bedforms with profiling and imaging sonars and estimated Reynolds stresses with a pair of 10-MHz ADVs at the inshore site. Incident waves, nearshore circulation patterns, statistics of near-bottom wave- and current-induced velocities, and sediment fluxes were distinctly different in the two experiments. During the Autumn measurements, the general direction of wave approach shifted from WNW to WSW as the North Pacific weather pattern shifted from summer to winter, and we observed a large storm (offshore significant wave heights Hs of ~8 m) and a sequence of about 8 smaller events with ~4 to 5-m waves. Sediment transport was dominated by storm-induced, downwelling-favorable circulation that transported suspended sediments northward and offshore. Inferred bedload fluxes were directed shoreward, but were much smaller. In contrast, Spring wave conditions were much milder (maximum Hs of ~4 m), and waves approached mostly from the WNW. There were long periods of upwelling-favorable circulation interrupted by intervals of storm-induced northward flow. Net suspended-sediment transport was directed northward at the deeper sites and southward at the inshore sites. Near-bottom transport remained offshore at the deeper sites, but was lower, with negligible net cross-shore component at the shallow sites. The relative contribution of shoreward bedload transport was much larger. These changes in sediment transport outside the breaker zone are consistent with measured changes in beach and bar morphology.

Tidal, Residual, Intertidal Mudflat (TRIM) Model and its Applications to San Francisco Bay, California

USGS Publications Warehouse

Cheng, R.T.; Casulli, V.; Gartner, J.W.

1993-01-01

A numerical model using a semi-implicit finite-difference method for solving the two-dimensional shallow-water equations is presented. The gradient of the water surface elevation in the momentum equations and the velocity divergence in the continuity equation are finite-differenced implicitly, the remaining terms are finite-differenced explicitly. The convective terms are treated using an Eulerian-Lagrangian method. The combination of the semi-implicit finite-difference solution for the gravity wave propagation, and the Eulerian-Lagrangian treatment of the convective terms renders the numerical model unconditionally stable. When the baroclinic forcing is included, a salt transport equation is coupled to the momentum equations, and the numerical method is subject to a weak stability condition. The method of solution and the properties of the numerical model are given. This numerical model is particularly suitable for applications to coastal plain estuaries and tidal embayments in which tidal currents are dominant, and tidally generated residual currents are important. The model is applied to San Francisco Bay, California where extensive historical tides and current-meter data are available. The model calibration is considered by comparing time-series of the field data and of the model results. Alternatively, and perhaps more meaningfully, the model is calibrated by comparing the harmonic constants of tides and tidal currents derived from field data with those derived from the model. The model is further verified by comparing the model results with an independent data set representing the wet season. The strengths and the weaknesses of the model are assessed based on the results of model calibration and verification. Using the model results, the properties of tides and tidal currents in San Francisco Bay are characterized and discussed. Furthermore, using the numerical model, estimates of San Francisco Bay's volume, surface area, mean water depth, tidal prisms, and tidal excursions at spring and neap tides are computed. Additional applications of the model reveal, qualitatively the spatial distribution of residual variables. ?? 1993 Academic Press. All rights reserved.

Planetary and tidal wave-type oscillations in the ionospheric sporadic E layers over Tehran region

NASA Astrophysics Data System (ADS)

Karami, K.; Ghader, S.; Bidokhti, A. A.; Joghataei, M.; Neyestani, A.; Mohammadabadi, A.

2012-04-01

It is believed that in the lower ionosphere, particularly in the ionospheric sporadic E (Es) layers (90-130 km), the planetary and tidal wave-type oscillations in the ionized component indicate the planetary and tidal waves in the neutral atmosphere. In the present work, the presence of wave-type oscillations, including planetary and tidal waves in the ionospheric sporadic E layers over Tehran region is examined. Data measured by a digital ionosonde at the ionospheric station of the Institute of Geophysics, University of Tehran, from July 2006 to June 2007 are used to investigate seasonal variations of planetary and tidal waves activities. For the purpose of accurate comparison between different seasons, wavelet transform is applied to time series of foEs and h‧Es, namely, the critical frequency and virtual height of Es layers, respectively. The results show that the sporadic E layers over Tehran region are strongly under the influence of upward propagation of waves from below. More specifically, among diverse range of periodicities in the sporadic E layers, we found that diurnal (24 hours) and semidiurnal (12 hours) oscillations in all seasons for both parameters. Moreover, terdiurnal (8 hours) tide-like variation is observed during spring and summer for foEs parameter and summer and winter for h‧Es. Furthermore, the results show that diurnal tidal waves obtain their maximum activities during autumn and winter seasons, and their activities decrease during the late spring and summer. In addition, periods of about 2, 4, 6, 10, 14, and 16 days in our observation verifies the hypothesis of upward propagation of planetary waves from lower atmosphere to the ionosphere. Moreover, planetary waves have their maximum activities during equinox.

Tidal-cycle changes in oscillation ripples on the inner part of an estuarine sand flat

USGS Publications Warehouse

Dingler, J.R.; Clifton, H.E.

1984-01-01

Oscillation ripples form on subaqueous sand beds when wave-generated, near-bottom water motions are strong enough to move sand grains. The threshold of grain motion is the lower bound of the regime of oscillation ripples and the onset of sheet flow is the upper bound. Based on the relation between ripple spacing and orbital diameter, three types of symmetrical ripples occur within the ripple regime. In the lower part of the ripple regime (orbital ripples), spacing is proportional to orbital diameter; in the upper part (anorbital ripples) spacing is independent of orbital diameter. Between these regions occurs a transitional region (suborbital ripples). Oscillation ripples develop on a sandy tidal flat in Willapa Bay, Washington, as a result of waves traversing the area when it is submerged. Because wave energy is usually low within the bay, the ripples are primarily orbital in type. This means that their spacing should respond in a systematic way to changes in wave conditions. During the high-water parts of some tidal cycles, ripples near the beach decrease in spacing during the latter stage of the ebb tide while ripples farther offshore do not change. Observations made over several tidal cycles show that the zone of active ripples shifts on- or offshore in response to different wave conditions. Detailed bed profiles and current measurements taken during the high-water part of spring tides show the manner in which the oscillation ripples change with changes in orbital diameter. Changes in ripple spacing at the study site could be correlated with changes in orbital diameter in the manner suggested by the criterion for orbital ripples. However, there appeared to be a lag time between a decrease in orbital diameter and the corresponding decrease in ripple spacing. Absence of change during a tidal cycle could be attributed to orbital velocities below the threshold for grain motion that negated the effects of changes in orbital diameter. Because changes in sand-flat ripples depend both upon changes in orbital diameter and upon the magnitude of the orbital velocity, exposed ripples were not necessarily produced during the preceding high tide. In fact, some ripples may have been just produced, while others, farther offshore, may have been produced an unknown number of tides earlier. Therefore, when interpreting past wave conditions over tidal flats from low-tide ripples, one must remember that wave periods have to be short enough to produce velocities greater than the threshold velocity for the orbital diameters calculated from the observed ripple spacings. ?? 1984.

Equatorial Kelvin waves generated in the western tropical Pacific Ocean trigger mass and heat transport within the Middle America Trench off Costa Rica

NASA Astrophysics Data System (ADS)

Thomson, Richard E.; Davis, Earl E.

2017-07-01

Sequences of correlated seafloor temperature, current velocity, and acoustic backscatter events recorded at Ocean Drilling Program (ODP) sites at 4300 m depth in the Middle America Trench have been inferred to result from tidally induced turbidity currents generated in the vicinity of the 3300 m deep sill at the southern end of the trench. New data from the borehole observatories extend the temperature records to 11 years (November 2002 to December 2013) and confirm the highly episodic nature of the events. We present satellite altimetry data and ocean circulation model results to show that event timing is correlated with intraseasonal Kelvin wave motions in the equatorial Pacific. The observed temperature events had a mean (±1 standard deviation) occurrence interval of 61 (±24) days, which spans the periods of the first two baroclinic modes. Lag times between peak bottom water temperatures at the ODP sites and the passage of eastward-propagating Kelvin wave crests at locations in the eastern equatorial Pacific are consistent with the time for mode-1 waves to propagate to the southern end of the trench at a mean phase speed of 2.0 m s-1. Findings indicate that Kelvin wave currents augment tidal motions in the vicinity of the sill, triggering turbidity currents that travel northwestward along the trench axis at mean speeds of ˜0.1 m s-1. We conclude that mode-1 (or, possibly, mixed mode-1 and mode-2) baroclinic Kelvin waves generated by large-scale atmospheric processes in the western tropical Pacific lead to heat and mass transport deep within Middle America Trench in the eastern tropical Pacific.

Statistical Analysis of Acoustic Signal Propagating Through the South China Sea Basin

DTIC Science & Technology

2016-03-01

internal tidal constituents are observed in both spectra, and the diurnal (D) and semidiurnal (SD) internal waves ’ energy are strong. The spectrum is...bandwidths were utilized during the frequency smoothing process to ensure the reliability of the spectra in the meso-, tidal and internal wave scale...mooring temperature sensors capture the internal waves ’ energy, and six high amplitude peaks are observed in the spectra in the internal tidal band

Effects of wave-current interaction on storm surge in the Taiwan Strait: Insights from Typhoon Morakot

NASA Astrophysics Data System (ADS)

Yu, Xiaolong; Pan, Weiran; Zheng, Xiangjing; Zhou, Shenjie; Tao, Xiaoqin

2017-08-01

The effects of wave-current interaction on storm surge are investigated by a two-dimensional wave-current coupling model through simulations of Typhoon Morakot in the Taiwan Strait. The results show that wind wave and slope of sea floor govern wave setup modulations within the nearshore surf zone. Wave setup during Morakot can contribute up to 24% of the total storm surge with a maximum value of 0.28 m. The large wave setup commonly coincides with enhanced radiation stress gradient, which is itself associated with transfer of wave momentum flux. Water levels are to leading order in modulating significant wave height inside the estuary. High water levels due to tidal change and storm surge stabilize the wind wave and decay wave breaking. Outside of the estuary, waves are mainly affected by the current-induced modification of wind energy input to the wave generation. By comparing the observed significant wave height and water level with the results from uncoupled and coupled simulations, the latter shows a better agreement with the observations. It suggests that wave-current interaction plays an important role in determining the extreme storm surge and wave height in the study area and should not be neglected in a typhoon forecast.

Comparison of Water Turbine Characteristics using Different Blades in Darrieus Water Turbines used for Tidal Current Generations

NASA Astrophysics Data System (ADS)

Shiono, Mitsuhiro; Suzuki, Katsuyuki; Kiho, Seiji

The use of renewable energies has been focused on for preserving environments and coping with the shortage of future energy supplies. In oceans, a tide reverses its current direction every six hours, and the current velocity changes into a sine wave after a period of time. Tidal current generation uses a generator to produce energy, changing the kinetic energy of current into a turning force by setting a water turbine in the tidal current. Therefore, it is considered to be very advantageous to use a water turbine that can always revolve in a fixed direction without any influence from tidal current directions. Water turbines with these characteristics are known as Darrieus water turbines. The Darrieus water turbines were modified for water from turbines originally developed for windmills. Darrieus water turbines have a difficulty in starting, but these days Darrieus water turbines have been developed with spiral blades, which make it easy to get the turbines started. However, there are very few reports regarding Darrieus water turbines with spiral blades, and therefore their characteristics are unknown. From the above points of view, this study devises and investigates spiral blade-Darrieus water turbines to clarify their characteristics through hydrographic experiments, and at the same time, it compares the characteristics of spiral-blade Darrieus water turbines with those of straight-blade ones.

Hydrodynamic modeling and feasibility study of harnessing tidal power at the Bay of Fundy

NASA Astrophysics Data System (ADS)

Chang, Jen

Due to rising fuel costs and environmental concerns, energy generation from alternative power source has become one of the most important issues in energy policy. Tidal power is one of the alternative energy sources. The tidal range at the Bay of Fundy is the largest in the world (approximately 16 meters). It represents a prime location for harnessing tidal power using the daily rising and ebbing tide. In this study, a two dimensional finite element model has been developed and applied to simulate the tidal responses, including water level and flow velocity, in the Bay of Fundy region. The simulation results are used to choose the suitable location for energy development and to predict possible energy generated from different types of generation methods. Fluid motion is assumed to be governed by the shallow water equation since the wave length associated with tide is much longer than the water depth in the Bay of Fundy. By using a real time series of water elevation at the entrance of the bay, the computer model finds tidal response for each node in the study area, which is then verified by the observation record from several tidal gauge stations inside the bay. This study shows that the at-site cost of the energy for barrage type tidal power plants is around 0.065 to 0.097 per kWh at the recommended Shepody Bay, Cumberland Basin, and Cobequid Bay. The cost of energy for the current turbine type tidal power plants is 0.13/kWh to 0.24/kWh at the area with highest current velocity. Compared with the recent bill of the local power company, the at-site unit cost of energy from the barrage type of tidal power plant is feasible, but the environmental concerns of channel blocking by barrage present a formidable constraint. For the current turbine type of tidal power plant, even the most suitable sites are not financially feasible under current technology, but this type of power generation may become feasible as oil prices continue to increase and more efficient turbines become available.

The Sidebands of the Equatorial Electrojet: General Characteristic of the Westward Currents, as Deduced From CHAMP

NASA Astrophysics Data System (ADS)

Zhou, Yun-Liang; Lühr, Hermann; Alken, Patrick

2018-02-01

Based on 5 years (2001-2005) of magnetic field measurements made by the CHAMP satellite, latitudinal profiles of the equatorial electrojet (EEJ) have been derived. This study provides a comprehensive characterization of the reverse current EEJ sidebands. These westward currents peak at ±5° quasi-dipole latitude with typical amplitudes of 35% of the main EEJ. The diurnal amplitude variation is quite comparable with that of the EEJ. Similarly to the EEJ, the intensity is increasing with solar EUV flux, but with a steeper slope, indicating that not only the conductivity plays a role. For the longitude distribution we find, in general, larger amplitudes in the Western than in the Eastern Hemisphere. It is presently a common understanding that the reverse current EEJ sidebands are generated by eastward zonal winds at altitudes above about 120 km. In particular, a positive vertical gradient of wind speed generates westward currents at magnetic latitudes outside of 2° dip latitude. Interesting information about these features can be deduced from the sidebands' tidal characteristics. The longitudinal variation of the amplitude is dominated by a wave-1 pattern, which can primarily be attributed to the tidal components SPW1 and SW3. In case of the hemispheric amplitude differences these same two wave-1 components dominate. The ratio between sideband amplitude and main EEJ is largely controlled by the tidal features of the EEJ. The longitudinal patterns of the latitude, where the sidebands peak, resemble to some extent those of the amplitude. Current densities become larger when the peaks move closer to the magnetic equator.

Dynamical Tidal Response of a Rotating Neutron Star

NASA Astrophysics Data System (ADS)

Landry, Philippe; Poisson, Eric

2017-01-01

The gravitational wave phase of a neutron star (NS) binary is sensitive to the deformation of the NS that results from its companion's tidal influence. In a perturbative treatment, the tidal deformation can be characterized by a set of dimensionless constants, called Love numbers, which depend on the NS equation of state. For static NSs, one type of Love number encodes the response to gravitoelectric tidal fields (associated with mass multipole moments), while another does likewise for gravitomagnetic fields (associated with mass currents). A NS subject to a gravitomagnetic tidal field develops internal fluid motions through gravitomagnetic induction; the fluid motions are irrotational, provided the star is non-rotating. When the NS is allowed to rotate, the situation is complicated by couplings between the tidal field and the star's spin. The problem becomes tractable in the slow-rotation limit. In this case, the fluid motions induced by an external gravitomagnetic field are fully dynamical, even if the tidal field is stationary: interior metric and fluid variables are time-dependent, and vary on the timescale of the rotation period. Remarkably, the exterior geometry of the NS remains time-independent.

Analytical Model of Inlet Growth and Equilibrium Cross-Sectional Area

DTIC Science & Technology

2016-04-01

performance in a real-world setting. BACKGROUND: Long-term inlet stability in bar-built systems is determined by the tidal and wave forces that...across the node was limited due to convergence of the two incoming tidal waves . As such, the equivalent bay area was calculated using the midpoint as a...sediment transport is driven by tides and does not incorporate other forcing and associated sediment pathways. The ratio of wave to tidal energy is an

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinto, F. T.; Iglesias, G.; Santos, P. R.

Marine renewable energy (MRE) is generates from waves, currents, tides, and thermal resources in the ocean. MRE has been identified as a potential commercial-scale source of renewable energy. This special topic presents a compilation of works selected from the 3rd IAHR Europe Congress, held in Porto, Portugal, in 2014. It covers different subjects relevant to MRE, including resource assessment, marine energy sector policies, energy source comparisons based on levelized cost, proof-of-concept and new-technology development for wave and tidal energy exploitation, and assessment of possible inference between wave energy converters (WEC).

Hazard assessment of the Tidal Inlet landslide and potential subsequent tsunami, Glacier Bay National Park, Alaska

USGS Publications Warehouse

Wieczorek, G.F.; Geist, E.L.; Motyka, R.J.; Jakob, M.

2007-01-01

An unstable rock slump, estimated at 5 to 10????????10 6 m3, lies perched above the northern shore of Tidal Inlet in Glacier Bay National Park, Alaska. This landslide mass has the potential to rapidly move into Tidal Inlet and generate large, long-period-impulse tsunami waves. Field and photographic examination revealed that the landslide moved between 1892 and 1919 after the retreat of the Little Ice Age glaciers from Tidal Inlet in 1890. Global positioning system measurements over a 2-year period show that the perched mass is presently moving at 3-4 cm annually indicating the landslide remains unstable. Numerical simulations of landslide-generated waves suggest that in the western arm of Glacier Bay, wave amplitudes would be greatest near the mouth of Tidal Inlet and slightly decrease with water depth according to Green's law. As a function of time, wave amplitude would be greatest within approximately 40 min of the landslide entering water, with significant wave activity continuing for potentially several hours. ?? 2007 Springer-Verlag.

Connections Among the Spatial and Temporal Structures in Tidal Currents, Internal Bores, and Surficial Sediment Distributions Over the Shelf off Palos Verdes, California

USGS Publications Warehouse

Noble, Marlene A.; Rosenberger, Kurt J.; Xu, Jingping; Signell, Richard P.; Steele, Alex

2009-01-01

The topography of the Continental Shelf in the central portion of the Southern California Bight has rapid variations over relatively small spatial scales. The width of the shelf off the Palos Verdes peninsula, just northwest of Los Angeles, California, is only 1 to 3 km. About 7 km southeast of the peninsula, the shelf within San Pedro Bay widens to about 20 km. In 2000, the Los Angeles County Sanitation District began deploying a dense array of moorings in this complex region of the central Southern California Bight to monitor local circulation patterns. Moorings were deployed at 13 sites on the Palos Verdes shelf and within the northwestern portion of San Pedro Bay. At each site, a mooring supported a string of thermistors and an adjacent bottom platform housed an Acoustic Doppler Current Profiler. These instruments collected vertical profiles of current and temperature data continuously for one to two years. The variable bathymetry in the region causes rapid changes in the amplitudes and spatial structures of barotropic tidal currents, internal tidal currents, and in the associated nonlinear baroclinic currents that occur at approximate tidal frequencies. The largest barotropic tidal constituent is M2, the principal semidiurnal tide. The amplitude of this tidal current changes over fairly short along-shelf length scales. Tidal-current amplitudes are largest in the transition region between the two shelves; they increase from about 5 cm/s over the northern San Pedro shelf to nearly 10 cm/s on the southern portion of the Palos Verdes Shelf. Tidal-current amplitudes are then reduced to less than 2 cm/s over the very narrow section of the northern Palos Verdes shelf that lies just 6 km upcoast of the southern sites. Models suggest that the amplitude of the barotropic M2 tidal currents, which propagate toward the northwest primarily as a Kelvin wave, is adjusting to the short topographic length scales in the region. Semidiurnal sea-level oscillations are, as expected, independent of these topographic variations; they have a uniform amplitude and phase structure over the entire region. Because the cross-shelf angle of the seabed over most of the Palos Verdes shelf is 1 to 3 degrees, which is critical for the local generation and/or enhancement of nonlinear characteristics in semidiurnal internal tides, some internal tidal-current events have strong asymmetric current oscillations that are enhanced near the seabed. Near-bottom currents in these events are directed primarily offshore with amplitudes that exceed 30 cm/s. The spatial patterns in these energetic near-bottom currents have fairly short-length scales. They are largest over the inner shelf and in the transition region between the Palos Verdes and San Pedro shelves. This spatial pattern is similar to that found in the barotropic tidal currents. Because these baroclinic currents have an approximate tidal frequency, an asymmetric vertical structure, and a somewhat stable phase, they can produce a non-zero depth-mean flow for periods of a few months. These baroclinic currents can interact with the barotropic tidal current and cause an apparent increase (or decrease) in the estimated barotropic tidal-current amplitude. The apparent amplitude of the barotropic tidal current may change by 30 to 80 percent or more in a current record that is less than three months long. The currents and surficial sediments in this region are in dynamic equilibrium in that the spatial patterns in bottom stresses generated by near-bed currents from surface tides, internal tides, and internal bores partly control the spatial patterns in the local sediments. Coarser sediments are found in the regions with enhanced bottom stresses (that is, over the inner shelf and in the region between the Palos Verdes and San Pedro shelves). Finer sediments are found over the northwestern portion of the Palos Verdes shelf, where near-bottom currents are relatively weak. The nonlinear asymmetries in the i

Tidal dissipation and evolution of white dwarfs around massive black holes: an eccentric path to tidal disruption

NASA Astrophysics Data System (ADS)

Vick, Michelle; Lai, Dong; Fuller, Jim

2017-06-01

A white dwarf (WD) captured into a high-eccentricity orbit around a massive black hole (MBH) may undergo many pericentre passages before tidal disruption. During these passages, the tidal potential of the MBH excites internal oscillations or waves in the WD, and the dissipation of these oscillations can significantly influence the physical properties of the WD prior to its disruption. We calculate the amplitude of the tidally excited gravity (buoyancy) waves in the WD as a function of the pericentre distance and eccentricity for realistic WD models, under the assumption that these outgoing gravity waves are efficiently dissipated in the outer layers of the WD by non-linear effects or radiative damping. We obtain fitting formulae for the tidal energy and angular momentum transfer rates as well as the tidal heating rate. We find that these dynamical tides are much weaker than gravitational radiation in driving the orbital decay of the WD-MBH binary, and they are also inefficient in changing the WD spin during the orbital evolution. Incorporating our computed tidal dissipation rate into a mesa-based WD evolution code, we find that tidal heating can lead to appreciable brightening of the WD and may induce runaway fusion in the hydrogen envelope well before the WD undergoes tidal disruption.

Contribution to the study of the Ria de Aveiro inlet morphodynamics =

NASA Astrophysics Data System (ADS)

Plecha, Sandra Marta Nobre

Over the years it was observed at the Ria de Aveiro lagoon inlet, near the head of the north breakwater, a depth increase that might threaten the stability of this structure. A trend of accretion in the navigation channel of this lagoon is observed, endangering the navigation in this region. In order to understand the origin of these and other trends observed, the knowledge of the sediment transport in the study area is imperative. The main aim of this work is understanding the dominant physical processes in the sediment transport of sediment at the Ria de Aveiro lagoon inlet and adjacent area, improving knowledge of this region morphodynamics. The methodology followed in this study consisted in the analyzes of the topohydrographic surveys performed by the Administration of the Aveiro Harbor, and in the numerical simulations results performed with the morphodynamic modeling system MORSYS2D. The analysis of the surveys was performed by studying the temporal evolution of the bathymetry. The numerical analysis was based on the implementation of the model at the study area, sensitivity analysis of the formulations used to compute the sediment transport to the variation of input parameters (e.g. depth, sediment size, tidal currents) and analysis of the sediment fluxes and bathymetric changes predicted. The simulations considered as sediment transport forcing the tidal currents only and the coupled forcing of tides and waves. Considering the wave effect as sediment transport forcing, both monochromatic waves and a wave regime were simulated. The results revealed that the observed residual sediment transport patterns are generated due to the channel configuration. Inside the lagoon the fluxes are mainly induced by the tidal currents action, restricting the action of waves to the inlet and adjacent coast. In the navigation channel the residual sediment fluxes predicted are directed offshore with values between 7 and 40 m3/day generating accretions of approximately 10 m3/day for the shallower region and 35 m3/day for the region between the tidal gauge and the triangulo das mares. At the inlet, the residual fluxes are approximately 30 m3/day inducing trends of erosion of approximately 20 m3/day. At the North side of the nearshore accretion is predicted, while at the South side is predicted erosion, at the rates of 250 and 1500 m3/day, respectively. It was also concluded that the waves with higher contribution to the residual sediment uxes are those with heights between 4 and 5 m. However, the storm waves with heights bigger than 5 m, despite their 10% of frequency of occurrence are responsible for 25% of the observed sediment transport.

Internal wave observations made with an airborne synthetic aperture imaging radar

NASA Technical Reports Server (NTRS)

Elachi, C.; Apel, J. R.

1976-01-01

Synthetic aperture L-band radar flown aboard the NASA CV-990 has observed periodic striations on the ocean surface off the coast of Alaska which have been interpreted as tidally excited oceanic internal waves of less than 500 m length. These radar images are compared to photographic imagery of similar waves taken from Landsat 1. Both the radar and Landsat images reveal variations in reflectivity across each wave in a packet that range from low to high to normal. The variations point to the simultaneous existence of two mechanisms for the surface signatures of internal waves: roughening due to wave-current interactions, and smoothing due to slick formation.

Investigation of the environmental change pattern of Japan

NASA Technical Reports Server (NTRS)

Maruyasu, T. (Principal Investigator)

1973-01-01

The author has identified the following significant results. ERTS-1 imagery clearly identifies the relationships between the status of erosion, effluent patterns affected by the coastal current, and the cultural construction activities. Simple photographic techniques can be used for detecting water mass distribution separately from cloud cover and also noise caused by reflected sunlight from wave surfaces. Polluted water does not diffuse continuously into the oceanic water, but forms masses in the water in the Kuroshio area. The polluted or turbid water in the area just north of the Tomogashima Channel, the south outlet of the Osaka Bay, shows that the northward tidal current runs in a clockwise eddy at the tidal period when the imagery was taken. Such an eddy-like pattern of tidal current had never been revealed by conventional oceanographic data. A front between an oceanic water mass and a polluted water mass runs in a NW-SE direction in the central part of the Osaka Bay. The patterns of turbid water discharged from the Kii River and Yoshino River show a northward tidal current in the North Kii Straits. The pattern of lighter turbid or polluted water located in the northwest region of the North Kii straits suggests the existence of a clockwise eddy in the straits.

Character, distribution, and ecological significance of storm wave-induced scour in Rhode Island Sound, USA

USGS Publications Warehouse

McMullen, Katherine Y.; Poppe, Lawrence J.; Parker, Castle E.

2015-01-01

Multibeam bathymetry, collected during NOAA hydrographic surveys in 2008 and 2009, is coupled with USGS data from sampling and photographic stations to map the seabed morphology and composition of Rhode Island Sound along the US Atlantic coast, and to provide information on sediment transport and benthic habitats. Patchworks of scour depressions cover large areas on seaward-facing slopes and bathymetric highs in the sound. These depressions average 0.5-0.8 m deep and occur in water depths reaching as much as 42 m. They have relatively steep well-defined sides and coarser-grained floors, and vary strongly in shape, size, and configuration. Some individual scour depressions have apparently expanded to combine with adjacent depressions, forming larger eroded areas that commonly contain outliers of the original seafloor sediments. Where cobbles and scattered boulders are present on the depression floors, the muddy Holocene sands have been completely removed and the winnowed relict Pleistocene deposits exposed. Low tidal-current velocities and the lack of obstacle marks suggest that bidirectional tidal currents alone are not capable of forming these features. These depressions are formed and maintained under high-energy shelf conditions owing to repetitive cyclic loading imposed by high-amplitude, long-period, storm-driven waves that reduce the effective shear strength of the sediment, cause resuspension, and expose the suspended sediments to erosion by wind-driven and tidal currents. Because epifauna dominate on gravel floors of the depressions and infauna are prevalent in the finer-grained Holocene deposits, it is concluded that the resultant close juxtaposition of silty sand-, sand-, and gravel-dependent communities promotes regional faunal complexity. These findings expand on earlier interpretations, documenting how storm wave-induced scour produces sorted bedforms that control much of the benthic geologic and biologic diversity in Rhode Island Sound.

Physical processes in a coupled bay-estuary coastal system: Whitsand Bay and Plymouth Sound

NASA Astrophysics Data System (ADS)

Uncles, R. J.; Stephens, J. A.; Harris, C.

2015-09-01

Whitsand Bay and Plymouth Sound are located in the southwest of England. The Bay and Sound are separated by the ∼2-3 km-wide Rame Peninsula and connected by ∼10-20 m-deep English Channel waters. Results are presented from measurements of waves and currents, drogue tracking, surveys of salinity, temperature and turbidity during stratified and unstratified conditions, and bed sediment surveys. 2D and 3D hydrodynamic models are used to explore the generation of tidally- and wind-driven residual currents, flow separation and the formation of the Rame eddy, and the coupling between the Bay and the Sound. Tidal currents flow around the Rame Peninsula from the Sound to the Bay between approximately 3 h before to 2 h after low water and form a transport path between them that conveys lower salinity, higher turbidity waters from the Sound to the Bay. These waters are then transported into the Bay as part of the Bay-mouth limb of the Rame eddy and subsequently conveyed to the near-shore, east-going limb and re-circulated back towards Rame Head. The Simpson-Hunter stratification parameter indicates that much of the Sound and Bay are likely to stratify thermally during summer months. Temperature stratification in both is pronounced during summer and is largely determined by coastal, deeper-water stratification offshore. Small tidal stresses in the Bay are unable to move bed sediment of the observed sizes. However, the Bay and Sound are subjected to large waves that are capable of driving a substantial bed-load sediment transport. Measurements show relatively low levels of turbidity, but these respond rapidly to, and have a strong correlation with, wave height.

Tilt Current Meter Field Validation in the Surf Zone

NASA Astrophysics Data System (ADS)

Anarde, K.; Myres, H.; Figlus, J.

2016-12-01

Tilt current meters (TCMs) are a low-cost way of measuring current velocities in coastal waters. They consist of a slightly buoyant floater, tilt sensor assembly, and internal logger tethered to a fixed base. TCMs measure the tilt of the sensor induced by the forces of the flowing water to infer local current velocity. They have been successfully deployed to measure unidirectional flows in rivers and slowly oscillating flows in tidally influenced bodies of water where the inertia of the instrument does not create a problem. Here we attempt to validate an array of TCMs for use in the surf zone where waves, wave bores, and alongshore currents dominate the hydrodynamics in relatively shallow water (0.3 - 2.0 m) with relatively high oscillatory frequencies. A series of test deployments using seven measuring pods outfitted with TCMs and pressure transducers were conducted in the surf zone off Galveston Island, Texas. Field experiments were supported by laboratory tests of the instrument assemblies in a moveable-bed wave flume. Instrument pod design was optimized over the series of tests to minimize issues caused by scouring, sedimentation, and overturning. The end design consists of a low-profile concrete base plate secured to the bed by sand stakes. Field measurements of tilt and bearing were calibrated against co-located acoustic Doppler velocimeter (ADV) and wave-current profiler (ADCP) measurements as well as laboratory-supplied calibration curves. While optimization of the setup is ongoing, the initial field studies show good correlation between instrument pairs. If successfully validated, the TCMs will be used as part of an instrument array designed to measure overland flow dynamics during extreme storms. Other potential uses include detailed analysis of spatial and temporal gradients in nearshore hydrodynamics such as the complex flow scenarios through tidal inlets and around barrier islands.

How Do Tides and Tsunamis Interact in a Highly Energetic Channel? The Case of Canal Chacao, Chile

NASA Astrophysics Data System (ADS)

Winckler, Patricio; Sepúlveda, Ignacio; Aron, Felipe; Contreras-López, Manuel

2017-12-01

This study aims at understanding the role of tidal level, speed, and direction in tsunami propagation in highly energetic tidal channels. The main goal is to comprehend whether tide-tsunami interactions enhance/reduce elevation, currents speeds, and arrival times, when compared to pure tsunami models and to simulations in which tides and tsunamis are linearly superimposed. We designed various numerical experiments to compute the tsunami propagation along Canal Chacao, a highly energetic channel in the Chilean Patagonia lying on a subduction margin prone to megathrust earthquakes. Three modeling approaches were implemented under the same seismic scenario: a tsunami model with a constant tide level, a series of six composite models in which independent tide and tsunami simulations are linearly superimposed, and a series of six tide-tsunami nonlinear interaction models (full models). We found that hydrodynamic patterns differ significantly among approaches, being the composite and full models sensitive to both the tidal phase at which the tsunami is triggered and the local depth of the channel. When compared to full models, composite models adequately predicted the maximum surface elevation, but largely overestimated currents. The amplitude and arrival time of the tsunami-leading wave computed with the full model was found to be strongly dependent on the direction of the tidal current and less responsive to the tide level and the tidal current speed. These outcomes emphasize the importance of addressing more carefully the interactions of tides and tsunamis on hazard assessment studies.

Migrating diurnal tide variability induced by propagating planetary waves

NASA Astrophysics Data System (ADS)

Chang, Loren C.

The migrating diurnal tide is one of the dominant dynamical features in the low latitudes of the Earth's Mesosphere and Lower Thermosphere (MLT) region, representing the atmospheric response to the largest component of solar forcing, propagating upwards from excitation regions in the lower atmosphere. Ground-based observations of the tide have resolved short term variations attributed to nonlinear interactions between the tide and planetary waves also in the region. However, the conditions, effects, and mechanisms of a planetary wave - tidal interaction are still unclear. These questions are addressed using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) to examine two types of planetary waves, known to attain significant amplitudes in the low latitude and equatorial region where the migrating diurnal tide is dominant. The quasi-two day wave (QTDW) can rapidly amplify to large amplitudes from the summer hemisphere during post-solstice periods, while ultra fast Kelvin (UFK) waves occur sporadically in the temperature and zonal wind fields of the equatorial lower thermosphere. While child waves resulting from a nonlinear interaction are resolved in both cases, the response of the tidal structure and amplitudes to the two planetary waves differs significantly. In the case of the QTDW, the migrating diurnal tide displays a general amplitude decrease of 20 - 40%, as well as a shortening of vertical wavelength by roughly 4 km. Nonlinear advection is found to result in energy transfer to and from the tide, resulting in latitudinal smoothing of the tidal structure. The QTDW also produces significant changes to the mean zonal winds in the equator and at summer mid to high latitudes that can also account for changes in tidal amplitude and vertical wavelength. Filtering of gravity waves by the altered mean winds can also result in changes to the zonal mean zonal winds in the tropics. However, gravity wave momentum forcing on the tide is smaller than the advective tendencies throughout most of the MLT region, and cannot iv directly account for the changes in the tide during the QTDW model simulation. In the case of the UFK wave, baseline tidal amplitudes are found to show much smaller changes of 10% or less, despite the larger amplitudes of the UFK wave in the lower thermosphere region compared to the QTDW. Analysis of the nonlinear advective tendencies shows smaller magnitudes than those in the the case of the QTDW, with interaction regions limited primarily to a smaller region in latitude and altitude. Increased tidal convergence in the tropical lower thermosphere is attributed to eastward forcing of the background zonal mean winds by the UFK wave. Increasing the UFK wave forcing by an order of magnitude, although unrealistic, results in changes to the tide comparable in magnitude to the case of the QTDW. While child waves generated by nonlinear advection are present with both of the propagating planetary waves examined, the QTDW produces much greater tidal variability through both nonlinear and linear advection due to its broader horizontal and vertical structure, compared to the UFK wave. Planetary wave induced background atmosphere changes can also drive tidal variability, suggesting that changes to the tidal response in the MLT can also result from this indirect coupling mechanism, in addition to nonlinear advection.

Weak wind-wave/tide interaction over fixed and moveable bottoms: a formulation and some preliminary results

NASA Astrophysics Data System (ADS)

Kagan, B. A.; Alvarez, O.; Izquierdo, A.

2005-05-01

The formulation of weak wind-wave/low-frequency current interaction is discussed comprehensively as applied to fixed- and moveable-bottom cases. It involves (1) a dependence of the drag coefficient on the ratio between wave and current bottom friction velocity amplitudes, (2) the resistance law for the oscillatory, rough, turbulent bottom boundary layer (BBL) which accounts for the usually neglected effects of rotation and the phase difference between the bottom stress and the friction-free current velocity, (3) the expression for the BBL depth in terms of the bottom Rossby number and (4) the bottom roughness predictor of Grant and Madsen (J. Geophys. Res., 87 (1982) 469) in the version of Tolman (J. Phys. Oceanogr., 24 (1994) 994). The formulation is implemented in the UCA (University of Cadiz) 2D nonlinear, high-resolution, hydrodynamic model and used to study the influence of wind-wave/tide interaction, bottom mobility and the improved flow-resistance description on the M 2 tidal dynamics of Cadiz Bay. The inclusion of either of the first two factors can cause the drag coefficient to increase significantly over its reference value. If the third factor is included, changes in the drag coefficient are quite moderate. This is because the effect of rotation is opposite in sign to the effect of phase difference, so that these effects taken together very nearly balance. The reason why bottom mobility has such an important influence on shallow-water tidal dynamics as wind-wave/tide interaction has, is the occurrence of the large irregular variations in the drag coefficient that accompany sediment motion.

Field observation and analysis of wave-current-sediment movement in Caofeidian Sea area in the Bohai Bay, China

NASA Astrophysics Data System (ADS)

Zuo, Li-qin; Lu, Yong-jun; Wang, Ya-ping; Liu, Huai-xiang

2014-06-01

In order to study the mechanism of flow-sediment movement, it is essential to obtain measured data of water hydrodynamic and sediment concentration process with high spatial and temporal resolution in the bottom boundary layer (BBL). Field observations were carried out in the northwest Caofeidian sea area in the Bohai Bay. Near 2 m isobath (under the lowest tidal level), a tripod system was installed with AWAC (Acoustic Wave And Current), ADCP (Acoustic Doppler Current Profilers), OBS-3A (Optical Backscatter Point Sensor), ADV (Acoustic Doppler Velocimeters), etc. The accurate measurement of the bottom boundary layer during a single tidal period was carried out, together with a long-term sediment concentration measurement under different hydrological conditions. All the measured data were used to analyze the characteristics of wave-current-sediment movement and the BBL. Analysis was performed on flow structure, shear stress, roughness, eddy viscosity and other parameters of the BBL. Two major findings were made. Firstly, from the measured data, the three-layer distribution model of the velocity profiles and eddy viscosities in the wave-current BBL are proposed in the observed sea area; secondly, the sediment movement is related closely to wind-waves in the muddy coast area where sediment is clayey silt: 1) The observed suspended sediment concentration under light wind conditions is very low, with the peak value generally smaller than 0.1 kg/m3 and the average value being 0.03 kg/m3; 2) The sediment concentration increases continuously under the gales over 6-7 in Beaufort scale, under a sustained wind action. The measured peak sediment concentration at 0.4 m above the seabed is 0.15-0.32 kg/m3, and the average sediment concentration during wind-wave action is 0.08-0.18 kg/m3, which is about 3-6 times the value under light wind conditions. The critical wave height signaling remarkable changes of sediment concentration is 0.5 m. The results show that the suspended load sediment concentration is mainly influenced by wave-induced sediment suspension.

Tidal dissipation in rotating fluid bodies: the presence of a magnetic field

NASA Astrophysics Data System (ADS)

Lin, Yufeng; Ogilvie, Gordon I.

2018-02-01

We investigate effects of the presence of a magnetic field on tidal dissipation in rotating fluid bodies. We consider a simplified model consisting of a rigid core and a fluid envelope, permeated by a background magnetic field (either a dipolar field or a uniform axial field). The wave-like tidal responses in the fluid layer are in the form of magnetic Coriolis waves, which are restored by both the Coriolis force and the Lorentz force. Energy dissipation occurs through viscous damping and Ohmic damping of these waves. Our numerical results show that the tidal dissipation can be dominated by Ohmic damping even with a weak magnetic field. The presence of a magnetic field smooths out the complicated frequency dependence of the dissipation rate, and broadens the frequency spectrum of the dissipation rate, depending on the strength of the background magnetic field. However, the frequency-averaged dissipation is independent of the strength and structure of the magnetic field, and of the dissipative parameters in the approximation that the wave-like response is driven only by the Coriolis force acting on the non-wavelike tidal flow. Indeed, the frequency-averaged dissipation quantity is in good agreement with previous analytical results in the absence of magnetic fields. Our results suggest that the frequency-averaged tidal dissipation of the wave-like perturbations is insensitive to detailed damping mechanisms and dissipative properties.

Hindcast of breaking waves and its impact at an island sheltered coast, Karwar

NASA Astrophysics Data System (ADS)

Dora, G. Udhaba; Kumar, V. Sanil

2018-01-01

Variability in the characteristics of depth-induced wave breakers along a non-uniform coastal topography and its impact on the morpho-sedimentary processes is examined at the island sheltered wave-dominated micro-tidal coast, Karwar, west coast of India. Waves are simulated using the coupled wind wave model, SWAN nested in WAVEWATCH III, forced by the reanalysis winds from different sources (NCEP/NCAR, ECMWF, and NCEP/CFSR). Impact of the wave breakers is evaluated through mean longshore current and sediment transport for various wave energy conditions across different coastal morphology. Study revealed that the NCEP/CFSR wind is comparatively reasonable in simulation of nearshore waves using the SWAN model nested by 2D wave spectra generated from WAVEWATCH III. The Galvin formula for estimating mean longshore current using the crest wave period and the Kamphuis approximation for longshore sediment transport is observed realistically at the sheltered coastal environment while the coast interacts with spilling and plunging breakers.

NREL Deploys Wave and Tidal Measurement Buoys | News | NREL

Science.gov Websites

various wave and tidal models, and in turn, reduce risks for developers. These buoys allow researchers to "better understand the limitations and errors in existing global wave models," says Kilcher using NREL, laboratory, and U.S. Department of Energy published models, the team identified likely

Monitoring and modeling nearshore dredge disposal for indirect beach nourishment, Ocean Beach, San Francisco

USGS Publications Warehouse

Barnard, Patrick L.; Hanes, Daniel M.; Lescinski, Jamie; Elias, Edwin

2007-01-01

Nearshore dredge disposal was performed during the summer of 2005 at Ocean Beach, San Francisco, CA, a high energy tidal and wave environment. This trial run was an attempt to provide a buffer to a reach of coastline where wave attack during the winter months has had a severe impact on existing sewage infrastructure. Although the subsequent beach response was inconclusive, after one year the peak of the disposal mound had migrated ~100 m toward the shore, providing evidence that annual dredge disposal at this site could be beneficial over the long-term by at the very least providing: 1) additional wave dissipation during storms 2) compatible sediment to feed nearshore bars, 3) sediment cover on an exposed sewage outfall pipe, and 4) a viable alternative to the shoaling offshore disposal site. Numerical modeling suggests that despite the strong tidal currents in the region, wave forcing is the dominant factor moving the sediment slowly toward shore, and placing sediment at just slightly shallower depths (e.g. 9 m) in the future would have a more immediate impact.

Homogeneous wave turbulence driven by tidal flows

NASA Astrophysics Data System (ADS)

Favier, B.; Le Reun, T.; Barker, A.; Le Bars, M.

2017-12-01

When a moon orbits around a planet, the rotation of the induced tidal bulge drives a homogeneous, periodic, large-scale flow. The combination of such an excitation with the rotating motion of the planet has been shown to drive parametric resonance of a pair of inertial waves in a mechanism called the elliptical instability. Geophysical fluid layers can also be stratified: this is the case for instance of the Earth's oceans and, as suggested by several studies, of the upper part of the Earth's liquid Outer Core. We thus investigate the stability of a rotating and stratified layer undergoing tidal distortion in the limit where either rotation or stratification is dominant. We show that the periodic tidal flow drives a parametric subharmonic resonance of inertial (resp. internal) waves in the rotating (resp. stratified) case. The instability saturates into a wave turbulence pervading the whole fluid layer. In such a state, the instability mechanism conveys the tidal energy from the large scale tidal flow to the resonant modes, which then feed a succession of triadic resonances also generating small spatial scales. In the rotating case, we observe a kinetic energy spectrum with a k-2 slope for which the Coriolis force is dominant at all spatial scales. In the stratified case, where the timescale separation is increased between the tidal excitation and the Brunt-Väisälä frequencies, the temporal spectrum decays with a ω-2 power law up to the cut-off frequency beyond which waves do not exist. This result is reminiscent of the Garrett and Munk spectrum measured in the oceans and theoretically described as a manifestation of internal wave turbulence. In addition to revealing an instability driving homogeneous turbulence in geophysical fluid layers, our approach is also an efficient numerical tool to investigate the possibly universal properties of wave turbulence in a geophysical context.

The wave and tidal resource of Scotland

NASA Astrophysics Data System (ADS)

Neill, Simon; Vogler, Arne; Lewis, Matt; Goward-Brown, Alice

2017-04-01

As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to re-assess the wave and tidal resource of a region. This is particularly true for Scotland - a leading nation that the international community monitors for developments in the marine renewable energy industry, and which has witnessed much progress in the sector over the last decade. With 7 leased wave and 17 leased tidal sites, Scotland is well poised to generate significant levels of electricity from its abundant natural marine resources. In this review of Scotland's wave and tidal resource, I present the theoretical and technical resource, and provide an overview of commercial progress. I also discuss issues that affect future development of the marine energy seascape in Scotland, applicable to other regions of the world, including the potential for developing lower energy sites, and grid connectivity.

Gravitational waveforms for neutron star binaries from binary black hole simulations

NASA Astrophysics Data System (ADS)

Barkett, Kevin; Scheel, Mark A.; Haas, Roland; Ott, Christian D.; Bernuzzi, Sebastiano; Brown, Duncan A.; Szilágyi, Béla; Kaplan, Jeffrey D.; Lippuner, Jonas; Muhlberger, Curran D.; Foucart, Francois; Duez, Matthew D.

2016-02-01

Gravitational waves from binary neutron star (BNS) and black hole/neutron star (BHNS) inspirals are primary sources for detection by the Advanced Laser Interferometer Gravitational-Wave Observatory. The tidal forces acting on the neutron stars induce changes in the phase evolution of the gravitational waveform, and these changes can be used to constrain the nuclear equation of state. Current methods of generating BNS and BHNS waveforms rely on either computationally challenging full 3D hydrodynamical simulations or approximate analytic solutions. We introduce a new method for computing inspiral waveforms for BNS/BHNS systems by adding the post-Newtonian (PN) tidal effects to full numerical simulations of binary black holes (BBHs), effectively replacing the nontidal terms in the PN expansion with BBH results. Comparing a waveform generated with this method against a full hydrodynamical simulation of a BNS inspiral yields a phase difference of <1 radian over ˜15 orbits. The numerical phase accuracy required of BNS simulations to measure the accuracy of the method we present here is estimated as a function of the tidal deformability parameter λ .

Tidal flushing and wind driven circulation of Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia) from in situ observations and numerical modelling.

PubMed

Dumas, F; Le Gendre, R; Thomas, Y; Andréfouët, S

2012-01-01

Hydrodynamic functioning and water circulation of the semi-closed deep lagoon of Ahe atoll (Tuamotu Archipelago, French Polynesia) were investigated using 1 year of field data and a 3D hydrodynamical model. Tidal amplitude averaged less than 30 cm, but tide generated very strong currents (2 ms(-1)) in the pass, creating a jet-like circulation that partitioned the lagoon into three residual circulation cells. The pass entirely flushed excess water brought by waves-induced radiation stress. Circulation patterns were computed for climatological meteorological conditions and summarized with stream function and flushing time. Lagoon hydrodynamics and general overturning circulation was driven by wind. Renewal time was 250 days, whereas the e-flushing time yielded a lagoon-wide 80-days average. Tide-driven flush through the pass and wind-driven overturning circulation designate Ahe as a wind-driven, tidally and weakly wave-flushed deep lagoon. The 3D model allows studying pearl oyster larvae dispersal in both realistic and climatological conditions for aquaculture applications. Copyright © 2012 Elsevier Ltd. All rights reserved.

Influence of San Gabriel submarine canyon on narrow-shelf sediment dynamics, southern California

USGS Publications Warehouse

Karl, Herman A.

1980-01-01

A conceptual model attributes the PTC to modification of shelf circulation patterns by San Gabriel Canyon. Surface waves diverge over the canyon head resulting in differential wave set up at the shore face. This forces back turbid nearshore water for a distance of a few kilometers toward the canyon. At some point on the shelf, seaward nearshore flow overlaps offshore currents generated or modified by internal waves focused onto the shelf by the canyon and/or turbulent eddies produced by flow separation in currents moving across the canyon axis. At times, these subtle processes overprint tidal and wind-driven currents and thereby create the PTC. The model suggests that canyons heading several kilometers from shore can have a regulatory effect on narrow-shelf sediment dynamics.

Small scale currents and ocean wave heights: from today's models to future satellite observations with CFOSAT and SKIM

NASA Astrophysics Data System (ADS)

Ardhuin, Fabrice; Gille, Sarah; Menemenlis, Dimitris; Rocha, Cesar; Rascle, Nicolas; Gula, Jonathan; Chapron, Bertrand

2017-04-01

Tidal currents and large oceanic currents, such as the Agulhas, Gulf Stream and Kuroshio, are known to modify ocean wave properties, causing extreme sea states that are a hazard to navigation. Recent advances in the understanding and modeling capability of ocean currents at scales of 10 km or less have revealed the ubiquitous presence of fronts and filaments. Based on realistic numerical models, we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km, including important variations at 10 km. This current-induced variability creates gradients in wave heights that were previously overlooked and are relevant for extreme wave heights and remote sensing. The spectrum of significant wave heights is found to be of the order of 70⟨Hs ⟩2/(g2⟨Tm0,-1⟩2) times the current spectrum, where ⟨Hs ⟩ is the spatially-averaged significant wave height, ⟨Tm0,-1⟩ is the average energy period, and g is the gravity acceleration. This small scale variability is consistent with Jason-3 and SARAL along-track variability. We will discuss how future satellite mission with wave spectrometers can help observe these wave-current interactions. CFOSAT is due for launch in 2018, and SKIM is a proposal for ESA Earth Explorer 9.

Parametric instability and wave turbulence driven by tidal excitation of internal waves

NASA Astrophysics Data System (ADS)

Le Reun, Thomas; Favier, Benjamin; Le Bars, Michael

2018-04-01

We investigate the stability of stratified fluid layers undergoing homogeneous and periodic tidal deformation. We first introduce a local model which allows to study velocity and buoyancy fluctuations in a Lagrangian domain periodically stretched and sheared by the tidal base flow. While keeping the key physical ingredients only, such a model is efficient to simulate planetary regimes where tidal amplitudes and dissipation are small. With this model, we prove that tidal flows are able to drive parametric subharmonic resonances of internal waves, in a way reminiscent of the elliptical instability in rotating fluids. The growth rates computed via Direct Numerical Simulations (DNS) are in very good agreement with WKB analysis and Floquet theory. We also investigate the turbulence driven by this instability mechanism. With spatio-temporal analysis, we show that it is a weak internal wave turbulence occurring at small Froude and buoyancy Reynolds numbers. When the gap between the excitation and the Brunt-V\\"ais\\"al\\"a frequencies is increased, the frequency spectrum of this wave turbulence displays a -2 power law reminiscent of the high-frequency branch of the Garett and Munk spectrum (Garrett & Munk 1979) which has been measured in the oceans. In addition, we find that the mixing efficiency is altered compared to what is computed in the context of DNS of stratified turbulence excited at small Froude and large buoyancy Reynolds numbers and is consistent with a superposition of waves.

A comparative study of the mechanisms of migrating diurnal tidal variability due to interaction with propagating planetary waves

NASA Astrophysics Data System (ADS)

Chang, Loren; Palo, Scott; Liu, Hanli

The migrating diurnal tide is one of the dominant dynamical features of the Earth's Mesosphere and Lower Thermosphere (MLT) region, particularly at low latitudes. As an actively forced disturbance with a period of 24 hours and westward zonal wave number 1, the migrating diurnal tide represents the atmospheric response to the largest component of solar forcing, propagating upwards from excitation regions in the lower atmosphere. While the seasonal evolution of the migrating diurnal tide has been well explored, ground-based observations of the tide have exhibited a modulation of tidal amplitudes at periods related to those of propagating planetary waves generally present in the region, as well as a decrease in tidal amplitudes during large planetary wave events. Past studies have attributed tidal amplitude modulation to the presence of child waves generated as a byproduct of nonlinear wave-tide interactions. The resulting child waves have frequencies and wavenumbers that are the sum and difference of those of the parent waves. Many questions still remain about the nature and physical drivers responsible for such interactions. The conditions under which various planetary waves may or may not interact with the atmospheric tides, the overall effect on the tidal response, as well as the physical mechanisms coupling the planetary wave and the tide interaction, which has not clearly been determined. These questions are addressed in a recent modeling study, by examining two general categories of planetary waves that are known to attain significant amplitudes in the low latitude and equa-torial region where the migrating diurnal tide is dominant. These are the eastward propagating class of ultra fast Kelvin (UFK) waves with periods near three days which attain their largest amplitudes in the temperature and zonal wind fields of the equatorial lower thermosphere. The second wave examined is the quasi-two day wave (QTDW) which is a westward propagating Rossby wave and can amplify raplidly due to a nonlinear interaction with the mean flow and attain large amplitudes in both components of the wind field and the temperature field in the summer hemisphere over a period of a few days during post-solstice periods. The NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) and Whole Atmosphere Community Climate Model (WACCM) are both state of the art general circulation models and are utilized to simulate the aforementioned planetary waves. The goal of this study is to identify specific changes in the structure of the migrat-ing diurnal tide due to interaction with these planetary waves and to understand the driving processes. The physical mechanisms that serve to couple the tide and the planetary waves are identified through analysis of the tidal momentum tendencies, the background atmosphere, as well as changes in tidal propagation. Results showing the impact of these planetary waves on the structure and evolution of the migrating diurnal tide will be presented.

Understanding processes controlling sediment transports at the mouth of a highly energetic inlet system (San Francisco Bay, CA)

USGS Publications Warehouse

Elias, Edwin P.L.; Hansen, Jeff E.; Barnard, P.L.; Jaffee, B.E.; Schoellhamer, D.H.

2013-01-01

San Francisco Bay is one of the largest estuaries along the U.S. West Coast and is linked to the Pacific Ocean through the Golden Gate, a 100 m deep bedrock inlet. A coupled wave, flow and sediment transport model is used to quantify the sediment linkages between San Francisco Bay, the Golden Gate, and the adjacent open coast. Flow and sediment transport processes are investigated using an ensemble average of 24 climatologically derived wave cases and a 24.8 h representative tidal cycle. The model simulations show that within the inlet, flow and sediment transport is tidally dominated and driven by asymmetry of the ebb and flood tides. Peak ebb velocities exceed the peak flood velocities in the narrow Golden Gate channel as a result of flow convergence and acceleration. Persistent flow and sediment gyres at the headland tips are formed that limit sediment transfer from the ebb-tidal delta to the inlet and into the bay. The residual transport pattern in the inlet is dominated by a lateral segregation with a large ebb-dominant sediment transport (and flow) prevailing along the deeper north side of the Golden Gate channel, and smaller flood dominant transports along the shallow southern margin. The seaward edge of the ebb-tidal delta largely corresponds to the seaward extent of strong tidal flows. On the ebb-tidal delta, both waves and tidal forcing govern flow and sediment transport. Wave focusing by the ebb-tidal delta leads to strong patterns of sediment convergence and divergence along the adjacent Ocean Beach.

Beach Cusps: Spatial distribution and time evolution at Massaguaçú beach (SP), Brazil

NASA Astrophysics Data System (ADS)

dos Santos, H. H.; Siegle, E.; Sousa, P. H.

2013-05-01

Beach cusps are crescentic morphological structures observed on the foreshore of beaches characterized by steep seaward protruding extensions, called cusp horns, and gently sloped landward extensions, called cusp embayments. Their formation depends on the grain size, beach slope, tidal range and incoming waves. Cusps are best developed on gravel or shingle beaches, small tidal range with a large slope for incoming waves generate a well-developed swash excursion. These structures are quickly responding to wave climate and tidal range, changing the position of the rhythmic features on the beach face. Beach cusps are favored by normal incoming waves, while oblique waves tend to wash these features out. This study aims to analyze the spatial distribution and temporal evolution of rhythmic features such as beach cusps in Massaguaçú embayment (Caraguatatuba, northern coast of São Paulo, Brazil). This embayment has an extension of 7.5 km with reflective beaches cusped mainly in its more exposed central portion. The data set for this study consists of a series of video images (Argus system), covering a stretch of the beach. Visible beach cusps were digitalized from these rectified images. Results obtained from the images were related to the wave climate, water level and the storm surges. Results show that the cusps on the upper portion of the foreshore were more regular and present than the cusps on the lower portion of the foreshore due to the tidal modulation of wave action. The cusp spacing on the upper portion of the foreshore is of about 38 m and the lower portion of the foreshore is of about 28 m and their presence was correlated with the wave direction and water elevation. As expected, waves approaching with shore-normal angles (southeast direction) were favorable to the formation of beach cusps while the waves from the southwest, south, east and northeast generated a longshore current that reduced or destroyed any rhythmic feature. Other important forcing was the influence of the water level. Waves acting at higher water levels are able to produce the less dynamic upper layer of cusps. During 31 consecutive days from 8 July 2011 to 8 August of the same year these features show four periods with the presence of cusps on the upper and lower portion of the foreshore with three periods with cups only on the upper portion of the foreshore. The analyzed dataset shows the highly dynamic behavior of cusps, with rapid generation and destruction, related directly to its forcing hydrodynamic conditions.

7 CFR 1945.6 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-01-01

..., tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption... hurricane, tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic..., earthquake, hurricane or tornado. (B) A single storm, or series of storms, accompanied by severe hail...

7 CFR 1945.6 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-01-01

..., tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption... hurricane, tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic..., earthquake, hurricane or tornado. (B) A single storm, or series of storms, accompanied by severe hail...

7 CFR 1945.6 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-01-01

..., tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic eruption... hurricane, tornado, storm, flood, high water, wind-driven water, tidal wave, tsunami, earthquake, volcanic..., earthquake, hurricane or tornado. (B) A single storm, or series of storms, accompanied by severe hail...

Critical width of tidal flats triggers marsh collapse in the absence of sea-level rise

PubMed Central

Mariotti, Giulio; Fagherazzi, Sergio

2013-01-01

High rates of wave-induced erosion along salt marsh boundaries challenge the idea that marsh survival is dictated by the competition between vertical sediment accretion and relative sea-level rise. Because waves pounding marshes are often locally generated in enclosed basins, the depth and width of surrounding tidal flats have a pivoting control on marsh erosion. Here, we show the existence of a threshold width for tidal flats bordering salt marshes. Once this threshold is exceeded, irreversible marsh erosion takes place even in the absence of sea-level rise. This catastrophic collapse occurs because of the positive feedbacks among tidal flat widening by wave-induced marsh erosion, tidal flat deepening driven by wave bed shear stress, and local wind wave generation. The threshold width is determined by analyzing the 50-y evolution of 54 marsh basins along the US Atlantic Coast. The presence of a critical basin width is predicted by a dynamic model that accounts for both horizontal marsh migration and vertical adjustment of marshes and tidal flats. Variability in sediment supply, rather than in relative sea-level rise or wind regime, explains the different critical width, and hence erosion vulnerability, found at different sites. We conclude that sediment starvation of coastlines produced by river dredging and damming is a major anthropogenic driver of marsh loss at the study sites and generates effects at least comparable to the accelerating sea-level rise due to global warming. PMID:23513219

Critical width of tidal flats triggers marsh collapse in the absence of sea-level rise.

PubMed

Mariotti, Giulio; Fagherazzi, Sergio

2013-04-02

High rates of wave-induced erosion along salt marsh boundaries challenge the idea that marsh survival is dictated by the competition between vertical sediment accretion and relative sea-level rise. Because waves pounding marshes are often locally generated in enclosed basins, the depth and width of surrounding tidal flats have a pivoting control on marsh erosion. Here, we show the existence of a threshold width for tidal flats bordering salt marshes. Once this threshold is exceeded, irreversible marsh erosion takes place even in the absence of sea-level rise. This catastrophic collapse occurs because of the positive feedbacks among tidal flat widening by wave-induced marsh erosion, tidal flat deepening driven by wave bed shear stress, and local wind wave generation. The threshold width is determined by analyzing the 50-y evolution of 54 marsh basins along the US Atlantic Coast. The presence of a critical basin width is predicted by a dynamic model that accounts for both horizontal marsh migration and vertical adjustment of marshes and tidal flats. Variability in sediment supply, rather than in relative sea-level rise or wind regime, explains the different critical width, and hence erosion vulnerability, found at different sites. We conclude that sediment starvation of coastlines produced by river dredging and damming is a major anthropogenic driver of marsh loss at the study sites and generates effects at least comparable to the accelerating sea-level rise due to global warming.

Equatorial Plasma Bubbles: Effect of Thermospheric Winds Modulated by DE3 Tidal Waves

NASA Astrophysics Data System (ADS)

Sidorova, L. N.; Filippov, S. V.

2018-03-01

A hypothesis about the effect of the tropospheric source on the longitudinal distributions of the equatorial plasma bubbles observed in the topside ionosphere was proposed earlier. It was supposed that this influence is transferred mainly by the thermospheric winds modulated by the DE3 tropospheric tidal waves. This conclusion was based on the discovered high degree correlation ( R ≅ 0.79) between the variations of the longitudinal distribution of the plasma bubbles and the neutral atmospheric density. In this work, the hypothesis of the effect of the thermospheric tidal waves on the plasma bubbles at the stage of their generation is subjected to further verification. With this purpose, the longitudinal distributions of the frequency of the plasma bubble observations at the different ionospheric altitudes ( 600 km, ROCSAT-1; 1100 km, ISS-b) are analyzed; their principal similarity is revealed. Comparative analysis of these distributions with the longitudinal profile of the deviations of the zonal thermospheric wind ( 400 km, CHAMP) modulated by the DE3 tidal wave is carried out; their considerable correlation ( R ≅ 0.69) is revealed. We conclude that the longitudinal variations of the zonal wind associated with DE3 tidal waves can effect the longitudinal variations in the appearance frequency of the initial "seeding" perturbations, which further evolve into the plasma bubbles.

Wave and Current Measurements From the Coastal Storms Program (CSP) Buoy 41012 off St. Augustine, FL

NASA Astrophysics Data System (ADS)

Crout, R. L.

2008-05-01

The Coastal Storms Program (CSP) is a NOAA program that involves several different branches within NOAA. Components of the National Ocean Service, the National Weather Service, the National Marine Fisheries Service, and the Office of Oceanic and Atmospheric Research participate in CSP, which is administered by the Coastal Services Center. CSP selects an area where an impact in support of the NOAA Societal Goals can be made. The first area selected was the northeast coast of Florida in 2002. In addition to coastal water level stations and modeling efforts, a 3-meter discuss buoy (WMO 41012) was deployed off the coast of St. Augustine, FL in approximately 38 meters of water. In addition to the normal complement of meteorological sensors, Buoy 41012 contained a sensor to measure directional waves at hourly intervals, a temperature-conductivity sensor to measure near-surface temperature and salinity, and a current profiler to obtain near-surface to near-bottom currents at hourly intervals. These data on the continental shelf provide a view of the oceanography on the inner margin of the Gulf Stream. The data are served over the National Data Buoy Center's web page and over the Global Telecommunications System. The waves and currents during the period from September 2005 through December 2007 are related to coastal storms, hurricanes, tides, and Gulf Stream intrusions. During several late fall and winter periods the waves exceeded 4.5 meters. The on-offshore component of the currents appears to be tidally driven, however, predominant on- and off-shore flows are observed in response to storms and Gulf Stream intrusions. The primary component of the flow is aligned alongshore and although the tidal influence is obvious, extended periods of northward and southward currents are observed. Currents approaching 2 knots are observed at various times during the period that the buoy has been active. The high currents appear to be in response to strong wind events (atmospheric frontal passages) and Gulf Stream intrusions.

Characteristics of inertial currents observed in offshore wave records

NASA Astrophysics Data System (ADS)

Gemmrich, J.; Garrett, C.

2012-04-01

It is well known that ambient currents can change the amplitude, direction and frequency of ocean surface waves. Regions with persistent strong currents, such as the Agulhas current off the east coast of South Africa, are known as areas of extreme waves, and wave height modulations of up to 50% observed in the shallow North Sea have been linked to tidal currents. In the open ocean, inertial currents, while intermittent, are typically the most energetic currents with speeds up to 0.5 m/s, and can interact with the surface wave field to create wave modulation, though this has not previously been reported. We use long records of significant wave heights from buoy observations in the northeast Pacific and show evidence of significant modulation at frequencies that are slightly higher than the local inertial frequency. Quite apart from the relevance to surface waves, this result can provide a consistent and independent measurement, over a wide range of latitudes, of the frequency blue-shift, the strength and intermittency of ocean surface inertial currents. Near-inertial waves constitute the most energetic portion of the internal wave band and play a significant role in deep ocean mixing. So far, observational data on near-surface inertial currents has tended to come from short records that do not permit the reliable determination of the frequency blue-shift, though this is an important factor affecting the energy flux from the surface into deeper waters. Long records from routine wave height observations are widely available and could help to shed new light globally on the blue-shift and on the characteristics of inertial currents.

Feasibility of a Novel Optoacoustic Device to Precisely Localize Endotracheal Tube Positioning in a Cadaver Model

DTIC Science & Technology

2016-11-02

million per year to U.S. hospitals [1,2]. Current methods of assessing ETT position include chest radiography, end- tidal carbon dioxide (EtCO2...lasers to generate sound waves to determine the position of “labeled” ETTs within millimeters of accuracy. Laser optoacoustic imaging combines the merits...of optical tomography (high optical contrast) and ultrasound imaging (minimal scattering of acoustic waves ) to yield high contrast, sensitivity, and

Internal tidal currents in the Gaoping (Kaoping) Submarine Canyon

USGS Publications Warehouse

Lee, I.-H.; Wang, Y.-H.; Liu, J.T.; Chuang, W.-S.; Xu, Jie

2009-01-01

Data from five separate field experiments during 2000-2006 were used to study the internal tidal flow patterns in the Gaoping (formerly spelled Kaoping) Submarine Canyon. The internal tides are large with maximum interface displacements of about 200??m and maximum velocities of over 100cm/s. They are characterized by a first-mode velocity and density structure with zero crossing at about 100??m depth. In the lower layer, the currents increase with increasing depth. The density interface and the along-channel velocity are approximately 90?? out-of-phase, suggesting a predominant standing wave pattern. However, partial reflection is indicated as there is a consistent phase advance between sea level and density interface along the canyon axis. ?? 2008 Elsevier B.V. All rights reserved.

Transport of pollutants and sediment in the area of the Wave Hub (Celtic Sea)

NASA Astrophysics Data System (ADS)

Shapiro, Georgy; Huntley, David

2010-05-01

Ocean waves are a sustainable source of alternative energy that, if properly developed, will provide a quarter of current electricity demand and contribute to lowering the UK's reliance on fossil fuels. The UK government has given planning approval for a pilot power plant called the Wave Hub located in the eastern Celtic Sea off the Cornish north coast. The impact of a small number of devices on the physical environment is expected to be subtle outside the exclusion zone. However, such pilot projects are considered as the launching pad in the UK's ambitious programme to create a new wave energy industry. Large scale off-shore industrial activity can interact with the physical environment of the shelf sea in a two-fold manner: (i) the wave farm is affected by the waves, currents, variation in temperature and movements of sediment, and (ii) it can impact on the marine environment via a number of ways including release of dissolved and suspended matter during construction, operational and decommission stages of the project. These changes in the physical environment can then be translated into changes of the ecosystem and corresponding human activities. The Celtic Sea has a highly variable and complex thermal structure. In the spring and summer the water column becomes stratified due to solar heating of the surface layer, particularly in the areas of greater depth and/or low currents, where the turbulence is insufficient to mix the entire water column. Fronts form at the junctions of stratified and mixed water columns and these fronts generate currents which flow along the fronts. These frontal currents are subject to baroclinic instability and generate a whole set of mesoscale (i.e. comparable with the baroclinic Rossby radius) features such as eddies, filaments and mushroom currents, which are clearly seen on satellite images. Ecosystems are particularly concentrated in the vicinity of fronts so changes in frontal strength or location can have significant biological consequences. This paper presents some preliminary modelling results of a baseline study focussed on hind-cast and now-cast simulation of the 3D structure of temperature, salinity and current velocity in the area immediately adjacent to the location of the Wave Hub. Of the range of available 3D numerical models for shelf sea hydrodynamics, we have selected the Proudman Oceanographic Laboratory Coastal Modelling System (POLCOMS). The POLCOMS has successfully been used in a number of coastal/shelf sea regions to simulate circulation of coastal waters. Modelling is carried out in the region of approximately 200x 200 km with the variable vertical resolution typically less than 2 m. Such parameters allow resololution of the formation of coastal density fronts both within and outside the wave shadow zone, expected to be of the order of tens of kilometres. The meteorological parameters are obtained from the publicly available NCEP re-analyses data base. These parameters include components of the wind velocity and the surface heat fluxes, air pressure at sea level; temperature and humidity in the low troposphere; precipitation and cloudiness. In this study, the transport of pollution is simulated by a number of passive drifters located at a certain depth at a number of locations including the central point of the Wave Hub. Sediment transport is modelled using the Engelund-Hansen algorithm taking the current velocities produced by the POLCOMS as an input parameter. The Celtic sea is a tidally dominated region, and the modelling is run both in full-forcing and in tide-only modes in order to assess effects of density fronts on the residual (tidally averaged) circulation pattern. The results show that the pollution pathways are very sensitive to the formation of temperature fronts. In some cases the passive traces move in nearly opposite directions when the effect of temperature fronts is disregarded. Sediment transport is highly non-uniform spatially with some four areas along the Cornish coast being particularly affected. Sediment transport is also sensitive to the neap-spring phase of the tidal cycle. Residual currents caused by the non-linear tidal stream rectification are comparable or slower (depending on location) than the density driven currents caused by formation of temperature fronts. Location of the Wave Hub is particularly prone to strong transport of suspended particulate matter subject to availability of sediment on the seabed. These preliminary results suggest that the region of the Celtic Sea where the proposed Wave Hub is sited is an excellent location for assessing potential impacts of wave energy extraction. The authors wish to thank D. L. Aleynik for his help in setting up the POLCOMS model and the PRIMaRE project for providing computing facilities.

Tidal Channel Dynamics and Muddy Substrates: A Comparison between a Wave Dominated and a Tidal Dominated System

DTIC Science & Technology

2012-09-30

standard linear wave theory. Suspended sediment concentration (SSC) was estimated using the backscatter signal of the ADCP and the turbidity value...measured by the OBS when present. The OBS turbidity signal was calibrated against SSC measured in a laboratory tank, using sediments collected on the...link the geotechnical properties of sediment substrates to the spatial and hydrodynamic characteristics of tidal channels • To develop new

Critical bifurcation of shallow microtidal landforms in tidal flats and salt marshes

PubMed Central

Fagherazzi, Sergio; Carniello, Luca; D'Alpaos, Luigi; Defina, Andrea

2006-01-01

Shallow tidal basins are characterized by extensive tidal flats and salt marshes that lie within specific ranges of elevation, whereas intermediate elevations are less frequent in intertidal landscapes. Here we show that this bimodal distribution of elevations stems from the characteristics of wave-induced sediment resuspension and, in particular, from the reduction of maximum wave height caused by dissipative processes in shallow waters. The conceptual model presented herein is applied to the Venice Lagoon, Italy, and demonstrates that areas at intermediate elevations are inherently unstable and tend to become either tidal flats or salt marshes. PMID:16707583

Wave- and tidally-driven flow and sediment flux across a fringing coral reef: Southern Molokai, Hawaii

USGS Publications Warehouse

Storlazzi, C.D.; Ogston, A.S.; Bothner, Michael H.; Field, M.E.; Presto, M.K.

2004-01-01

The fringing coral reef off the south coast of Molokai, Hawaii is currently being studied as part of a US Geological Survey (USGS) multi-disciplinary project that focuses on geologic and oceanographic processes that affect coral reef systems. For this investigation, four instrument packages were deployed across the fringing coral reef during the summer of 2001 to understand the processes governing fine-grained terrestrial sediment suspension on the shallow reef flat (h=1m) and its advection across the reef crest and onto the deeper fore reef. The time-series measurements suggest the following conceptual model of water and fine-grained sediment transport across the reef: Relatively cool, clear water flows up onto the reef flat during flooding tides. At high tide, more deep-water wave energy is able to propagate onto the reef flat and larger Trade wind-driven waves can develop on the reef flat, thereby increasing sediment suspension. Trade wind-driven surface currents and wave breaking at the reef crest cause setup of water on the reef flat, further increasing the water depth and enhancing the development of depth-limited waves and sediment suspension. As the tide ebbs, the water and associated suspended sediment on the reef flat drains off the reef flat and is advected offshore and to the west by Trade wind- and tidally- driven currents. Observations on the fore reef show relatively high turbidity throughout the water column during the ebb tide. It therefore appears that high suspended sediment concentrations on the deeper fore reef, where active coral growth is at a maximum, are dynamically linked to processes on the muddy, shallow reef flat.

Can salt marshes survive sea level rise ?

NASA Astrophysics Data System (ADS)

Tambroni, N.; Seminara, G.

2008-12-01

Stability of salt marshes is a very delicate issue depending on the subtle interplay among hydrodynamics, morphodynamics and ecology. In fact, the elevation of the marsh platform depends essentially on three effects: i) the production of soil associated with sediments resuspended by tidal currents and wind waves in the adjacent tidal flats, advected to the marsh and settling therein; ii) production of organic sediments by the salt marsh vegetation; iii) soil 'loss' driven by sea level rise and subsidence. In order to gain insight into the mechanics of the process, we consider a schematic configuration consisting of a salt marsh located at the landward end of a tidal channel connected at the upstream end with a tidal sea, under different scenarios of sea level rise. We extend the simple 1D model for the morphodynamic evolution of a tidal channel formulated by Lanzoni and Seminara (2002, Journal of Geophysical Research-Oceans, 107, C1) allowing for sediment resuspension in the channel and vegetation growth in the marsh using the depth dependent model of biomass productivity of Spartina proposed by Morris et al. (2002, Ecology, 83, pp. 2869 - 2877). We first focus on the case of a tide dominated salt marsh neglecting wind driven sediment resuspension in the shoal. Results show that the production of biomass plays a crucial role on salt marsh stability and, provided productivity is high enough, it may turn out to be sufficient to counteract the effects of sea level rise even in the absence of significant supply of mineral sediments. The additional effect of wind resuspension is then introduced. Note that the wind action is twofold: on one hand, it generates wind waves the amplitude of which is strongly dependent on shoal depth and wind fetch; on the other hand, it generates currents driven by the surface setup induced by the shear stress acting on the free surface. Here, each contribution is analysed separately. Results show that the values of bottom stress induced by wind setup are small compared with those associated with wind waves. However, the permanence of wind currents makes them as significant as the oscillating tidal currents in determining the direction and the intensity of the residual sediment flux. Marshes are typically characterised by a variety of vegetation species competing for habitat space within the intertidal zone: we analyze this feature by considering the case of two different species. Preliminary results show that the presence of a species characterised by a narrower habitat range, lower optimum elevation and biomass productivity, has a positive feedback on the growth of the other species. Moreover, the presence of an invader raises marsh elevation above the value reached in the presence of just one species. Finally, we investigate the effect of a reduction of the amount of sediments supplied from the sea.

Sea state indices for a coastal strait

NASA Astrophysics Data System (ADS)

Gemmrich, Johannes; Dewey, Richard

2017-04-01

The Strait of Georgia at the west coast of Canada is an enclosed coastal strait, about 250km long and 25 to 50 km wide, with great socio-economic importance. Regular freighter traffic, ferry services, commercial and sport fisheries, and recreational boating, makes the area one of the busiest marine areas in the world. Waves in SoG are generally small, with the median value of the significant wave height Hs=0.3m. However, strong outflows off the mountainous terrain can generate significant wave heights Hs > 2.5m, with high spatial and temporal variability. In addition, strong tidal currents and the Fraser River outflow generate localized regions of steep and breaking waves that are of particular concern. We have implemented the Wavewatch III model at 500m-resolution, forced by Environment Canada's high resolution atmospheric model winds and currents from the UBC NEMO implementation of the Salish Sea. The final output combines GIS layers of the predicted wave field (Hs, dominant wave length and direction), the modeled wind field and currents, observed currents from a set of CODAR systems, and a sea state index that highlights regions of potentially steep and dangerous waves.

Waves: Internal Tides

NASA Technical Reports Server (NTRS)

Ray, Richard D.

1999-01-01

Oceanic internal tides are internal waves with tidal periodicities. They are ubiquitous throughout the ocean, although generally more pronounced near large bathymetric features such as mid-ocean ridges and continental slopes. The internal vertical displacements associated with these waves can be extraordinarily large. Near some shelf breaks where the surface tides are strong, internal displacements (e.g., of an isothermal surface) can exceed 200 meters. Displacements of 10 meters in the open ocean are not uncommon. The associated current velocities are usually comparable to or larger than the currents of the surface tide. On continental shelves internal tides can occasionally generate packets of internal solitons, which are detectable in remote sensing imagery. Other common nonlinear features are generation of higher harmonics (e.g., 6-hr waves) and wave breaking. Internal tides are known to be an important energy source for mixing of shelf waters. Recent research suggests that they may also be a significant energy source for deep-ocean mixing.

The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China

NASA Astrophysics Data System (ADS)

Zhang, Min; Townend, Ian; Cai, Huayang; He, Jiawei; Mei, Xuefei

2018-02-01

The geomorphology of the Yangtze Estuary in the Changjiang River Delta in Eastern China has been the subject of extensive research. This study extends previous work to examine the influence of wind-waves on the mouth-bar, where about half of the river-borne material settles to the bed. The site is located just outside of Changjiang River mouth, which is meso-tidal and subject to seasonally varying river flows and wind-wave conditions. Modeling was performed with a coupled wave-current hydrodynamic model using TELEMAC and TOMAWAC and validated against observed data. Bottom Shear Stress (BSS) from river, tide and waves based on the numerical model output was used to infer the respective contribution to the evolution of the subaqueous delta. Our examination did not however extend to modeling the sediment transport or the morphological bed changes. The results suggest that (i) the dominance of river discharge is limited to an area inside the mouth, while outside, the mouth-bar is tide-wave dominant; (ii) considering just the tide, the currents on the shallow shoals are flood dominant and deep channels are ebb dominant, which induces continued accretion over the shallows and erodes the deeper parts of the mouth-bar until the tidal currents become too weak to transport sediment; (iii) whereas waves are very efficient at reshaping the shallow shoals, with the effect being subtly dependent on the depth distribution over the mouth-bar; (iv) the stability of shallow shoal morphology is highly dependent on the presence of seasonal wind-waves and characterized as "summer storing and winter erosion", while deep channels perform like corridors of water and sediment, exporting sediment all year round. The nature of the mouth-bar response has important implications for coastal management, such as the ongoing deep water channel maintenance, reclamations and coastal defense measures.

Tidal waves within the thermosphere. [emphasizing wave dissipation and diffusion

NASA Technical Reports Server (NTRS)

Volland, H.; Mayr, H. G.

1974-01-01

The eigenfunctions of the atmosphere (the Hough functions within the lower atmosphere below about 100 km) change their structure and their propagation characteristics within the thermosphere due to dissipation effects such as heat conduction, viscosity, and ion drag. Wave dissipation can be parameterized to a first-order approximation by a complex frequency, the imaginary term of which simulates an effective ion drag force. It is shown how the equivalent depth, the attenuation, and the vertical wavelength of the predominant symmetric diurnal tidal modes change with height as functions of effective ion drag. The boundary conditions of tidal waves are discussed, and asymptotic solutions for the wave parameters like pressure, density, temperature, and wind generated by a heat input proportional to the mean pressure are given. Finally, diffusion effects upon the minor constituents within the thermosphere are described.

Tidal energetics: Studies with a barotropic model

NASA Astrophysics Data System (ADS)

Stewart, James Scott

The tidal energy from luni-solar gravitational forcing is dissipated principally through the dissipation of oceanic tides. Recent estimates using disparate methods, including analysis of satellite orbits and the timing of ancient eclipses, now indicate that this dissipation totals approximately 3.5 terawatts. However, the mechanisms and spatial distribution of this dissipation is not yet fully understood. In this work, three different aspects of tidal energetics are investigated with a variable resolution barotropic tidal model. The distribution of tidal energy, dissipation and energy flux are examined using high resolution models of several marginal seas: the European shelf, the Sea of Okhotsk, the Yellow and East China Seas, the South China Sea and the Bering Sea. Most modern tide models dissipate tidal energy with a quadratic friction parameterization of bottom friction. Since such dissipation depends nonlinearly on the velocity of the tidal current, these models dissipate primarily in shallow seas where current magnitudes are high. Without assimilating observational data, such tidal models have unreasonably high levels of tidal-period averaged kinetic and potential energies. I have added a linear friction parameterization to the traditional quadratic formulation and am able to obtain realistic tidal energy levels with an unassimilated model. The resulting model is used to investigate the tidal energetics of the recent geological past when sea level was 50 meters higher and 120 meters lower than at the present time. Long-period tides are of small enough amplitude that their energetics are an almost negligible part of the total tidal energy budget. However, the behavior of these tides yields insights into the response of the ocean to large scale forcing. We have modeled the lunar fortnightly (M f) and lunar monthly (Mm) tidal components and determined that the ratio of the Mf potential-to-kinetic energy ratio to that of Mm is about 3.9, consistent with values expected for long Rossby wave dynamics. Also, we obtain quality (Q) values for the Mf and Mm tides of 5.9 and 6.2 respectively which is consistent with recent inferences of basin circulation responses of Q of about 5.5 for 5-day synoptic forcing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piro, Anthony L., E-mail: piro@caltech.edu

The recently discovered system J0651 is the tightest known detached white dwarf (WD) binary. Since it has not yet initiated Roche-lobe overflow, it provides a relatively clean environment for testing our understanding of tidal interactions. I investigate the tidal heating of each WD, parameterized in terms of its tidal Q parameter. Assuming that the heating can be radiated efficiently, the current luminosities are consistent with Q {sub 1} {approx} 7 x 10{sup 10} and Q {sub 2} {approx} 2 x 10{sup 7}, for the He and C/O WDs, respectively. Conversely, if the observed luminosities are merely from the cooling ofmore » the WDs, these estimated values of Q represent the upper limits. A large Q {sub 1} for the He WD means its spin velocity will be slower than that expected if it was tidally locked, which, since the binary is eclipsing, may be measurable via the Rossiter-McLaughlin effect. After one year, gravitational wave emission shifts the time of eclipses by 5.5 s, but tidal interactions cause the orbit to shrink more rapidly, changing the time by up to an additional 0.3 s after a year. Future eclipse timing measurements may therefore infer the degree of tidal locking.« less

Wave Shape and Impact Pressure Measurements at a Rock Coast Cliff

NASA Astrophysics Data System (ADS)

Varley, S. J.; Rosser, N. J.; Brain, M.; Vann Jones, E. C.

2016-02-01

Rock coast research focuses largely on wave behaviour across beaches and shore platforms but rarely considers direct wave interaction with cliffs. Hydraulic action is one of the most important drivers of erosion along rock coasts. The magnitude of wave impact pressure has been shown by numerical and laboratory studies to be related to the wave shape. In deep water, a structure is only subjected to the hydrostatic pressure due to the oscillating clapotis. Dynamic pressures, related to the wave celerity, are exerted in shallower water when the wave is breaking at the point of impact; very high magnitude, short duration shock pressures are theorised to occur when the approaching wavefront is vertical. As such, wave shape may directly influence the potential of the impact to weaken rock and cause erosion. Measurements of impact pressure at coastal cliffs are limited, and the occurrence and influence of this phenomenon is currently poorly constrained. To address this, we have undertaken a field monitoring study on the magnitude and vertical distribution of wave impact pressures at the rocky, macro-tidal coastline of Staithes, North Yorkshire, UK. A series of piezo-resistive pressure transducers and a camera were installed at the base of the cliff during low tide. Transducers were deployed vertically up the cliff face and aligned shore-normal to capture the variation in static and dynamic pressure with height during a full spring tidal cycle. Five minute bursts of 5 kHz pressure readings and 4 Hz wave imaging were sampled every 30 minutes for six hours during high tide. Pressure measurements were then compensated for temperature and combined with wave imaging to produce a pressure time series and qualitative wave shape category for each wave impact. Results indicate the presence of a non-linear relationship between pressure impact magnitude, the occurrence of shock pressures, wave shape and tidal stage, and suggest that breaker type on impact (and controls thereof) may be fundamental in dictating the effectiveness of hydraulic action in eroding rock coast cliffs. Our findings demonstrate the sensitivity of wave loading to changes in water depth and, hence, projected sea-level rise. This research leads directly into a wider project investigating the role of wave shape as a key control on marine forcing of erosion.

Characteristics of wind waves in shallow tidal basins and how they affect bed shear stress, bottom erosion, and the morphodynamic evolution of coupled marsh and mudflat landforms

NASA Astrophysics Data System (ADS)

Tommasini, Laura; Carniello, Luca; Goodwin, Guillaume; Mudd, Simon M.; Matticchio, Bruno; D'Alpaos, Andrea

2017-04-01

Wind-wave induced erosion is one of the main processes controlling the morphodynamic evolution of shallow tidal basins, because wind waves promote the erosion of subtidal platforms, tidal flats and salt marshes. Our study considered zero-, one-and two-dimensional wave models. First, we analyzed the relations between wave parameters, depth and bed shear stress with constant and variable wave period considering two zero-dimensional models based on the Young and Verhagen (1996), and Carniello et al. (2005, 2011) approaches. The first one is an empirical method that computes wave height and the variable wave period from wind velocity, fetch and water depth. The second one is based on the solution of wave action conservation equation, we use this second approach for computing the bottom shear stress and wave height, considering variable and constant (t=2s) wave period. Second, we compared the wave spectral model SWAN with a fully coupled Wind-Wave Tidal Model applied to a 1D rectangular domain. These models describe both the growth and propagation of wind waves. Finally, we applied the two-dimensional Wind Wave Tidal Model (WWTM) to six different configurations of the Venice lagoon considering the same boundary conditions and we evaluated the spatial variation of mean wave power density. The analysis with zero-dimensional models show that the effects of the different model assumptions on the wave period and on the wave height computation cannot be neglected. In particular, the relationships between bottom shear stress and water depth have different shapes. Two results emerge: first, the differences are higher for small depths, and then the maximum values reached with the Young and Verhagen (1996) approach are greater than the maximum values obtained with WWTM approach. The results obtained with two-dimensional models suggest that the wave height is different in particular for small fetch, this could be due to the different formulation of the wave period. Finally, the application of WWTM for the entire Lagoon basin underlines an increase of the mean power density in the last four centuries, in particular in the central-southern part of the lagoon between Chioggia and Malamocco inlets.

Tsunami Wave Run-up on a Vertical Wall in Tidal Environment

NASA Astrophysics Data System (ADS)

Didenkulova, Ira; Pelinovsky, Efim

2018-04-01

We solve analytically a nonlinear problem of shallow water theory for the tsunami wave run-up on a vertical wall in tidal environment. Shown that the tide can be considered static in the process of tsunami wave run-up. In this approximation, it is possible to obtain the exact solution for the run-up height as a function of the incident wave height. This allows us to investigate the tide influence on the run-up characteristics.

Large submarine sand waves and gravel lag substrates on Georges Bank off Atlantic Canada

USGS Publications Warehouse

Todd, B.J.; Valentine, Page C.; Harris, Peter T; Baker, E.K.

2012-01-01

Georges Bank is a large, shallow, continental shelf feature offshore of New England and Atlantic Canada. The bank is mantled with a veneer of glacial debris transported during the late Pleistocene from continental areas lying to the north. These sediments were reworked by marine processes during postglacial sea-level transgression and continue to be modified by the modern oceanic regime. The surficial geology of the Canadian portion of the bank is a widespread gravel lag overlain in places by well sorted sand occurring as bedforms. The most widespread bedforms are large, mobile, asymmetrical sand waves up to 19 m in height formed through sediment transport by strong tidal-driven and possibly storm-driven currents. Well-defined curvilinear bedform crests up to 15 km long form a complex bifurcating pattern having an overall southwest–northeast strike, which is normal to the direction of the major axis of the semidiurnal tidal current ellipse. Minor fields of immobile, symmetrical sand waves are situated in bathymetric lows. Rare mobile, asymmetrical barchan dunes are lying on the gravel lag in areas of low sand supply. On Georges Bank, the management of resources and habitats requires an understanding of the distribution of substrate types, their surface dynamics and susceptibility to movement, and their associated fauna.

A Numerical Modeling Framework for Cohesive Sediment Transport Driven by Waves and Tidal Currents

DTIC Science & Technology

2012-09-30

for sediment transport. The successful extension to multi-dimensions is benefited from an open-source CFD package, OpenFOAM (www.openfoam.org). This...linz.at/Drupal/), which couples the fluid solver OpenFOAM with the Discrete Element Model (DEM) solver LIGGGHTS (an improved LAMMPS for granular flow

A numerical study of three-dimensional diurnal variations within the thermosphere.

NASA Technical Reports Server (NTRS)

Volland, H.; Mayr, H. G.

1973-01-01

A thermosphere model with a realistic temperature profile is assumed. Heat conduction waves are introduced in addition to gravity waves. The temporal and spatial distribution of ion-neutral collisions is taken into account. However, the influence of viscosity waves is neglected. Viscosity-wave effects are simulated by an effective height-dependent collision number. Numerical calculations are conducted of the generation and propagation of two of the most important symmetric tidal waves at thermospheric heights. The influence of the solar EUV-heat upon the generation of the two tidal modes is investigated.

Scylla and Charybdis observed from space

NASA Astrophysics Data System (ADS)

Alpers, Werner; Salusti, Ettore

1983-02-01

Scylla and Charybdis are, in Greek mythology, two immortal and irresistible monsters who beset the narrow waters separating the Italian peninsula from Sicily. They give poetic expressions to exceptional oceanographic features encountered in the Strait of Messina. Recently, the SEASAT satellite has added new information on the oceanography of this strait. For the first time, experimental evidence is presented that internal waves are generated in the Strait of Messina. The generation mechanism is linked to tidal currents washing over the shallow sill within the strait. The experimental data originate from a synthetic aperture radar (SAR) image obtained from the SEASAT satellite on Sept, 15, 1978, and from subsequent in situ measurements carried out from the Italian research vessel Bannock in Nov. 1980. The circular wave pattern visible on the SEASAT SAR image is interpreted in terms of internal solitons. Furthermore, the SEASAT SAR image also reveals `tagli,' special types of tidal bores, encountered in the Strait of Messina.

High-resolution velocimetry in energetic tidal currents using a convergent-beam acoustic Doppler profiler

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sellar, Brian; Harding, Samuel F.; Richmond, Marshall C.

An array of convergent acoustic Doppler velocimeters has been developed and tested for the high resolution measurement of three-dimensional tidal flow velocities in an energetic tidal site. This configuration has been developed to increase spatial resolution of velocity measurements in comparison to conventional acoustic Doppler profilers (ADPs) which characteristically use diverging acoustic beams emanating from a single instrument. This is achieved using converging acoustic beams with a sample volume at the focal point of 0.03 m 3. The array is also able to simultaneously measure three-dimensional velocity components in a profile throughout the water column, and as such is referredmore » to herein as a converging-beam acoustic Doppler profiler (CADP). Mid-depth profiling is achieved through integration of the sensor platform with the operational Alstom 1MW DeepGen-IV Tidal Turbine. This proof-of-concept paper outlines system configuration and comparison to measurements provided by co-installed reference instrumentation. Comparison of CADP to standard ADP velocity measurements reveals a mean difference of 8 mm/s, standard deviation of 18 mm/s, and order-of-magnitude reduction in realizable length-scale. CADP focal point measurements compared to a proximal single-beam reference show peak cross-correlation coefficient of 0.96 over 4.0 s averaging period and a 47% reduction in Doppler noise. The dual functionality of the CADP as a profiling instrument with a high resolution focal point make this configuration a unique and valuable advancement in underwater velocimetry enabling improved turbulence, resource and structural loading quantification and validation of numerical simulations. Alternative modes of operation have been implemented including noise-reducing bi-static sampling. Since waves are simultaneously measured it is expected that derivatives of this system will be a powerful tool in wave-current interaction studies.« less

The effect of lagoons on Adriatic Sea tidal dynamics

NASA Astrophysics Data System (ADS)

Ferrarin, Christian; Maicu, Francesco; Umgiesser, Georg

2017-11-01

In this study the effects that lagoons exert on the barotropic tidal dynamics of a regional sea, the Adriatic Sea, were numerically explored. This semi-enclosed basin is one of the places with the highest tidal range in the Mediterranean Sea and is characterised by the presence of several lagoons in its northern part. The tidal dynamics of a system comprising the whole Adriatic Sea and the lagoons of Venice, Marano-Grado and Po Delta were investigated using an unstructured hydrodynamic model. Numerical experiments with and without lagoons reveal that even if the considered shallow water bodies represent only the 0.5 and 0.002% of the Adriatic Sea surface and volume, respectively, they significantly affect the entire Northern Adriatic Sea tidal dynamics by enhancing tidal range (by 5%) and currents (by 10%). The inclusion of lagoons in the computation improved the model performance by 25% in reproducing tidal constituents in the Adriatic Sea. The back-effect of the lagoons on the open-sea tide is due to the waves radiating from the co-oscillating lagoons into the adjacent sea. This is the first time these processes are shown to be relevant for the Adriatic Sea, thus enhancing the understanding of the tidal dynamics in this regional sea. These findings may also apply to other coastal seas with connections to lagoons, bays and estuaries.

Wave-driven fluxes through New River Inlet, NC

NASA Astrophysics Data System (ADS)

Wargula, A.; Raubenheimer, B.; Elgar, S.

2012-12-01

The importance of wave forcing to inlet circulation is examined using observations of waves, water levels, and currents collected in and near New River Inlet, NC during April and May, 2012. A boat-mounted system was used to measure current profiles along transects across the inlet mouth during three 14-hr periods, providing information on cross-inlet current structure, as well as discharge. Additionally, an array of 13 colocated pressure gages and profilers were deployed along 2 km of the inlet channel (5 to 10 m water depths) and ebb shoal channel (2 to 3 m water depths) and 19 colocated pressure gages and acoustic Doppler velocimeters were deployed across and offshore of the ebb shoal (1 to 5 m water depths) (Figure 1). The inlet is well mixed and tidal currents ranged from +/- 1.5 m/s, maximum discharge rates at peak ebb and flood were about 700 to 900 m3/s, offshore significant wave heights Hsig were 0.5 to 2.5 m, and wind speeds ranged from 0 to 14 m/s. Time-integrated residual discharge over semi-diurnal tidal cycles with similar ranges was ebb dominant during calm conditions (May 11, net out-of-inlet discharge ~ 55 m3, Hsig ~ 0.5 m, NW winds ~ 3 m/s) and flood dominant during stormier conditions (May 14, net into-inlet discharge ~ 15 m3, Hsig ~ 1.2 m, S winds ~ 6.5 m/s). Low-pass filtered in situ profiler data suggest wave-forcing affects the fluxes into and out of the inlet. The observations will be used to examine the momentum balance governing the temporal and cross-inlet (channel vs. shoal) variation of these fluxes, as well as the effect of waves on ebb and flood flow dominance. Funding provided by the Office of Naval Research and a National Security Science and Engineering Faculty Fellowship.; Figure 1: Google Earth image of New River Inlet, NC. Colors are depth contours (scale on the right, units are m relative to mean sea level) and symbols are locations of colocated current meters and pressure gages.

Measurement of Underwater Operational Noise Emitted by Wave and Tidal Stream Energy Devices.

PubMed

Lepper, Paul A; Robinson, Stephen P

2016-01-01

The increasing international growth in the development of marine and freshwater wave and tidal energy harvesting systems has been followed by a growing requirement to understand any associated underwater impact. Radiated noise generated during operation is dependent on the device's physical properties, the sound-propagation environment, and the device's operational state. Physical properties may include size, distribution in the water column, and mechanics/hydrodynamics. The sound-propagation environment may be influenced by water depth, bathymetry, sediment type, and water column acoustic properties, and operational state may be influenced by tidal cycle and wave height among others This paper discusses some of the challenges for measurement of noise characteristics from these devices as well as a case study of the measurement of radiated noise from a full-scale wave energy converter.

An operational coupled wave-current forecasting system for the northern Adriatic Sea

NASA Astrophysics Data System (ADS)

Russo, A.; Coluccelli, A.; Deserti, M.; Valentini, A.; Benetazzo, A.; Carniel, S.

2012-04-01

Since 2005 an Adriatic implementation of the Regional Ocean Modeling System (AdriaROMS) is being producing operational short-term forecasts (72 hours) of some hydrodynamic properties (currents, sea level, temperature, salinity) of the Adriatic Sea at 2 km horizontal resolution and 20 vertical s-levels, on a daily basis. The main objective of AdriaROMS, which is managed by the Hydro-Meteo-Clima Service (SIMC) of ARPA Emilia Romagna, is to provide useful products for civil protection purposes (sea level forecasts, outputs to run other forecasting models as for saline wedge, oil spills and coastal erosion). In order to improve the forecasts in the coastal area, where most of the attention is focused, a higher resolution model (0.5 km, again with 20 vertical s-levels) has been implemented for the northern Adriatic domain. The new implementation is based on the Coupled-Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST)and adopts ROMS for the hydrodynamic and Simulating WAve Nearshore (SWAN) for the wave module, respectively. Air-sea fluxes are computed using forecasts produced by the COSMO-I7 operational atmospheric model. At the open boundary of the high resolution model, temperature, salinity and velocity fields are provided by AdriaROMS while the wave characteristics are provided by an operational SWAN implementation (also managed by SIMC). Main tidal components are imposed as well, derived from a tidal model. Work in progress is oriented now on the validation of model results by means of extensive comparisons with acquired hydrographic measurements (such as CTDs or XBTs from sea-truth campaigns), currents and waves acquired at observational sites (including those of SIMC, CNR-ISMAR network and its oceanographic tower, located off the Venice littoral) and satellite-derived wave-heights data. Preliminary results on the forecast waves denote how, especially during intense storms, the effect of coupling can lead to significant variations in the wave heights. Part of the activity has been funded by the EU FP VII program (project "MICORE", contract n. 202798) and by the Regione Veneto regional law 15/2007 (Progetto "MARINA").

Lunar tidal effects during the 2013 stratospheric sudden warming as simulated by the TIME-GCM

NASA Astrophysics Data System (ADS)

Maute, A. I.; Forbes, J. M.; Zhang, X.; Fejer, B. G.; Yudin, V. A.; Pedatella, N. M.

2015-12-01

Stratospheric Sudden Warmings (SSW) are associated with strong planetary wave activity in the winterpolar stratosphere which result in a very disturbed middle atmosphere. The changes in the middle atmospherealter the propagation conditions and the nonlinear interactions of waves and tides, and result in SSW signals in the upper atmosphere in e.g., neutral winds, electric fields, ionospheric currents and plasma distribution. The upper atmosphere changes can be significant at low-latitudes even during medium solar flux conditions. Observationsalso reveal a strong lunar signal during SSW periods in the low latitude vertical drifts and in ionospheric quantities. Forbes and Zhang [2012] demonstrated that during the 2009 SSW period the Pekeris resonance peak of the atmosphere was altered such that the M2 and N2 lunar tidal componentsgot amplified. This study focuses on the effect of the lunar tidal forcing on the thermosphere-ionosphere system during theJanuary 2013 SSW period. We employthe NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM)with a nudging scheme using the Whole-Atmosphere-Community-Climate-Model-Extended (WACCM-X)/Goddard Earth Observing System Model, Version 5 (GEOS5) results to simulate the effects of meteorological forcing on the upper atmosphere. Additionally lunar tidal forcingis included at the lower boundary of the model. To delineate the lunar tidal effects a base simulation without lunar forcingis employed. Interestingly, Jicamarca observations of that period reveal a suppression of the daytime vertical drift before and after the drift enhancement due the SSW. The simulation suggests that the modulation of the vertical driftmay be caused by the interplay of the migrating solar and lunar semidiurnal tide, and therefore can only be reproduced by the inclusion of both lunar and solar tidal forcings in the model. In this presentation the changes due to the lunar tidal forcing will be quantified, and compared to observations.

Tidal currents and anticyclonic motions on two North Pacific seamounts

USGS Publications Warehouse

Genin, A.; Noble, M.; Lonsdale, P.F.

1989-01-01

Near-bottom currents were measured for several days at three sites on the summits of Fieberling Guyot (32??26???N, 127??46???W) and Horizon Guyot (19??15???N, 160??00???W). Three moorings comprised of two current meters were deployed on each summit; two moorings were deployed on opposite sides of the rim of the summit and one mooring was deployed near the center of the summit. The observed currents were strong, with maximum speeds of 48 and 24 cm s-1 on Fieberling and Horizon, respectively. The currents at specific frequencies were enhanced relative to those in the surrounding ocean. Diurnal currents were the dominant component of the current field on Fieberling Guyot. They accounted for 39-68% of the energy and had amplitudes around 12 cm s-1. We suspect that these diurnal currents were waves trapped over the seamount. Semidiurnal internal tidal currents were the strongest currents over Horizon Guyot, with amplitudes around 4 cm s-1. The flow patterns determined in this study seemed to affect the biological and geological characteristics of the seamounts. ?? 1990.

Tidal river dynamics: Implications for deltas

NASA Astrophysics Data System (ADS)

Hoitink, A. J. F.; Jay, D. A.

2016-03-01

Tidal rivers are a vital and little studied nexus between physical oceanography and hydrology. It is only in the last few decades that substantial research efforts have been focused on the interactions of river discharge with tidal waves and storm surges into regions beyond the limit of salinity intrusion, a realm that can extend inland hundreds of kilometers. One key phenomenon resulting from this interaction is the emergence of large fortnightly tides, which are forced long waves with amplitudes that may increase beyond the point where astronomical tides have become extinct. These can be larger than the linear tide itself at more landward locations, and they greatly influence tidal river water levels and wetland inundation. Exploration of the spectral redistribution and attenuation of tidal energy in rivers has led to new appreciation of a wide range of consequences for fluvial and coastal sedimentology, delta evolution, wetland conservation, and salinity intrusion under the influence of sea level rise and delta subsidence. Modern research aims at unifying traditional harmonic tidal analysis, nonparametric regression techniques, and the existing understanding of tidal hydrodynamics to better predict and model tidal river dynamics both in single-thread channels and in branching channel networks. In this context, this review summarizes results from field observations and modeling studies set in tidal river environments as diverse as the Amazon in Brazil, the Columbia, Fraser and Saint Lawrence in North America, the Yangtze and Pearl in China, and the Berau and Mahakam in Indonesia. A description of state-of-the-art methods for a comprehensive analysis of water levels, wave propagation, discharges, and inundation extent in tidal rivers is provided. Implications for lowland river deltas are also discussed in terms of sedimentary deposits, channel bifurcation, avulsion, and salinity intrusion, addressing contemporary research challenges.

Evaluating wave-current interaction in an urban estuary and flooding implications for coastal communities

NASA Astrophysics Data System (ADS)

Cifuentes-Lorenzen, A.; O'Donnell, J.; Howard-Strobel, M. M.; Fake, T.; McCardell, G.

2016-12-01

Accurate hydrodynamic-wave coupled coastal circulation models aid the prediction of storm impacts, particularly in areas where data is absent, and can inform mitigation options. They are essential everywhere to account for the effects of climate change. Here, the Finite Volume Community Ocean Model (FVCOM) was used to estimate the residual circulation inside a small urban estuary, Long Island Sound, during three severe weather events of different magnitude (i.e. 1/5, 1/25 and 1/50 year events). The effect of including wave coupling using a log-layer bottom boundary and the bottom wave-current coupling, following the approach of Madsen (1994) on the simulated residual circulation was assessed. Significant differences in the solutions were constrained to the near surface (s>-0.3) region. No significant difference in the depth-averaged residual circulation was detected. When the Madsen (1994) bottom boundary layer model for wave-current interaction was employed, differences in residual circulation resulted. The bottom wave-current interaction also plays an important role in the wave dynamics. Significant wave heights along the northern Connecticut shoreline were enhanced by up to 15% when the bottom wave-current interaction was included in the simulations. The wave-induced bottom drag enhancement has a substantial effect on tides in the Sound, possibly because it is nearly resonant at semidiurnal frequencies. This wave-current interaction current leads to severe tidal dampening ( 40% amplitude reduction) at the Western end of the estuary in the modeled sea surface displacement. The potential magnitude of these effects means that wave current interaction should be included and carefully evaluated in models of estuaries that are useful.

Storm-induced water dynamics and thermohaline structure at the tidewater Flade Isblink Glacier outlet to the Wandel Sea (NE Greenland)

NASA Astrophysics Data System (ADS)

Kirillov, Sergei; Dmitrenko, Igor; Rysgaard, Søren; Babb, David; Toudal Pedersen, Leif; Ehn, Jens; Bendtsen, Jørgen; Barber, David

2017-11-01

In April 2015, an ice-tethered conductivity-temperature-depth (CTD) profiler and a down-looking acoustic Doppler current profiler (ADCP) were deployed from the landfast ice near the tidewater glacier terminus of the Flade Isblink Glacier in the Wandel Sea, NE Greenland. The 3-week time series showed that water dynamics and the thermohaline structure were modified considerably during a storm event on 22-24 April, when northerly winds exceeded 15 m s-1. The storm initiated downwelling-like water dynamics characterized by on-shore water transport in the surface (0-40 m) layer and compensating offshore flow at intermediate depths. After the storm, currents reversed in both layers, and the relaxation phase of downwelling lasted ˜ 4 days. Although current velocities did not exceed 5 cm s-1, the enhanced circulation during the storm caused cold turbid intrusions at 75-95 m depth, which are likely attributable to subglacial water from the Flade Isblink Ice Cap. It was also found that the semidiurnal periodicities in the temperature and salinity time series were associated with the lunar semidiurnal tidal flow. The vertical structure of tidal currents corresponded to the first baroclinic mode of the internal tide with a velocity minimum at ˜ 40 m. The tidal ellipses rotate in opposite directions above and below this depth and cause a divergence of tidal flow, which was observed to induce semidiurnal internal waves of about 3 m height at the front of the glacier terminus. Our findings provide evidence that shelf-basin interaction and tidal forcing can potentially modify coastal Wandel Sea waters even though they are isolated from the atmosphere by landfast sea ice almost year-round. The northerly storms over the continental slope cause an enhanced circulation facilitating a release of cold and turbid subglacial water to the shelf. The tidal flow may contribute to the removal of such water from the glacial terminus.

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait.

PubMed

Droghei, R; Falcini, F; Casalbore, D; Martorelli, E; Mosetti, R; Sannino, G; Santoleri, R; Chiocci, F L

2016-11-03

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary "current" that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Detection of Gravitational Wave Emission by Supermassive Black Hole Binaries Through Tidal Disruption Flares.

PubMed

Hayasaki, Kimitake; Loeb, Abraham

2016-10-21

Galaxy mergers produce supermassive black hole binaries, which emit gravitational waves prior to their coalescence. We perform three-dimensional hydrodynamic simulations to study the tidal disruption of stars by such a binary in the final centuries of its life. We find that the gas stream of the stellar debris moves chaotically in the binary potential and forms accretion disks around both black holes. The accretion light curve is modulated over the binary orbital period owing to relativistic beaming. This periodic signal allows to detect the decay of the binary orbit due to gravitational wave emission by observing two tidal disruption events that are separated by more than a decade.

Evidence of gravity wave-tidal interaction observed near the summer mesopause at Poker Flat, Alaska

NASA Technical Reports Server (NTRS)

Wang, Ding-Yi; Fritts, David C.

1991-01-01

An analysis of gravity wave-tidal interaction observed near the mesopause by the MST radar at Poker Flat in July of 1986 is presented. The observations revealed daily mean wind maxima of about 60 m/sec westward and 20 m/sec southward with daily mean momentum fluxes, contributed by gravity waves with periods less than 1 hour of 4-5 sq m/sec sq eastward and 1-2 sq m/sec sq northward. Considerable hourly height variability was found to exist for both winds and momentum fluxes. A significant modulation of the fluxes by tidal winds was observed, characterized by out-of-phase correlations over a number of heights.

Detection of Gravitational Wave Emission by Supermassive Black Hole Binaries Through Tidal Disruption Flares

PubMed Central

Hayasaki, Kimitake; Loeb, Abraham

2016-01-01

Galaxy mergers produce supermassive black hole binaries, which emit gravitational waves prior to their coalescence. We perform three-dimensional hydrodynamic simulations to study the tidal disruption of stars by such a binary in the final centuries of its life. We find that the gas stream of the stellar debris moves chaotically in the binary potential and forms accretion disks around both black holes. The accretion light curve is modulated over the binary orbital period owing to relativistic beaming. This periodic signal allows to detect the decay of the binary orbit due to gravitational wave emission by observing two tidal disruption events that are separated by more than a decade. PMID:27767188

A 20-Year High-Resolution Wave Resource Assessment of Japan with Wave-Current Interactions

NASA Astrophysics Data System (ADS)

Webb, A.; Waseda, T.; Kiyomatsu, K.

2016-02-01

Energy harvested from surface ocean waves and tidal currents has the potential to be a significant source of green energy, particularly for countries with extensive coastlines such as Japan. As part of a larger marine renewable energy project*, The University of Tokyo (in cooperation with JAMSTEC) has conducted a state-of-the-art wave resource assessment (with uncertainty estimates) to assist with wave generator site identification and construction in Japan. This assessment will be publicly available and is based on a large-scale NOAA WAVEWATCH III (version 4.18) simulation using NCEP and JAMSTEC forcings. It includes several key components to improve model skill: a 20-year simulation to reduce aleatory uncertainty, a four-nested-layer approach to resolve a 1 km shoreline, and finite-depth and current effects included in all wave power density calculations. This latter component is particularly important for regions near strong currents such as the Kuroshio. Here, we will analyze the different wave power density equations, discuss the model setup, and present results from the 20-year assessment (with a focus on the role of wave-current interactions). Time permitting, a comparison will also be made with simulations using JMA MSM 5 km winds. *New Energy and Industrial Technology Development Organization (NEDO): "Research on the Framework and Infrastructure of Marine Renewable Energy; an Energy Potential Assessment"

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, R.J.; Johnson, C.A.; Gilreath, J.A.

Depositional systems in the Medina Group (Lower Silurian) of western New York have been studied using stratigraphic dipmeter data. Results of this study indicate a nearshore-deltaic-interdeltaic depositional environment. Only minor deltaic episodes are preserved in the study area. This fits the generally arid climate with seasonal wet periods suggested by C.D. Laughrey. Facies recognized include: longshore-current sand waves in a shoreface environment, distributary mouth bars, distributary channels, tidal inlets, flood deltas, beaches, sandy tidal flats on which beach ridges were formed, and possible upper delta-plain sediments. Once the depositional sequences are recognized, paleocurrents within key sand units can be interpretedmore » to determine favorable directions for successfully locating offset wells.« less

Internal gravity wave contributions to global sea surface variability

NASA Astrophysics Data System (ADS)

Savage, A.; Arbic, B. K.; Richman, J. G.; Shriver, J. F.; Buijsman, M. C.; Zamudio, L.; Wallcraft, A. J.; Sharma, H.

2016-02-01

High-resolution (1/12th and 1/25th degree) 41-layer simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea-surface height (SSH). The HYCOM output has been separated into steric, non-steric, and total sea-surface height and the maps display variance in subtidal, tidal, and supertidal bands. Two of the global maps are of particular interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) wide-swath satellite altimeter mission; (1) a map of the nonstationary tidal signal (estimated after removing the stationary tidal signal via harmonic analysis), and (2) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum. Both of these maps display signals of order 1 cm2, the target accuracy for the SWOT mission. Therefore, both non-stationary internal tides and non-tidal internal gravity waves are likely to be important sources of "noise" that must be accurately removed before examination of lower-frequency phenomena can take place.

Seasonal sedimentary processes of the macrotidal flat in Gomso Bay, west coast of Korea

NASA Astrophysics Data System (ADS)

Woo, H.; Kang, J.; Choi, J.

2012-12-01

The tidal flats on the west coast of Korea have broad zones with gentle slopes and a macrotidal setting with 4 to 10 meters of tidal ranges. They are directly influenced by monsoons and heavily affected by waves in winter and tidal currents in summer. As a result, most western tidal flats show the seasonal changes of sedimentary features comprising sedimentation and/or erosion of sediments. Gomso bay in the mid-west of Korea is a funnel-shaped embayment with a wide entrance to the west. Tides are semidiurnal and macrotidal, with a mean tidal range of 433.8 cm. Digital elevation model (DEM) showed that the landward inner bay had mainly high elevations and the seaward outer bay had relatively low elevations. In particular, there are considerable gradients in the outer bay from area of high-water line to area of low-water line. The sedimentary analysis and monitoring short-term sedimentation rates were investigated to understand seasonal sedimentary processes of tidal flats in Gomso bay. The surface sediments in the bay were classified into five sedimentary facies in spring 2011. Generally, sandy sediments were dominated in the outer bay, whereas sandy mud sediments were distributed on the inner bay. The middle bay mainly consisted of muddy sand sediments. The percentages of sand decreased from outer to inner bay. The short-term sedimentation rates were obtained from three lines by burying a plate at sub-bottom depth and periodically measuring the changing sediment depth from February 2011 to February 2012. In the tidal flat at inner bay (KB- Line), the annual sedimentation rates were ranged -8.87 to 74.69 mm/year with the net deposition rate of 40.90 mm/year. The deposition occurred on KB-Line in spring, autumn and winter. The erosion was dominated on the tidal flats at middle (KH-Line) and outer bay (KM-Line) during autumn and winter with an annual erosion rate of -29.86 mm/year and -9.92 mm/year, respectively. The seasonal variations of sedimentation on these tidal flats showed that the deposition occurred with an inflow of muddy sediments in summer, whereas the erosion was dominated in autumn and winter. In August 2011, the distribution patterns of rare earth elements (REEs) relative to the upper continental crust (UCC) showed the enrichment of light REEs (LREEs: La-Nd), together with an apparent depletion of Eu in the KH- and KM-Lines. This pattern was more pronounced in the middle bay sediments (KH-Line) due to influence of muddy sediment transport from Jujin Stream during the rainy period (July and August). On the other hand, the outer bay sediments in the KM-Line were reflected more inflow of second sediment source, the Geum River. The major control factors for seasonal variations of sediments on the tidal flat could be heavy rainfall and tidal currents during summer and strong waves during winter. The net sedimentation showed that the deposition occurred in the inner tidal flat and erosion occurred in the middle and outer tidal flat of the bay.

Transient tidal eddy motion in the western Gulf of Maine, part 1: Primary structure

NASA Astrophysics Data System (ADS)

Brown, W. S.; Marques, G. M.

2013-07-01

High frequency radar-derived surface current maps of the Great South Channel (GSC) in the western Gulf of Maine in 2005 revealed clockwise (CW) and anticlockwise (ACW) eddy motion associated with the strong regional tidal currents. To better elucidate the kinematics and dynamics of these transient tidal eddy motions, an observational and modeling study was conducted during the weakly stratified conditions of winter 2008-2009. Our moored bottom pressure and ADCP current measurements in 13m depth were augmented by historical current measurements in about 30m in documenting the dominance of highly polarized M2 semidiurnal currents in our nearshore study region. The high-resolution finite element coastal ocean model (QUODDY) - forced by the five principal tidal constituents - produced maps depicting the formation and evolution of the CW and ACW eddy motions that regularly follow maximum ebb and flood flows, respectively. Observation versus model current comparison required that the model bottom current drag coefficient be set to at an unusually high Cd=0.01 - suggesting the importance of form drag in the study region. The observations and model results were consistent in diagnosing CW or ACW eddy motions that (a) form nearshore in the coastal boundary layer (CBL) for about 3h after the respective tidal current maxima and then (b) translate southeastward across the GSC along curved 50m isobath at speeds of about 25m/s. Observation-based and model-based momentum budget estimates were consistent in showing a first order forced semidiurnal standing tidal wave dynamics (like the adjacent Gulf of Maine) which was modulated by adverse pressure gradient/bottom stress forcing to generate the eddy motions. Observation-based estimates of terms in the transport vorticity budget showed that in the shallower Inner Zone subregion (average depth=23m) that the diffusion of nearshore vorticity was dominant in feeding the growth of eddy motion vorticity; while in the somewhat deeper Outer Zone subregion (33m) bottom current lateral shear and water column stretching/squashing was significant in modulating the eddy motion. We conclude that the transient eddy motions in the GSC region are phase eddies that accompany the change of tide across the GSC and are (1) generated by bottom stress gradients in the shallower nearshore - an issue which needs to be better understood for improved future forecasting.

Wave and Current Observations in a Tidal Inlet Using GPS Drifter Buoys

DTIC Science & Technology

2013-03-01

right panel). ............17  Figure 10.  DWR-G external sensor configuration (left panel). GT-31 GPS receiver is visible on the bottom left. Two GoPro ...receiver is visible on the bottom left. Two GoPro cameras are attached to the top of the buoy. DWR-G internal sensor configuration (right panel

Long-term, high-frequency current and temperature measurements along central California: Insights into upwelling/relaxation and internal waves on the inner shelf

USGS Publications Warehouse

Storlazzi, C.D.; McManus, M.A.; Figurski, J.D.

2003-01-01

Thermistor chains and acoustic Doppler current profilers were deployed at the northern and southern ends of Monterey Bay to examine the thermal and hydrodynamic structure of the inner (h ??? 20 m) shelf of central California. These instruments sampled temperature and current velocity at 2-min intervals over a 13-month period from June 2000 to July 2001. Time series of these data, in conjunction with SST imagery and CODAR sea surface current maps, helped to establish the basic hydrography for Monterey Bay. Analysis of time series data revealed that depth integrated flow at both sites was shore parallel (northwest-southeast) with net flows out of the Bay (northwest). The current and temperature records were dominated by semi-diurnal and diurnal tidal signals that lagged the surface tides by 3 h on average. Over the course of an internal tidal cycle these flows were asymmetric, with the flow during the flooding internal tide to the southeast typically lasting only one-third as long as the flow to the northwest during the ebbing internal tide. The transitions from ebb to flood were rapid and bore-like in nature; they were also marked by rapid increases in temperature and high shear. During the spring and summer, when thermal stratification was high, we observed almost 2000 high-frequency (Tp ??? 4-20 min) internal waves in packets of 8-10 following the heads of these bore-like features. Previous studies along the West Coast of the US have concluded that warm water bores and high-frequency internal waves may play a significant role in the onshore transport of larvae.

The Influence of Surface Gravity Waves on Marine Current Turbine Performance

NASA Astrophysics Data System (ADS)

Lust, E.; Luznik, L.; Flack, K. A.; Walker, J.; Van Benthem, M.

2013-12-01

Surface gravity waves can significantly impact operating conditions for a marine current turbine, imparting unsteady velocities several orders of magnitude larger than the ambient turbulence. The influence of surface waves on the performance characteristics of a two-bladed horizontal axis marine current turbine was investigated experimentally in a large towing tank facility at the United States Naval Academy. The turbine model had a 0.8 m diameter (D) rotor with a NACA 63-618 cross section, which is Reynolds number independent with respect to lift coefficient in the operating range of Rec ≈ 4 x 105. The torque, thrust and rotational speed were measured at a range of tip speed ratios (TSR) from 5 < TSR < 11. Tests were performed at two rotor depths (1.3D and 2.25D) with and without waves. The average turbine performance characteristics were largely unchanged by depth or the presence of waves. However, tests with waves indicate large variations in thrust, rotational speed, and torque occurred with the passage of the wave. These results demonstrate the impact of surface gravity waves on power production and structural loading and suggest that turbines should be positioned vertically within the water column at a depth which maximizes power output while minimizing material fatigue. Keywords-- marine current turbine, tidal turbine, towing-tank experiments, surface gravity waves, fatigue loading, phase averaging

High-Accuracy Tidal Flat Digital Elevation Model Construction Using TanDEM-X Science Phase Data

NASA Technical Reports Server (NTRS)

Lee, Seung-Kuk; Ryu, Joo-Hyung

2017-01-01

This study explored the feasibility of using TanDEM-X (TDX) interferometric observations of tidal flats for digital elevation model (DEM) construction. Our goal was to generate high-precision DEMs in tidal flat areas, because accurate intertidal zone data are essential for monitoring coastal environment sand erosion processes. To monitor dynamic coastal changes caused by waves, currents, and tides, very accurate DEMs with high spatial resolution are required. The bi- and monostatic modes of the TDX interferometer employed during the TDX science phase provided a great opportunity for highly accurate intertidal DEM construction using radar interferometry with no time lag (bistatic mode) or an approximately 10-s temporal baseline (monostatic mode) between the master and slave synthetic aperture radar image acquisitions. In this study, DEM construction in tidal flat areas was first optimized based on the TDX system parameters used in various TDX modes. We successfully generated intertidal zone DEMs with 57-m spatial resolutions and interferometric height accuracies better than 0.15 m for three representative tidal flats on the west coast of the Korean Peninsula. Finally, we validated these TDX DEMs against real-time kinematic-GPS measurements acquired in two tidal flat areas; the correlation coefficient was 0.97 with a root mean square error of 0.20 m.

Linking channel hydrology with riparian wetland accretion in tidal rivers

USGS Publications Warehouse

Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.

2014-01-01

The hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood, yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the non-tidal through oligohaline portion of two coastal plain rivers in Maryland, U.S.A., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a one year period using artificial marker horizons, channel hydrology was measured over a one month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the non-tidal sites (mean and standard deviation = 8 ± 8 mm yr-1), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr-1), low at the midstream TFFW (12 ± 9 mm yr-1), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr-1). Channel maximum flood and ebb velocity was 2-fold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: the oligohaline zone's SSC was more than double the tidal freshwater zone's, and was greater than historical SSC at the non-tidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. Overall sediment accretion was higher in the embayed river likely due to a single storm discharge and associated sedimentation.

Waves and tides responsible for the intermittent closure of the entrance of a small, sheltered tidal wetland at San Francisco, CA

USGS Publications Warehouse

Hanes, D.M.; Ward, K.; Erikson, L.H.

2011-01-01

Crissy Field Marsh (CFM; http://www.nps.gov/prsf/planyourvisit/crissy-field-marsh-and-beach.htm) is a small, restored tidal wetland located in the entrance to San Francisco Bay just east of the Golden Gate. The marsh is small but otherwise fairly typical of many such restored wetlands worldwide. The marsh is hydraulically connected to the bay and the adjacent Pacific Ocean by a narrow sandy channel. The channel often migrates and sometimes closes completely, which effectively blocks the tidal connection to the ocean and disrupts the hydraulics and ecology of the marsh. Field measurements of waves and tides have been examined in order to evaluate the conditions responsible for the intermittent closure of the marsh entrance. The most important factor found to bring about the entrance channel closure is the occurrence of large ocean waves. However, there were also a few closure events during times with relatively small offshore waves. Examination of the deep-water directional wave spectra during these times indicates the presence of a small secondary peak corresponding to long period swell from the southern hemisphere, indicating that CFM and San Francisco Bay in general may be more susceptible to long period ocean swell emanating from the south or southwest than the more common ocean waves coming from the northwest. The tidal records during closure events show no strong relationship between closures and tides, other than that closures tend to occur during multi-day periods with successively increasing high tides. It can be inferred from these findings that the most important process to the intermittent closure of the entrance to CFM is littoral sediment transport driven by the influence of ocean swell waves breaking along the CFM shoreline at oblique angles. During periods of large, oblique waves the littoral transport of sand likely overwhelms the scour potential of the tidal flow in the entrance channel. ?? 2011.

Tidal Love numbers of neutron and self-bound quark stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Postnikov, Sergey; Prakash, Madappa; Lattimer, James M.

Gravitational waves from the final stages of inspiraling binary neutron stars are expected to be one of the most important sources for ground-based gravitational wave detectors. The masses of the components are determinable from the orbital and chirp frequencies during the early part of the evolution, and large finite-size (tidal) effects are measurable toward the end of inspiral, but the gravitational wave signal is expected to be very complex at this time. Tidal effects during the early part of the evolution will form a very small correction, but during this phase the signal is relatively clean. The accumulated phase shiftmore » due to tidal corrections is characterized by a single quantity related to a star's tidal Love number. The Love number is sensitive, in particular, to the compactness parameter M/R and the star's internal structure, and its determination could provide an important constraint to the neutron star radius. We show that Love numbers of self-bound strange quark matter stars are qualitatively different from those of normal neutron stars. Observations of the tidal signature from coalescing compact binaries could therefore provide an important, and possibly unique, way to distinguish self-bound strange quark stars from normal neutron stars. Tidal signatures from self-bound strange quark stars with masses smaller than 1M{sub {center_dot}}are substantially smaller than those of normal stars owing to their smaller radii. Thus tidal signatures of stars less massive than 1M{sub {center_dot}}are probably not detectable with Advanced LIGO. For stars with masses in the range 1-2M{sub {center_dot},} the anticipated efficiency of the proposed Einstein telescope would be required for the detection of tidal signatures.« less

Observation of sand waves in the Taiwan Banks using HJ-1A/1B sun glitter imagery

NASA Astrophysics Data System (ADS)

Zhang, Hua-guo; Lou, Xiu-lin; Shi, Ai-qin; He, Xie-kai; Guan, Wei-bing; Li, Dong-ling

2014-01-01

This study focuses on the large sand waves in the Taiwan Banks. Our goals are to observe the sand waves as completely as possible, to obtain their direction, wavelength, density, and ridge length, to analyze their spatial distributions, and to understand the effects of the current field and water depth on the sand waves. This study demonstrates the possibility of using HJ-1A/1B sun glitter imagery with a large swath width and rapid coverage in studying sand waves. Six cloud-free HJ-1A/1B optical images with sun glitter signals received during 2009 to 2011 were processed. The sand waves were mapped based on their features in the images; their direction, wavelength, density, and ridge length were measured and analyzed. We identified 4604 sand waves distributed in an area of 16,400 km2. The distributions of sand waves and their characteristics were analyzed, and the differences of sand waves between the northwestern subregion and the southeastern subregion are reported. Further analysis and discussion of the relationships between spatial distribution of the sand waves and both the tidal current field from a numerical simulation and water depth led to some interesting conclusions. The current field determines the orientation of the sand wave, while the hydrodynamic conditions and water depth influence the shape, size, and density of sand waves to a certain degree.

Modulation of Gravity Waves by Tides as Seen in CRISTA Temperatures

NASA Technical Reports Server (NTRS)

Preusse, P.; Eckermann, S. D.; Oberheide, J.; Hagan, M. E.; Offermann, D.

2001-01-01

During shuttle missions STS-66 (November, 1994) and STS-85 (August, 1997) the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) acquired temperature data with very high spatial resolution. These are analyzed for gravity waves (GW). The altitude range spans the whole middle atmosphere from the tropopause up to the mesopause. In the upper mesosphere tidal amplitudes exceed values of 10 K. Modulation of GW activity by the tides is observed and analyzed using CRISTA temperatures and tidal predictions of the Global Scale Wave Model (GSWM). The modulation process is identified as a tidally-induced change of the background buoyancy frequency. The findings agree well with the expectations for saturated GW and are the first global scale observations of this process.

On the generation and evolution of internal solitary waves in the southern Red Sea

NASA Astrophysics Data System (ADS)

Guo, Daquan; Zhan, Peng; Kartadikaria, Aditya; Akylas, Triantaphyllos; Hoteit, Ibrahim

2015-04-01

Satellite observations recently revealed the existence of trains of internal solitary waves in the southern Red Sea between 16.0°N and 16.5°N, propagating from the centre of the domain toward the continental shelf [Da silva et al., 2012]. Given the relatively weak tidal velocity in this area and their generation in the central of the domain, Da Silva suggested three possible mechanisms behind the generation of the waves, namely Resonance and disintegration of interfacial tides, Generation of interfacial tides by impinging, remotely generated internal tidal beams and for geometrically focused and amplified internal tidal beams. Tide analysis based on tide stations data and barotropic tide model in the Red Sea shows that tide is indeed very weak in the centre part of the Red Sea, but it is relatively strong in the northern and southern parts (reaching up to 66 cm/s). Together with extreme steep slopes along the deep trench, it provides favourable conditions for the generation of internal solitary in the southern Red Sea. To investigate the generation mechanisms and study the evolution of the internal waves in the off-shelf region of the southern Red Sea we have implemented a 2-D, high-resolution and non-hydrostatic configuration of the MIT general circulation model (MITgcm). Our simulations reproduce well that the generation process of the internal solitary waves. Analysis of the model's output suggests that the interaction between the topography and tidal flow with the nonlinear effect is the main mechanism behind the generation of the internal solitary waves. Sensitivity experiments suggest that neither tidal beam nor the resonance effect of the topography is important factor in this process.

Sediment suspension and the dynamic mechanism during storms in the Yellow River Delta.

PubMed

Bian, Shuhua; Hu, Zjian; Liu, Jianqiang; Zhu, Zichen

2016-12-01

The suspension and hydrodynamic characteristics of the Yellow River Delta during storms were analyzed based on suspended samples obtained using automatic samplers during a storm event in the Yellow River Delta. Synchronous data for winds, waves, and tides were also collected from a nearby station. The results show that under wind speeds of 5-15 m/s and wave heights of 50-150 cm, the suspended content reached 5.7-49.6 kg/m 3 , which is 10-100 times higher than that under normal weather conditions. The medium diameter of suspended particles was 1.2-2.1 μm (8.9-9.7 Φ), which was approximately 1-2 Φ finer than that under normal weather conditions. During the early stages of the measurements, the sea level had risen by 50 cm owing to the storm, which was in addition to the tidal sea level change. We suggest that during the storms, the waves strengthened and the storm-induced sea level change, which was combined with tidal currents moving in the same direction, produced high-speed currents. This overcame the cohesive forces among the fine sediment particles and suspended a large amount of sediment. As a result, the suspended content increased markedly and the suspended particle size became finer. This explains the intense siltation and erosion of the Yellow River Delta during storms.

Tidal Signals In GOCE Measurements And Time-GCM

NASA Astrophysics Data System (ADS)

Hausler, K.; Hagan, M. E.; Lu, G.; Doornbos, E.; Bruinsma, S.; Forbes, J. M.

2013-12-01

In this paper we investigate tidal signatures in GOCE measurements during 15-24 November 2009 and complementary simulations with the Thermosphere-Ionosphere- Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). The TIME-GCM simulations are driven by inputs that represent the prevailing solar and geomagnetic conditions along with tidal and planetary waves applied at the lower boundary (ca. 30km). For this pilot study, the resultant TIME-GCM densities are analyzed in two ways: 1) we use results along the GOCE orbital track, to calculate ascending/descending orbit longitude- latitude density difference and sum maps for direct comparison with the GOCE diagnostics, and 2) we conduct a complete analysis of TIME-GCM results to unambiguously characterize the simulated atmospheric tides and to attribute the observed longitude variations to specific tidal components. TIME-GCM captures some but not all of the observed longitudinal variability. The good data- model agreement for wave-2, wave-3, and wave-4 suggests that thermospheric impacts can be attributed to the DE1, DE2, DE3, S0, SE1, and SE2 tides. Discrepancies between TIME-GCM and GOCE results are most prominent in the wave-1 variations, and suggest that further refinement of the lower boundary forcing is necessary before we extend our analysis and interpretation to densities associated with the remainder of the GOCE mission.

Remote Sensing Characterization of Two-dimensional Wave Forcing in the Surf Zone

NASA Astrophysics Data System (ADS)

Carini, R. J.; Chickadel, C. C.; Jessup, A. T.

2016-02-01

In the surf zone, breaking waves drive longshore currents, transport sediment, shape bathymetry, and enhance air-sea gas and particle exchange. Furthermore, wave group forcing influences the generation and duration of rip currents. Wave breaking exhibits large gradients in space and time, making it challenging to measure in situ. Remote sensing technologies, specifically thermal infrared (IR) imagery, can provide detailed spatial and temporal measurements of wave breaking at the water surface. We construct two-dimensional maps of active wave breaking from IR imagery collected during the Surf Zone Optics Experiment in September 2010 at the US Army Corps of Engineers' Field Research Facility in Duck, NC. For each breaker identified in the camera's field of view, the crest-perpendicular length of the aerated breaking region (roller length) and wave direction are estimated and used to compute the wave energy dissipation rate. The resultant dissipation rate maps are analyzed over different time scales: peak wave period, infragravity wave period, and tidal wave period. For each time scale, spatial maps of wave breaking are used to characterize wave forcing in the surf zone for a variety of wave conditions. The following phenomena are examined: (1) wave dissipation rates over the bar (location of most intense breaking) have increased variance in infragravity wave frequencies, which are different from the peak frequency of the incoming wave field and different from the wave forcing variability at the shoreline, and (2) wave forcing has a wider spatial distribution during low tide than during high tide due to depth-limited breaking over the barred bathymetry. Future work will investigate the response of the variability in wave setup, longshore currents and rip currents, to the variability in wave forcing in the surf zone.

The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations

NASA Astrophysics Data System (ADS)

Lühr, H.; Manoj, C.

2013-08-01

Based on 10 yr of magnetic field measurements by the CHAMP satellite we draw a detailed picture of the equatorial electrojet (EEJ) tidal variations. For the first time the complete EEJ spectrum related to average solar tides has been compiled. A large fraction of the resulting spectrum is related to the switch on/off of the EEJ between day and night. This effect has carefully been considered when interpreting the results. As expected, largest amplitudes are caused by the migrating tides representing the mean diurnal variation. Higher harmonics of the daily variations show a 1/f fall-off in amplitude. Such a spectrum is required to represent the vanishing of the EEJ current at night. The migrating tidal signal exhibits a distinct annual variation with large amplitudes during December solstice and equinox seasons but a depression by a factor of 1.7 around June-July. A rich spectrum of non-migrating tidal effects is deduced. Most prominent is the four-peaked longitudinal pattern around August. Almost 90% of the structure can be attributed to the diurnal eastward-propagating tide DE3. In addition the westward-propagating DW5 is contributing to wave-4. The second-largest non-migrating tide is the semi-diurnal SW4 around December solstice. It causes a wave-2 feature in satellite observations. The three-peaked longitudinal pattern, often quoted as typical for the December season, is significantly weaker. During the months around May-June a prominent wave-1 feature appears. To first order it represents a stationary planetary wave SPW1 which causes an intensification of the EEJ at western longitudes beyond 60° W and a weakening over Africa/India. In addition, a prominent ter-diurnal non-migrating tide TW4 causes the EEJ to peak later, at hours past 14:00 local time in the western sector. A particularly interesting non-migrating tide is the semi-diurnal SW3. It causes largest EEJ amplitudes from October through December. This tidal component shows a strong dependence on solar flux level with increasing amplitudes towards solar maximum. We are not aware of any previous studies mentioning this behaviour of SW3. The main focus of this study is to present the observed EEJ spectrum and its relation to tidal driving. For several of the identified spectral components we cannot offer convincing explanations for the generation mechanisms.

Forcing a three-dimensional, hydrostatic, primitive-equation model for application in the surf zone: 2. Application to DUCK94

NASA Astrophysics Data System (ADS)

Newberger, P. A.; Allen, J. S.

2007-08-01

A three-dimensional primitive-equation model for application to the nearshore surf zone has been developed. This model, an extension of the Princeton Ocean Model (POM), predicts the wave-averaged circulation forced by breaking waves. All of the features of the original POM are retained in the extended model so that applications can be made to regions where breaking waves, stratification, rotation, and wind stress make significant contributions to the flow behavior. In this study we examine the effects of breaking waves and wind stress. The nearshore POM circulation model is embedded within the NearCom community model and is coupled with a wave model. This combined modeling system is applied to the nearshore surf zone off Duck, North Carolina, during the DUCK94 field experiment of October 1994. Model results are compared to observations from this experiment, and the effects of parameter choices are examined. A process study examining the effects of tidal depth variation on depth-dependent wave-averaged currents is carried out. With identical offshore wave conditions and model parameters, the strength and spatial structure of the undertow and of the alongshore current vary systematically with water depth. Some three-dimensional solutions show the development of shear instabilities of the alongshore current. Inclusion of wave-current interactions makes an appreciable difference in the characteristics of the instability.

Coupling of wave and circulation models in coastal-ocean predicting systems: A case study for the German Bight

NASA Astrophysics Data System (ADS)

Staneva, Joanna; Wahle, Kathrin

2015-04-01

This study addresses the coupling between wind wave and circulation models on the example of the German Bight and its coastal area called the Wadden Sea (the area between the barrier islands and the coast). This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales. The uncertainties in most of the presently used models result from the nonlinear feedback between strong tidal currents and wind-waves, which can no longer be ignored, in particular in the coastal zone where its role seems to be dominant. A nested modelling system is used in the Helmholtz-Zentrum Geesthacht to producing reliable now- and short-term forecasts of ocean state variables, including wind waves and hydrodynamics. In this study we present analysis of wave and hydrographic observations, as well as the results of numerical simulations. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecasting system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and SST simulations are investigated considering wave-dependent stress and wave breaking parameterization during extreme events, e.g. hurricane Xavier in December, 2013. Also the effect which the circulation exerts on the wind waves is tested for the coastal areas using different parameterizations. The improved skill resulting from the new developments in the forecasting system, in particular during extreme events, justifies further enhancements of the coastal pre-operational system for the North Sea and German Bight.

Marine Renewable Energy: Resource Characterization and Physical Effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhaoqing; Copping, Andrea E.

This complete reference to marine renewable energy covers aspects of resource characterization and physical effects of harvesting the ocean’s vast and powerful resources—from wave and tidal stream to ocean current energy. Experts in each of these areas contribute their insights to provide a cohesive overview of the marine renewable energy spectrum based on theoretical, numerical modeling, and field-measurement approaches.

Tidal residual current and its role in the mean flow on the Changjiang Bank

NASA Astrophysics Data System (ADS)

Xuan, Jiliang; Yang, Zhaoqing; Huang, Daji; Wang, Taiping; Zhou, Feng

2016-02-01

The tidal residual current may play an important role in the mean flow in the Changjiang Bank region, in addition to other residual currents, such as the Taiwan Warm Current, the Yellow Sea Coastal Current, and the Yellow Sea Warm Current. In this paper, a detailed structure of the tidal residual current, in particular the meso-scale eddies, in the Changjiang Bank region is observed from model simulations, and its role in the mean flow is quantified using the well-validated Finite Volume Coastal Ocean Model. The tidal residual current in the Changjiang Bank region consists of two components: an anticyclonic regional-scale tidal residual circulation around the edge of the Changjiang Bank and some cyclonic meso-scale tidal residual eddies across the Changjiang Bank. The meso-scale tidal residual eddies occur across the Changjiang Bank and contribute to the regional-scale tidal residual circulation offshore at the northwest boundary and on the northeast edge of the Changjiang Bank, southeastward along the 50 m isobath. Tidal rectification is the major mechanism causing the tidal residual current to flow along the isobaths. Both components of the tidal residual current have significant effects on the mean flow. A comparison between the tidal residual current and the mean flow indicates that the contribution of the tidal residual current to the mean flow is greater than 50%.

Atmospheric thermal tides and planetary spin. I. The complex interplay between stratification and rotation

NASA Astrophysics Data System (ADS)

Auclair-Desrotour, P.; Mathis, S.; Laskar, J.

2018-02-01

Context. Thermal atmospheric tides can torque telluric planets away from spin-orbit synchronous rotation, as observed in the case of Venus. They thus participate in determining the possible climates and general circulations of the atmospheres of these planets. Aims: The thermal tidal torque exerted on an atmosphere depends on its internal structure and rotation and on the tidal frequency. Particularly, it strongly varies with the convective stability of the entropy stratification. This dependence has to be characterized to constrain and predict the rotational properties of observed telluric exoplanets. Moreover, it is necessary to validate the approximations used in global modelings such as the traditional approximation, which is used to obtain separable solutions for tidal waves. Methods: We wrote the equations governing the dynamics of thermal tides in a local vertically stratified section of a rotating planetary atmosphere by taking into account the effects of the complete Coriolis acceleration on tidal waves. This allowed us to analytically derive the tidal torque and the tidally dissipated energy, which we used to discuss the possible regimes of tidal dissipation and to examine the key role played by stratification. Results: In agreement with early studies, we find that the frequency dependence of the thermal atmospheric tidal torque in the vicinity of synchronization can be approximated by a Maxwell model. This behavior corresponds to weakly stably stratified or convective fluid layers, as observed previously. A strong stable stratification allows gravity waves to propagate, and makes the tidal torque negligible. The transition is continuous between these two regimes. The traditional approximation appears to be valid in thin atmospheres and in regimes where the rotation frequency is dominated by the forcing or the buoyancy frequencies. Conclusions: Depending on the stability of their atmospheres with respect to convection, observed exoplanets can be tidally driven toward synchronous or asynchronous final rotation rates. The domain of applicability of the traditional approximation is rigorously constrained by calculations.

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait

NASA Astrophysics Data System (ADS)

Droghei, R.; Falcini, F.; Casalbore, D.; Martorelli, E.; Mosetti, R.; Sannino, G.; Santoleri, R.; Chiocci, F. L.

2016-11-01

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Fine-scale hydrodynamics influence the spatio-temporal distribution of harbour porpoises at a coastal hotspot

NASA Astrophysics Data System (ADS)

Jones, A. R.; Hosegood, P.; Wynn, R. B.; De Boer, M. N.; Butler-Cowdry, S.; Embling, C. B.

2014-11-01

The coastal Runnelstone Reef, off southwest Cornwall (UK), is characterised by complex topography and strong tidal flows and is a known high-density site for harbour porpoise (Phocoena phocoena); a European protected species. Using a multidisciplinary dataset including: porpoise sightings from a multi-year land-based survey, Acoustic Doppler Current Profiling (ADCP), vertical profiling of water properties and high-resolution bathymetry; we investigate how interactions between tidal flow and topography drive the fine-scale porpoise spatio-temporal distribution at the site. Porpoise sightings were distributed non-uniformly within the survey area with highest sighting density recorded in areas with steep slopes and moderate depths. Greater numbers of sightings were recorded during strong westward (ebbing) tidal flows compared to strong eastward (flooding) flows and slack water periods. ADCP and Conductivity Temperature Depth (CTD) data identified fine-scale hydrodynamic features, associated with cross-reef tidal flows in the sections of the survey area with the highest recorded densities of porpoises. We observed layered, vertically sheared flows that were susceptible to the generation of turbulence by shear instability. Additionally, the intense, oscillatory near surface currents led to hydraulically controlled flow that transitioned from subcritical to supercritical conditions; indicating that highly turbulent and energetic hydraulic jumps were generated along the eastern and western slopes of the reef. The depression and release of isopycnals in the lee of the reef during cross-reef flows revealed that the flow released lee waves during upslope currents at specific phases of the tidal cycle when the highest sighting rates were recorded. The results of this unique, fine-scale field study provide new insights into specific hydrodynamic features, produced through tidal forcing, that may be important for creating predictable foraging opportunities for porpoises at a local scale. Information on the functional mechanisms linking porpoise distribution to static and dynamic physical habitat variables is extremely valuable to the monitoring and management of the species within the context of European conservation policies and marine renewable energy infrastructure development.

A Study of Stranding of Juvenile Salmon by Ship Wakes Along the Lower Columbia River Using a Before-and-After Design: Before-Phase Results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearson, Walter H.; Skalski, J R.; Sobocinski, Kathryn L.

2006-02-01

Ship wakes produced by deep-draft vessels transiting the lower Columbia River have been observed to cause stranding of juvenile salmon. Proposed deepening of the Columbia River navigation channel has raised concerns about the potential impact of the deepening project on juvenile salmon stranding. The Portland District of the U.S. Army Corps of Engineers requested that the Pacific Northwest National Laboratory design and conduct a study to assess stranding impacts that may be associated with channel deepening. The basic study design was a multivariate analysis of covariance of field observations and measurements under a statistical design for a before and aftermore » impact comparison. We have summarized field activities and statistical analyses for the ?before? component of the study here. Stranding occurred at all three sampling sites and during all three sampling seasons (Summer 2004, Winter 2005, and Spring 2005), for a total of 46 stranding events during 126 observed vessel passages. The highest occurrence of stranding occurred at Barlow Point, WA, where 53% of the observed events resulted in stranding. Other sites included Sauvie Island, OR (37%) and County Line Park, WA (15%). To develop an appropriate impact assessment model that accounted for relevant covariates, regression analyses were conducted to determine the relationships between stranding probability and other factors. Nineteen independent variables were considered as potential factors affecting the incidence of juvenile salmon stranding, including tidal stage, tidal height, river flow, current velocity, ship type, ship direction, ship condition (loaded/unloaded), ship speed, ship size, and a proxy variable for ship kinetic energy. In addition to the ambient and ship characteristics listed above, site, season, and fish density were also considered. Although no single factor appears as the primary factor for stranding, statistical analyses of the covariates resulted in the following equations: (1) Stranding Probability {approx} Location + Kinetic Energy Proxy + Tidal Height + Salmonid Density + Kinetic energy proxy ? Tidal Height + Tidal Height x Salmonid Density. (2) Stranding Probability {approx} Location + Total Wave Distance + Salmonid Density Index. (3) Log(Total Wave Height) {approx} Ship Block + Tidal Height + Location + Ship Speed. (4) Log(Total Wave Excursion Across the Beach) {approx} Location + Kinetic Energy Proxy + Tidal Height The above equations form the basis for a conceptual model of the factors leading to salmon stranding. The equations also form the basis for an approach for assessing impacts of dredging under the before/after study design.« less

Experiments on topographies lacking tidal conversion

NASA Astrophysics Data System (ADS)

Maas, Leo; Paci, Alexandre; Yuan, Bing

2015-11-01

In a stratified sea, internal tides are supposedly generated when the tide passes over irregular topography. It has been shown that for any given frequency in the internal wave band there are an infinite number of exceptions to this rule of thumb. This ``stealth-like'' property of the topography is due to a subtle annihilation of the internal waves generated during the surface tide's passage over the irregular bottom. We here demonstrate this in a lab-experiment. However, for any such topography, subsequently changing the surface tide's frequency does lead to tidal conversion. The upshot of this is that a tidal wave passing over an irregular bottom is for a substantial part trapped to this irregularity, and only partly converted into freely propagating internal tides. Financially supported by the European Community's 7th Framework Programme HYDRALAB IV.

Circulation and fjord-shelf exchange during the ice-covered period in Young Sound-Tyrolerfjord, Northeast Greenland (74°N)

NASA Astrophysics Data System (ADS)

Boone, W.; Rysgaard, S.; Kirillov, S.; Dmitrenko, I.; Bendtsen, J.; Mortensen, J.; Meire, L.; Petrusevich, V.; Barber, D. G.

2017-07-01

Fjords around Greenland connect the Greenland Ice Sheet to the ocean and their hydrography and circulation are determined by the interplay between atmospheric forcing, runoff, topography, fjord-shelf exchange, tides, waves, and seasonal growth and melt of sea ice. Limited knowledge exists on circulation in high-Arctic fjords, particularly those not impacted by tidewater glaciers, and especially during winter, when they are covered with sea-ice and freshwater input is low. Here, we present and analyze seasonal observations of circulation, hydrography and cross-sill exchange of the Young Sound-Tyrolerfjord system (74°N) in Northeast Greenland. Distinct seasonal circulation phases are identified and related to polynya activity, meltwater and inflow of coastal water masses. Renewal of basin water in the fjord is a relatively slow process that modifies the fjord water masses on a seasonal timescale. By the end of winter, there is two-layer circulation, with outflow in the upper 45 m and inflow extending down to approximately 150 m. Tidal analysis showed that tidal currents above the sill were almost barotropic and dominated by the M2 tidal constituent (0.26 m s-1), and that residual currents (∼0.02 m s-1) were relatively small during the ice-covered period. Tidal pumping, a tidally driven fjord-shelf exchange mechanism, drives a salt flux that is estimated to range between 145 kg s-1 and 603 kg s-1. Extrapolation of these values over the ice-covered period indicates that tidal pumping is likely a major source of dense water and driver of fjord circulation during the ice-covered period.

Tidal impact on geophysical fields registed in GPO "Mikhnevo" area

NASA Astrophysics Data System (ADS)

Vinogradov, Evgeny; Besedina, Alina; Gorbunova, Ella

2013-04-01

Geophysical observatory "Mikhnevo" is situated in the centre of Russian Plate and characterized with stable response to lunisolar tides. Since February 2008, regular precision measurements of groundwater level are carried out in a measurement well synchronously with atmospheric pressure measurements (sampling interval is 1 s, the measurement accuracy is 0.1 mm for the level and 0.1 gPa for atmospheric pressure). According to the results of hydrogeological sampling, the pressure head in the aquifer under study is 8.1 m, its transmissivity is 3.0 m2/day, hydraulic conductivity was 0.13 m/day, the pressure conductivity factor and elastic water yield are 1.3 × 104 m2/day and 2.3 × 10-4, respectively. Using flow measurements and telemetry of the open part of bore hole, major intervals of water inflow were detected at depths of 92-94 m and 99-100 m. Rock transmissivity in the fissure-conducting zone increases to 5.0 m2/day. Based on tidal component analysis in the filtered hydrogeological data, five main kinds of tidal waves were extracted (?1, ?2, Q1, ?1 and 2). STS-2 and KSESh-R seismometers registration range extension made it possible to extract tidal waves from Z-component of ground displacement. Similar methodology of data processing was used for tides analysis in hydrogeological, seismic and barometric data. It should be noted that barometric component extracted from water level variations can, in some cases, lead to misrepresentation of the data in frequency range under consideration. That is why two variants of data were analysed - with included and excluded barometric component. To extract tides from water level variations, long-period and barometric components were excluded from original precise monitoring datum. Data series obtained in this way were used for monthly spectrum realization, which, in turn, allowed finding out amplitudes of main tidal waves ?1, ?1 and 2. The most significant luni-solar ?1 wave annual variations cycle correlates with hydraulic head. Maximum amplitudes of ?1 wave for the whole 4 year observation period are observed then the ground-water level is high. Variation range of ?1 wave amplitude is stable and reaches 2.9 mm per year. Most significant variations take place in spring-summer period. Main lunar waves amplitude variations do not exceed 1.1 mm. The phase shift increase between luni-solar tides response in seismic and hydrogeological data was found. Diurnal O1 wave variations analysis should be done with barometric component excluded datum because of amplitude difference. During period under consideration M2 and K1 waves amplitudes are comparable and about 4.1 mm, O1 amplitude is on it minimum about 3.7 mm. Maximum diurnal and semi-diurnal wave amplitudes of water level variations confine with minimum values of luni-solar attraction. On the contrary on the same periods we can see decrease of ground displacement amplitudes as a result of tidal forces. Main tidal waves were extracted from atmospheric pressure datum too. Luni-solar K1 wave has the most amplitude there and exceeds O1 and M2 values 5-7 times.

Currents and Mixing in the San Lorenzo Overflow, Northern Gulf of California

NASA Astrophysics Data System (ADS)

Rosas-Villegas, Froylán.; López, Manuel; Candela, Julio

2018-02-01

The main properties of the San Lorenzo (SL) overflow are studied, using data from two nonsimultaneous ADCP moorings (located at the sill, and 5 km downstream), as well as CTD and LADCP profiles. Strong tidal currents at the sill modulate the overflow, which is not shut down during the neaps. At the downstream site, the largest flood currents are associated with colder water advected from the sill, flowing downslope, and creating an asymmetry in the semidiurnal tidal cycle. The overflow introduces a significant fortnightly harmonic at the downstream site, and delays the M2 tidal currents for more than an hour with respect to the currents at the sill. The overflow mixes with the overlying water by entrainment during its supercritical stage, reaching near-bottom velocities as high as 1.5 ms-1 and an estimated mean transport of 0.11 Sv; almost twice that estimated at the sill for the same period of the year. Estimated Froude numbers during spring tides suggest the development of an internal hydraulic jump. After relaxation of the maximum downstream currents, high-frequency temperature fluctuations, likely linked to upstream traveling waves, are consistently observed. Direct estimations of the turbulent dissipation rates were used to compute diapycnal diffusivity (Kρ) profiles. Mean estimates of Kρ, as high as 5.5 × 10-2 m2s-1, show that shear at the interface is the most significant source of cross-isopycnal mixing along the SL overflow during ebb tides.

Long-term Global Morphology of Gravity Wave Activity Using UARS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Jackman, C. (Technical Monitor)

2000-01-01

An extensive body of research this quarter is documented. Further methodical analysis of temperature residuals in Cryogenic Limb Array Etalon Spectrometer (CLAES) Version 8 level 3AT data show signatures during December 1992 at middle and high northern latitudes that, when compared to Naval Research Laboratory/Mountain Wave Forecast Model (NRL)/(MWFM) mountain wave hindcasts, reveal evidence of long mountain waves in these data over Eurasia, Greenland, Scandinavia and North America. The explicit detection of gravity waves in limb-scanned Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) temperatures is modeled at length, to derive visibility functions. These insights are used to convert CRISTA gravity wave temperature residuals into data that more closely resemble gravity wave fluctuations detected in data from other satellite instruments, such as Microwave Limb Sounder (MLS), Limb Infrared Monitor of the Stratosphere (LIMS) and Global Positioning System/Meteorology (GPS)/(MET). Finally, newly issued mesospheric temperatures from inversion of CRISTA 15gin emissions are analyzed using a new method that uses separate Kalman fits to the ascending and descending node data. This allows us to study global gravity wave amplitudes at two local times, 12 hours apart. In the equatorial mesosphere, where a large diurnal tidal temperature signal exists, we see modulations of gravity wave activity that are consistent with gravity wave-tidal interactions produced by tidal temperature variability.

Ocean-Wave Dynamics Analysis during Hurricane Ida and Norida Using a Fully Coupled Modeling System

NASA Astrophysics Data System (ADS)

Olabarrieta, M.; Warner, J. C.; Armstrong, B. N.

2010-12-01

Extreme storms, such as hurricanes and extratropical storms play a dominant role in shaping the beaches of the East and Gulf Coasts of the United States. Future tropical depressions will be more intense than in the present climate (Assessment Report of IPCC, 2007) and therefore coastal areas are likely to become more susceptible to their effects. The major damage caused by these extreme events is associated with the duration of the storm, storm intensity, waves, and the total water levels reached during the storm. Numerical models provide a useful approach to study the spatial and temporal distribution of these parameters. However, the correct estimation of the total water levels and wind wave heights through numerical modeling requires accurate representation of the air-sea interface dynamics. These processes are highly complex due to the variable interactions between winds, ocean waves and currents near the sea surface. In the present research we use the COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) modeling system (Warner et al., 2010) to address the key role of the atmosphere-ocean-wave interactions during Hurricane Ida and its posterior evolution to NorIda, November 2009. This northeastern storm was one of the most costly in the past two decades and likely in the top five of the past century. One interesting aspect of the considered period is that it includes two very different atmospheric extreme conditions, a hurricane and a northeastern storm, developed in regions with very different oceanographic characteristics. By performing a suite of numerical runs we are able to isolate the effect of the interaction terms between the atmosphere (WRF model), the ocean (ROMS model) and the wave propagation and generation model (SWAN). Special attention is given to the role of the ocean surface roughness and high resolution SST fields on the atmospheric boundary layers dynamics and consequently these effects on the wind wave generation, surface currents and storm surge. The effects of ocean currents on wind wave generation and propagations are also analyzed. The model results are compared to different data sources, including GOES satellite infrared data, JASON-1 and JASON-2 altimeter data, CODAR measurements, and wave and tidal information from the NDBC and the National Tidal Database respectively. The results identified that the inclusion of the ocean roughness on the atmospheric module greatly improves the wind intensity estimation and therefore also the wind waves and the storm surge amplitude. For example, during the passage of Ida through the Gulf of Mexico the wind speeds are reduced due to the wave induced ocean roughness, resulting in better agreement with the measured winds. During NorIda, the effect of the surface roughness changed the form and dimension of the main low pressure cell, affecting the intensity and direction of the winds. Three different ocean roughness closure models are analyzed, with the wave-age based closure model providing the best results. Ocean currents are also shown to affect wave spectral characteristics through the generation and propagation processes. Changes within 15% on the significant wave height are detected in areas affected by the main oceanic currents: the Gulf Stream and the Loop Current.

Tidal residual current and its role in the mean flow on the Changjiang Bank

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xuan, Jiliang; Yang, Zhaoqing; Huang, Daji

Tidal residual current may play an important role in the mean flow in the Changjiang Bank region, in addition to other residual currents, such as the Taiwan Warm Current, the Yellow Sea Coastal Current, and the Yellow Sea Warm Current. In this paper, a detailed structure of the tidal residual current, in particular the meso-scale eddies, in the Changjiang Bank region is observed from model simulations, and its role in the mean flow is quantified using the well-validated Finite Volume Coastal Ocean Model). The tidal residual current in the Changjiang Bank region consists of two components: an anticyclonic regional-scale tidalmore » residual circulation around the edge of the Changjiang Bank and some cyclonic meso-scale tidal residual eddies across the Changjiang Bank. The meso-scale tidal residual eddies occur across the Changjiang Bank and contribute to the regional-scale tidal residual circulation offshore at the northwest boundary and at the northeast edge of the Changjiang Bank, southeastward along the 50 m isobath. Tidal rectification is the major mechanism causing the tidal residual current to flow along the isobaths. Both components of the tidal residual current have significant effects on the mean flow. A comparison between the tidal residual current and the mean flow indicates that the contribution of the tidal residual current to the mean flow is greater than 50%.« less

Extended I-Love relations for slowly rotating neutron stars

NASA Astrophysics Data System (ADS)

Gagnon-Bischoff, Jérémie; Green, Stephen R.; Landry, Philippe; Ortiz, Néstor

2018-03-01

Observations of gravitational waves from inspiralling neutron star binaries—such as GW170817—can be used to constrain the nuclear equation of state by placing bounds on stellar tidal deformability. For slowly rotating neutron stars, the response to a weak quadrupolar tidal field is characterized by four internal-structure-dependent constants called "Love numbers." The tidal Love numbers k2el and k2mag measure the tides raised by the gravitoelectric and gravitomagnetic components of the applied field, and the rotational-tidal Love numbers fo and ko measure those raised by couplings between the applied field and the neutron star spin. In this work, we compute these four Love numbers for perfect fluid neutron stars with realistic equations of state. We discover (nearly) equation-of-state independent relations between the rotational-tidal Love numbers and the moment of inertia, thereby extending the scope of I-Love-Q universality. We find that similar relations hold among the tidal and rotational-tidal Love numbers. These relations extend the applications of I-Love universality in gravitational-wave astronomy. As our findings differ from those reported in the literature, we derive general formulas for the rotational-tidal Love numbers in post-Newtonian theory and confirm numerically that they agree with our general-relativistic computations in the weak-field limit.

Small-scale open ocean currents have large effects on wind wave heights

NASA Astrophysics Data System (ADS)

Ardhuin, Fabrice; Gille, Sarah T.; Menemenlis, Dimitris; Rocha, Cesar B.; Rascle, Nicolas; Chapron, Bertrand; Gula, Jonathan; Molemaker, Jeroen

2017-06-01

Tidal currents and large-scale oceanic currents are known to modify ocean wave properties, causing extreme sea states that are a hazard to navigation. Recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies, fronts, and filaments at scales 10-100 km. Based on realistic numerical models, we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km, including important variations down to 10 km. Model results are consistent with wave height variations along satellite altimeter tracks, resolved at scales larger than 50 km. The spectrum of significant wave heights is found to be of the order of 70>>2/>(g2>>2>) times the current spectrum, where >> is the spatially averaged significant wave height, >> is the energy-averaged period, and g is the gravity acceleration. This variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing.