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22 pages, 11 figures, 1 table [EN] Good knowledge of the coastal circulation patterns is essential for a proper management of the coastline, especially in areas with a high anthropic pressure. In order to determine the main characteristics of the coastal currents in the Gulf of Urabá, the seasonal patterns of surface circulation were measured and analyzed during times of high and low rainfall along 6 km of coastline, between the Punta de Las Vacas and Punta Yarumal coastal spit systems, in the municipality of Turbo, Antioquia. These measurements were made with surface drifters, which were launched at different tide stages and tracked for time periods based on the semi-diurnal cycle. The in-situ measurements were analyzed alongside tide and wind data from a climatic station located near the gulf. The circulation patterns behaved differently depending on the season of the year. In the rainy season, with southerly winds, the drifters moved mainly towards the north while during the dry season, with northerly winds, all the drifters moved to the south. Although the circulation patterns showed a strong relationship with the tidal cycle and wind conditions, the Turbo and El Uno Bays modified some of the drifter’s paths [ES] Conocer los patrones de circulación costera es fundamental para gestionar adecuadamente la franja litoral, especialmente en áreas con alta presión antrópica. Con el objetivo de determinar las características de las corrientes costeras en el golfo de Urabá, se midieron y analizaron los patrones estacionales de circulación superficial durante las épocas de mucha y poca lluvia a lo largo de 6 km de costa, entre las espigas litorales de punta de Las Vacas y punta Yarumal del municipio de Turbo, Antioquia. Estas mediciones se realizaron con derivadores superficiales, que fueron lanzados en diversos estadios de la marea y rastreados durante periodos cercanos al ciclo semidiurno. Las mediciones in situ se analizaron considerando la evolución de la marea y los vientos observados en una estación climática ubicada cerca del golfo. Los patrones de circulación mostraron un comportamiento diferente durante las dos estaciones del año. La temporada de mucha lluvia, con vientos del sur, presentó trayectorias hacia el norte y la temporada de poca lluvia, con vientos del norte, las trayectorias fueron hacia el sur. Aunque los patrones de circulación mostraron una fuerte relación con la marea y el viento, las trayectorias de algunos derivadores se modificaron localmente por la presencia de geoformas como las bahías de Turbo y El Uno Part of this research was carried out within the framework of the project “Collaboration for the development of an oceanographic, atmospheric and environmental observatory project for the Gulfs of Darién and Urabá, Colombia”, reference COOPB20337, financed by the State Agency: Consejo Superior de Investigaciones Científicas, Spain (CSIC) With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Europa likely has an active surface ice shell producing numerous low-magnitude (

A setup of a two-dimensional hydrodynamic model based on Delft3D modeling system for the coastal waters of Jeddah is described. Sensitivity tests of both numerical and physical parameters defined in the model and validation of the numerical model are also described. The model was forced by major tidal constituents along the open boundary. The performance of the model was evaluated using available water level observations at four sites along Jeddah coast. The simulated tidal elevations showed a very good matching with the observed tidal elevations. The spring and neap tidal cycle are reproduced by the model with good degree. Statistical analysis showed that RMSD error ranges between 0.001 and 0.17 m, while the MAD values vary between 0.02 and 0.08 m. Comparison of simulated and observed amplitudes and phases of the main tidal components also showed a good agreement. The predicted tide-induced current flooding and ebbing features during spring and neap tides were analyzed. The model suggests that the flow in the region is weak where the strengths of the currents increase towards the shallow areas.

The intertidal beach profile provides coastal engineers and managers with a good indication of the current state of a sandy coastline, however regular beach profile measurements are time consuming and expensive to obtain using conventional surveying methods. The potential to reconstruct the intertidal beach profile from measurements of reflected waves is tested here using three field datasets covering a different range of hydro-morphological conditions from dissipative, to reflective. The swash is found to behave as a low-pass filter on reflected waves, with a cut-off frequency that primarily depends on the swash slope. An agreement is found between video-derived swash spectrum saturation tail and the shortest reflected waves, computed from deep water directional wave measurements. By integrating this swash slope over a tidal cycle, the shape of the intertidal beach profile can be reconstructed. Our results clearly show the potential of such method to estimate complex intertidal beach profile, such as double-slope beaches.

© 2019 Elsevier B.V. Intertidal flats are shallow-water environments that undergo cyclical variations in water depth, leading to a frequent occurrence of extremely shallow water stages (ESWS; water depths 0.2 m), and the rate of change was an order of magnitude faster than during RDWS. This larger and faster bed-level change occurred even though the ESWS duration only accounted for 10% of the entire tidal cycle. This result occurred because the bed shear stress due to combined current–wave action during ESWS, was, on average, two times higher than during RDWS at the flood stage causing more extensive erosion. Whereas during the ebb stage, this shear stress during ESWS was only half of that during RDWS resulting in greater accretion. The main implications of these results are that, because ESWS occur frequently (twice every tide) and are associated with large bed shear stress and bed-level changes, these conditions are likely to play an important role in morphological changes of intertidal flats. Our study shows that ESWS have a key influence on intertidal flat hydrodynamics and sediment dynamics. Thus our results are the basis for an improved understanding of the coastal morphodynamic processes on intertidal flats.

Safaga and Qusseir are two important harbours on the Egyptian Proper Red Sea coast. To the best of the authors’ knowledge, this is the first work to describe the sea level characteristics at these two ports. The study is based on hourly sea level records over 3 years (2012–2014). There are no missed data at Qusseir site, but Safaga dataset missed 25% of records (April–December 2014). The hourly water level ranged between 0.02 m and 1.70 m at Safaga and between 0.04 m and 1.03 m at Qusseir, with a mean sea level (MSL) of 0.56 m and 0.50 m at the two Harbours, respectively. The T_TIDE package was used to produce astronomical and residual elevations at the two Harbours. Results revealed that the two Harbours examine explicit semidiurnal tidal cycle, with a bit higher astronomical amplitudes in Safaga. Moreover, the two sites exhibit almost the same seasonal sea level trend with very slight differences. The monthly mean levels at the two Harbours are always below their averages except during the summer months. The principal features of the semidiurnal tides indicated a ratio of 1.3 and 1.5 between spring and neap ranges at Safaga and Qusseir, respectively. The most pronounced sea level range at Safaga Harbour was 0.50 m, while it was 0.60 m at Qusseir Harbour. The astronomical elevations fluctuated between − 0.55 m and + 0.71 m and between − 0.47 m and + 0.53 m in Safaga and Qusseir Harbours, respectively.

(IF 2.98; Q1); International audience; Modelling three-dimensional wave-current-turbulence interactions in extreme tidal environments is still challenging and necessary for the development of the tidal industry, particularly for the dimensioning of tidal converters. Following this objective, we focus our study on the Alderney Race (France) where the strongest tidal current in Western Europe and various sea states occur. Due to the strong tidal current at this location, wave-current interactions were poorly studied by the past. Therefore, we propose to assess the impacts of wave-current interactions in Alderney Race by the use of a 3D fully-coupled wave-current numerical model and in-situ measurements. The following wave-current interactions were observed : i) Stokes drift e ects inducing an increase/decrease in the current depending on the angle between waves and current, ii) wave enhancement of the bottom friction reducing the tidal current, iii) refraction of waves by the current, generating changes in waves directions, and iv) wave breaking ascribed to tidal current. The impact of such interactions were maximal near the reverse event ( 1h30) and for a weak/medium tidal range. A non-stationary time delay, varying within a same tidal cycle, was noted at both locations, which is reduced by including the local wind e ects and by adjusting the bottom stress formulation. This study shows that wave-current interactions play a non-negligible role in Alderney Race and that they need to consider by the tidal industry.

Local scour around pile foundations is a major factor affecting the foundation stability in ocean engineering. A series of experiments has been conducted to study the time development of scour around pile groups under the unidirectional and tidal currents. 49 cylindrical model piles were arranged in a typical dumbbell-shaped configuration, and 20 micro-cameras as well as a 3D laser scanner were used to capture the local scour topography. In the unidirectional current test, the scour pit was spoon-shaped, and the maximum scour depth was located in the central part of upstream pile group. In the tidal tests, two similar shallow scour pits existed in the upstream and downstream pile group. During the initial stage of tide-induced local scour, the increase of scour depth was similar to that under unidirectional current. But, the repetitive scour and backfill process led to obvious fluctuations of scour depth, especially for the piles at the rear of upstream pile group and in the front of downstream pile group. It was found that the tidal cycle number had obvious effect on the scour depth development. The final scour depth after sufficient tidal cycles could reach up to 77.1% of the maximum scour depth under unidirectional current.

Understanding erosion and accretion dynamics during an entire tidal cycle is important for assessing their impacts on the habitats of biological communities and the long-term morphological evolution of intertidal mudflats. However, previous studies often omitted erosion and accretion during very shallow-water stages (VSWS, water depths 0.2 m (i.e., probe submerged) are considered. These findings suggest that the magnitude of bed-level changes during VSWS should not be neglected when modeling morphodynamic processes. Our results are useful in understanding the mechanisms of micro-topography formation and destruction that often occur at VSWS, and also improve our understanding and modeling ability of coastal morphological changes.

Characteristics and formation of the tidal shear front off the Yellow River Mouth had been previously studied based on observations and models. However, its long-term variability and thus related mechanisms have not been investigated. In this study, a three-dimensional hydrodynamic model was used to examine the long-term evolution on the location, propagation, and magnitude (length, duration, and shear strength) of the tidal shear front from 1976 to 1996. Over the 20 years, a peninsula of about 27 km long and 7 km wide (above the high water line) was formed off the new river mouth, while the coastline retreated by 5–10 km, and the water depths increased by about 2 m in the north (the abandoned river mouth). Results also show that for the period of each flood and ebb tidal cycle, the tidal shear front originated in the north of the delta, then propagated southeastwards and finally disappeared at the south of the river mouth. During the two decades, the front had an obvious shoreward movement, and its duration within a tidal cycle increased slightly. Furthermore, the length of the front decreased, while the shear strength of the front increased. The propagation of the front was determined by flood and ebb process in the delta, where both of them were from north to south due to tidal phase distribution. Long-term characteristic variations of the front were mainly caused by morphology change, which had a significant influence on the tidal current gradient and the location of maximum bottom stress gradient area. The morphology change also had a slight impact on the tidal current phase in the front area, which may have caused the slight duration variation of the front.

This research quantifies the rate and volume of oil and gas released from two natural seep sites in the Gulf of Mexico: lease blocks GC600 (1200 m depth) and MC118 (850 m depth). Our objectives were to determine variability in release rates and bubble size at five individual vents and to investigate the effects of tidal fluctuations on bubble release. Observations with autonomous video cameras captured the formation of individual bubbles as they were released through partially exposed deposits of gas hydrate. Image processing techniques determined bubble type (oily, gaseous, and mixed: oily and gaseous), size distribution, release rate, and temporal variations (observation intervals ranged from 3 h to 26 d). A semi-automatic bubble counting algorithm was developed to analyze bubble count and release rates from video data. This method is suitable for discrete vents with small bubble streams commonly seen at seeps and is adaptable to multiple in situ set-ups. Two vents at GC600 (Birthday Candles 1 and Birthday Candles 2) were analyzed. They released oily bubbles with an average diameter of 5.0 mm at a rate of 4.7 bubbles s−1, and 1.3 bubbles s−1, respectively. Approximately 1 km away, within the GC600 seep site, two more vents (Mega Plume 1 and Mega Plume 2) were analyzed. These vents released a mixture of oily and gaseous bubbles with an average diameter of 3.9 mm at a rate of 49 bubbles s−1, and 81 bubbles s−1, respectively. The fifth vent at MC118 (Rudyville) released gaseous bubbles with an average diameter of 3.0 mm at a rate of 127 bubbles s−1. Pressure records at Mega Plume and Rudyville showed a diurnal tidal cycle (24.5 h). Rudyville was the only vent that demonstrated any positive correlation (ρ = 0.60) to the 24.5 h diurnal tidal cycle. However, these observations were not conclusive regarding tidal effects on bubble release.

In recent years, the application of large-scale beach nourishments has been discussed, with the Sand Motor in the Netherlands as the first real-world example. Such protruding beach nourishments have an impact on tidal currents, potentially leading to tidal flow separation and the generation of tidal eddies of length scales larger than the nourishment itself. The present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions, based on extensive field observations and numerical flow simulations. Observations of the flow field around the Sand Motor, obtained with a ship-mounted current profiler and a set of fixed current profilers, show that a tidal eddy develops along the northern edge of the mega-nourishment every flood period. The eddy is generated around peak tidal flow and gradually gains size and strength, growing much larger than the cross-shore dimension of the coastline perturbation. Based on a 3 week measurement period, it is shown that the intensity of the eddy modulates with the spring-neap tidal cycle. Depth-averaged tidal currents around coastline perturbations are simulated and compared to the field observations. The occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape. Results show that several different types of behavior exist, characterized by different combinations of the nourishment aspect ratio, the size of the nourishment relative to the tidal excursion length, and the influence of bed friction.

International audience; Suspended particulate matter (SPM) is a key component of coastal food webs and a key variable of nutrient budgets. Understanding its variability across short time scales in estuaries may help ecologists understand seasonal and diurnal migration of estuarine organisms, and answer how their nutritional requirements are fulfilled. It may also inform biogeochemists regarding the factors that influence import and export of nutrients between terrestrial and coastal ecosystems. This study aimed to link the dynamics of fatty acids, stable isotopes (δ13C and δ15N) and C/N ratios of SPM, revealing organic matter quality, to rapidly varying factors (SPM concentration, salinity and presence of daylight) and comparing this variability to the seasonal variation induced by the alternation of dry and wet seasons in the studied region. Our results revealed that these rapidly varying factors had a strong influence on the bacterial and the phytoplanktonic compartments of SPM. They suggest that tidally resuspended particles are the site of intense heterotrophic activity and that estuarine phytoplankton store lipids during the daytime up to substantially modifying SPM quality. Our study also shows higher freshness of SPM during the wet season. We expect this study to raise the interest of both biologists and biogeochemists to introduce daily variability of SPM in food webs and nutrient budgets modelling.

Electromagnetic induction (EMI) techniques are becoming increasingly popular for near-surface coastal geophysical applications. However, few studies have explored the capabilities and limitations of portable multifrequency EMI profilers for mapping large-scale ([Formula: see text]) barrier island hydrogeology. The purpose of this study is to investigate the influence of groundwater dynamics on apparent conductivity [Formula: see text] to separate the effects of hydrology and geology from the [Formula: see text] signal. Shore-normal and alongshore surveys were performed within a highly conductive barrier island/wind-tidal flat system at Padre Island National Seashore, Texas, USA. Assessments of instrument calibration and signal drift suggest that [Formula: see text] measurements are stable, but vary with height and location across the beach. Repeatability tests confirm [Formula: see text] values using different boom orientations collected during the same day are reproducible. Measurements over a 12 h tidal cycle suggest that there is a tide-dependent step response in [Formula: see text], complicating data processing and interpretation. Shore-normal surveys across the barrier/wind-tidal flats show that [Formula: see text] is roughly negatively correlated with topography and these relationships can be used for characterizing different coastal habitats. For all surveys, [Formula: see text] increases with decreasing frequency. Alongshore surveys performed during different seasons and beach states reveal a high degree of variability in [Formula: see text]. Here, it is argued that surveys collected during dry conditions characterize the underlying framework geology, whereas these features are somewhat masked during wet conditions. Differences in EMI signals should be viewed in a relative sense rather than as absolute magnitudes. Small-scale heterogeneities are related to changing hydrology, whereas low-frequency signals at the broadest scales reveal variations in framework geology. Multiple surveys should be done at different times of the year and tidal states before geologic interpretations can confidently be made from EMI surveys in coastal environments. This strategy enables the geophysicist to separate the effects of hydrology and geology from the [Formula: see text] signal.

Water current, salinity, and suspended sediment concentration (SSC) were measured at three anchored boat sites along the North Passage (NP) of the Changjiang Estuary over a spring-neap tidal cycle, in order to study sediment trapping and siltation in the estuary. Pronounced stratification was observed during the late flood tide and the following early ebb tide, along with an advancing and retreating salt wedge, whereas strong vertical mixing occurred during the late ebb when the effect of the salt wedge faded. Therefore, the SSC in the flood-ebb tidal cycle tended to be asymmetric. In the upper reach of the NP, the seaward advective near-bed sediment transport dominated the total near-bed sediment transport, whereas in the middle reach of the NP, the landward tidal pumping component dominated. Accordingly, a notable convergent near-bed residual sediment transport was generated near the middle reach. Because the convergence of residual sediment transport in the region of a salt wedge is generally recognized as sediment trapping, convergent near-bed residual sediment transport is the cause of the high sedimentation rate in the NP.

At mid-latitudes, sea water temperature shows a strong seasonal cycle forced by the incident surface heat flux. As depth decreases, the heat flux incidence is damped by the horizontal flux, which prevents the indefinite growth of the seasonal temperature range. In the present work, cross-shore transport in the west coast of Nuevo Gulf (Argentina) was analyzed. Processes tending to cool the coastal waters in summer and to warm the coastal waters in winter, were identified through temperature measurements, surface heat flux and tidal height. The simplified models proposed here provide a feedback mechanism that links changes in surface heat flux with changes in the horizontal heat flux during both seasons. On shorter time scales, tide produces significant variations in the height of the water column, therefore influencing temperature fluctuations and the direction of the horizontal flow. Fil: Rivas, Andres Lujan. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Pisoni, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Dellatorre, Fernando Gaspar. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Tecnológica Nacional; Argentina

The Yellow River Estuary (YRE), which is famous for its abundant sediment, rapid accretion, and frequent migration, has experienced a remarkable decrease of sediment transported by the Yellow River (YR) during the past 60 years. By taking the west coast (Yellow River Delta, YRD) and the south coast of Laizhou Bay (LZB) as a unified coastal unit, this paper has analyzed the evolution of shorelines, isobaths, and geomorphic erosion/accretion during the last 60 years based on the remote sensing images and nautical charts; these data were also used to reveal the depositional dynamic mechanisms controlling the coastal geomorphic responses to YRE evolution in a hydrodynamic numerical simulation. Then, the coastal dynamics, subaqueous slope accretion, and geomorphic evolution were integrated spatially. Finally, the impacts of YRE evolution, including changes of the position and amount of sediment loading into the sea, on the coastal geomorphic evolution of western–southern LZB during the recent 60 year period were elucidated. Results showed that outside of the YRE delta lobes, there has always been an arc high-velocity zone, outside of which there has existed a northeast arc tidal shear frontal zone during the last 60 years. As the estuary delta lobes extended into the sea, the high-velocity zone moved toward the southeast, where its range and velocity also increased. As an overall trend, the duration of the tidal shear frontal zone (TSFZ) has grown longer and longer over a whole tidal cycle, while the interval time has grown shorter and shorter; moreover, the span between the southern and northern endpoints has grown larger and larger, while the southern end always remained confined to a fixed position in the northeast sea area of Qingtuozi. Under the control of TSFZ, the suspended sediment of the Yellow River deposits nearly entirely in the arc area in the vicinity of the estuary delta lobes on the west coast, and thus, the sediment cannot cross TSFZ and move into southern LZB. As a result, the western and southern coasts of LZB have shown significant differences in the evolution of shorelines, isobaths, and geomorphic erosion/accretion during the last 60 years. That is, these features have changed dramatically in the west coast but have remained relatively stable in the southern coast, and sediment deposition is now greatly reduced in the southern LZB. Therefore, the YRE evolution had a significant geomorphic impact on the coast of western LZB where the YRD is located, while it had only a slight impact on southern LZB.

Seabed erosion is a vital process for sediment transport in estuaries and coasts. In this study, we investigated the seabed erosion process and its spatiotemporal variability in the Pearl River Estuary, China, via in-situ observations and laboratory experiments. It is found that the seabed was more erodible in the channel than at the shoal in most cases due to the difference in sediment size. In a neap-spring-neap tidal cycle, a laminated seabed with different sediment ages was inferred to form due to deposition on flood tides and erosion on ebb tides. The seabed was more erodible during spring tides than neap tides because of the difference in sediment availability at the unconsolidated fresh layer. Furthermore, the erosion curve showed evident flood-ebb asymmetry, which was found to be related to the variations of sediment availability and bottom stress. Besides, erosion experiments with different sediment consolidations revealed that sediment erodibility decreased with the growth of consolidation. This study promotes our understanding on the spatiotemporal variability of sediment erodibility, and has significant implications for simulation and prediction of estuarine sediment transport and morphological evolution.

Tidal fronts are interfaces that separate stratified from mixed waters. The stratified surface zone of a front has lower inorganic nutrient concentrations than the mixed side, and thus, phytoplankton assemblages are expected to differ from one side of the front to the other. Here, we characterize the physics, nutrient dynamics, and biology of the southern front in San Jorge Gulf (SJG), Argentina, during a spring-neap tidal cycle. Baroclinic instabilities influence the shape and position of the front and presumably play an important role in the horizontal transport across the front. The highest phytoplankton biomass concentrations were found in the waters of the stratified side of the front during neap tide, with picophytoplankton, cyanobacteria, and nanophyto-plankton being the main contributors to the total autotrophic biomass. Bacteria contribute the most to heterotrophic biomass. In contrast, during spring tide, the carbon contribution of microphytoplankton was higher than during neap tide. In the mixed side, cells photoacclimate to optimum light conditions, suggesting that cells near the surface, which are probably photoinhibited, and cells below the euphotic zone, which are light-limited, are quickly advected by turbulent vertical motions to depths with optimal irradiance conditions., Facultad de Ciencias Naturales y Museo

San Jorge Gulf (SJG) is a region of high biological productivity that supports important shrimp (Pleoticus muelleri) and hake (Merluccius hubbsi) fisheries, as well as high marine biodiversity associated, in part, with a tidal front located in the southern part of the gulf. In situ high-resolution cross-frontal measurements were collected using a remotely operated towed vehicle to characterize the three-dimensional structure of the tidal front and to investigate how its position varies during the semidiurnal tidal cycle (high/low) and the spring to neap transition, together with its impact on the distribution of nutrients and chlorophyll-a. Estimates of tidal height and flow velocity derived from a numerical model support the conclusion that frontal displacements mostly result from advec-tion by cross-frontal tidal currents. The frontal position was also modified by baroclinic instabilities that significantly distort the front. Measurements reveal intrusions of low-salinity, nutrient-rich waters from the mixed side into the pycnocline on the stratified side cause a subsurface chlorophyll-a peak near the neap phase. Most prior studies of fronts in the SJG have been limited to their surface manifestations because they were conducted using satellite images. This article aims to contribute to the understanding of the complex southern tidal front dynamics, highlighting that maximum primary productivity occurs in a subsurface layer that is not visible by satellite sensors. Fil: Carbajal, Juan Cruz. Centro Para El Estudio de Sistemas Marinos (cesimar), Conicet-cenpat; Argentina Fil: Rivas, Andres Lujan. Centro Para El Estudio de Sistemas Marinos (cesimar), Conicet-cenpat; Argentina Fil: Chavanne, Cédric. Institut Des Sciences de la Mer de Rimouski; Canadá

It will not be practical for tidal stream turbines to extract all the peaks in energy over the tidal cycle. It is widely assumed that some form of power capping strategy will be required. In this paper we examine this using a 2D shallow water model of tidal hydrodynamics of the Pentland Firth. We argue that in addition to power capping, it is sensible to control the turbines to limit the peak thrust on them. We show that this can lead to a significant reduction in the peak thrust applied to the turbines and smaller changes to the naturally occurring flow rate whilst having a minimal effect of the mean power generated.

Earth embankments are utilized as protective structures along river, coastal banks and maybe thus exposed to steady or transient seepage induced by tides. In the Indian part of Sunderban region, the tidal head variation is 4–6 m in cycle time of 12 h. A model has been developed in FEM-based software, GeoStudio, to study the effect of transient seepage in such an embankment. The response to tidal head was found to be limited to a certain zone within the embankment. The cyclic pore water pressure distribution was seen to differ in various regions in this zone. Also, even though the cyclic FOS against stability was adequate, serviceability check indicates chances of failure near toe region.

The Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. In this paper, we report on shorter period solitary-like waves that are consistent with a mode-2 vertical structure, which are observed along the Ten Degree Channel, and propagate side-by-side the usual large mode-1 solitary wave packets. The mode-2 waves are identified in TerraSAR-X images because of their distinct surface signatures, which are reversed when compared to those that are typical of mode-1 ISWs in the ocean. These newly observed regularly-spaced packets of ISW-like waves are characterized by average separations of roughly 30 km, which are far from the nominal mode-1 or even the mode-2 internal tidal wavelengths. On some occasions, five consecutive and regularly spaced mode-2 ISW-like wave envelopes were observed simultaneously in the same TerraSAR-X image. This fact points to a tidal generation mechanism somewhere in the west shallow ridges, south of the Nicobar Islands. Furthermore, it implies that unusually long-lived mode-2 waves can be found throughout the majority of the fortnightly tidal cycle. Ray tracing techniques are used to identify internal tidal beams as a possible explanation for the generation of the mode-2 solitary-like waves when the internal tidal beam interacts with the ocean pycnocline. Linear theory suggests that resonant coupling with long internal waves of higher-mode could explain the longevity of the mode-2 waves, which propagate for more than 100 km. Owing to their small-scale dimensions, the mode-2 waves may have been overlooked in previous remote sensing images. The enhanced radiometric resolution of the TerraSAR-X, alongside its wide coverage and detailed spatial resolutions, make it an ideal observational tool for the present study.

The increased availability of civil SAR (Synthetic Aperture Radar) satellite images with different resolution allows us to compare the imaging capabilities of these instruments, to assess the quality of the available data, and to investigate different areas (e.g., the Wadden Sea region). In our investigation, we propose to explore the content of TerraSAR-X and Sentinel-1A satellite images via a data mining approach in which the main steps are patch tiling, feature extraction, classification, semantic annotation, and visual-statistical analytics. Once all the extracted categories are mapped and quantified, then the next step is to interpret them from an environmental point of view. The objective of our study is the application of semi-automated SAR image interpretation. Its novelty is the automated multi-class categorisation of coastal areas. We found out that the north-west of the Netherlands can be interpreted routinely as land surfaces by our satellite image analyses, while for the Wadden Sea we can discriminate the different water levels and their impact on the visibility of the tidal flats. This necessitates a selection of time series data spanning a full tidal cycle.

The classification of a lagoon as a restricted lagoon is shown to depend not solely on its geometry but also on the tidal hydraulics. By numerically simulating the tidal exchange of two lagoons of similar geometrical dimensions, the Nidova lagoon and the Papas lagoon, in Western Greece, subject to very similar tidal forcing, applied to the two tidal inlets in the first case and three in the second, very different residence times are found, namely 2.5 days for the Nidova and 25–30 days for the Papas lagoon. This large difference is attributed to the fact that whereas the Papas lagoon functions as a typical restricted lagoon, in which the water renewal is achieved by mixing in the lagoon of the tidal prism water exchanged within a tidal cycle, the Nidova lagoon functions as a flow-through system because of the differential arrival of the tide at its two tidal inlets. It is suggested that this way of enhancing the flushing rate of a lagoon be considered, whenever possible, when creating a new tidal inlet to the lagoon.

The article of record as published may be found at http://dx.doi.org/10.1029/2018JC013987 Ocean‐driven melting of ice shelves is a primary mechanism for ice loss from Antarctica. However, due to the difficulty in accessing the sub‐ice shelf ocean cavity, the relationship between ice shelf melting and ocean conditions is poorly understood, particularly near the grounding zone, where the ice transitions from grounded to floating. We present the first borehole oceanographic observations from the grounding zone of the Ross Ice Shelf, Antarctica's largest ice shelf by area. Contrary to predictions that tidal currents near grounding zones mix the water column, we found that Ross Ice Shelf waters were vertically stratified. Current velocities at middepth in the ocean cavity did not change significantly over measurement periods at two different parts of the tidal cycle. The observed stratification resulted in low melt rates near this portion of the grounding zone, inferred from phase‐sensitive radar observations. These melt rates were generally

We search for possible localized tidal triggering in earthquake occurrence near Japan by testing for tidal periodicities in seismicity within a variety of space/time bins. We examine 74,610 earthquakes of M ≥3 in the Japan Meteorological Agency (JMA) catalog from January 2000 to April 2013. Because we use many earthquakes for which accurate focal mechanisms are not available, we do not compute tidal stresses on individual fault planes, but instead assume that the mechanisms are likely to be similar enough among nearby events that tidal triggering will promote earthquake occurrence at specific tidal phases. After dividing the data into cells at a range of spatial (0.2∘, 0.5∘, 1.0∘) and temporal dimensions (100, 200, 400 days), we apply Schuster's test for non-random event occurrence with respect to both the semi-diurnal and semi-monthly tidal phases. Because the resulting p-values will be biased by temporal clustering caused by aftershocks, we apply a declustering method that retains only one event per tidal cycle per phase increment. Our results show a wide range of p-values for the localized earthquake bins, but the number of bins with very small p-values (e.g., p < 0.05) is no more than might be expected due to random chance, and there is no correlation of low p-value bins with the time of the 2010 M 9.0 Tohoku-oki earthquake.

Salt intrusion has some negative impact on the estuarine eco-environment as well as the water resource potential. The paper proposes an analytical model to describe salt intrusion in the estuaries with multiple freshwater sources. The impact of river discharge on the salinity distribution changes along the multiple-fresh-source estuaries, which is different from estuaries with single source of freshwater. Our analytical model is derived from the advection–dispersion equation for salinity while taking into account the hydrodynamic variation along the estuary. In this paper, we take the Humen Estuary, a strongly tide-dominated estuary with two major source of freshwater, as an example to illustrate the model. By testing against eight surveys over a complete spring-neap tidal cycle, the analytical model’s capacity to describe salt intrusion in the Humen Estuary is calibrated and validated. The results show that the analytical method can be used to compute the salinity distribution in the multiple-freshwater-source estuaries. In comparison with the field data in the Humen Estuary, the calculated results indicate that the salt intrusion process exhibits remarkable segmentation in the multiple-freshwater-source estuary, although the estuary’s inherent characteristic remains the same throughout the estuary. Moreover, by analyzing the multi-segmental features of the Humen Estuary, an efficient and effective model to predict the salt intrusion length of the Humen Estuary is presented and satisfactory results are obtained to illustrate its practical application.

To study cohesive sediment behaviors and their time-variability in the near-bottom layer in the muddy area of the northern Taiwan Strait (TS), a short-term bottom-mounted tripod, which was equipped with an acoustic Doppler velocimeter (ADV), an upward acoustic Doppler current profiler (ADCP) and a CTD with a Seapoint turbidity sensor, was deployed at the northern TS over seven days between July 22 and 29, 2012. The near-bed current velocity, wave orbital velocity, bottom shear stress induced by wave and current, near-bed suspended sediment concentration (SSC) and variations in the bed elevation were resolved. The observation results indicate that the most important semidiurnal constituent at the northwest TS is M2 and that the near-bed (0.7 mab) current speed showed spring-neap cyclic characteristics, with a maximum value of 0.453 m/s. Additionally, the water flowed in acounter-clockwise rotary current pattern. The weather was fair during the observation, and the significant wave height ranged from 0.60 m to 1.81 m, which generated an extremely low wave orbital velocity (the maximum value was 0.128 m/s). The near-bed SSC estimated from the signal-noise ratio recorded by the ADV ranged from 1.48 mg/L to 74.95 mg/L. The relation between the bottom shear stress and the SSC suggested that the local sediment resuspension is primarily controlled by a tidal current and that the wave action was practically negligible during the observation. The resulting net near-bed horizontal transport flux was 1387.59 kg/m2 during the observations, dominated by the along-shelf flux (approximately 3.74 times than cross-shelf flux) and directed toward the NNE. The bed elevation revealed that the mean value of the erosion and deposition depth during a tidal cycle could reach 14.8 mm in an intermediate tide, with a maximum value of 17.9 mm; the net effect during the observation was erosion, with a depth of 0.4 mm.

Oil from the 1989 Exxon Valdez oil spill persists in many gravel beaches in Prince William Sound (Alaska, USA), despite great remedial efforts. A tracer study using lithium at a gravel beach on Knight Island, Prince William Sound, during the summer of 2008 is reported. The tracer injection and transport along a transect were simulated using the two-dimensional numerical model MARUN. Model results successfully reproduced the tracer concentrations observed at wells along the transect. A sensitivity analysis revealed that the estimated parameters are well determined. The simulated spatial distribution of tracer indicated that nutrients applied along the transect for bioremediation purposes would be washed to the sea very quickly (within a semi-diurnal tidal cycle) by virtue of the combination of the two-layered beach structure, the tidal fluctuation and the freshwater flow from inland. Thus, pore-water samples in the transect were found to be clean due to factors other than bioremediation. This may explain why the oil did not persist within the transect.

A field study was conducted on a dissipative beach to quantify inner surf and swash-zone bed level change during periods of inundation and throughout a tidal cycle. Elevation changes were acquired at millimeter resolution with a new conductivity concentration profiler that allowed quantification of the bed level throughout the duration of the wave/swash cycle and also during periods of bed exposure. Bed level change spectra showed the highest energy at low frequencies even though event-scale net bed level changes were observed to exceed the tidal-scale net bed level change. Net bed level change for individual events was nearly normally distributed with most individual events displaying little or no net bed level change. “Large” erosion and accretion events with bed level elevation magnitudes that exceeded net tidal elevation change occurred with similar frequency. The similarity between the frequency of large erosion and large accretion events suggests that a few events may be ultimately responsible for the observed net elevation change over the tidal cycle. The large events displayed different hydrodynamic characteristics. Erosion events had longer duration onshore-directed flow and higher maximum onshore-directed velocity magnitude than offshore-directed velocity magnitude. The opposite was found for accretion events that had longer duration offshore-directed flow and a higher maximum offshore-directed velocity magnitude than onshore-directed velocity magnitude.

[1] We combine the dynamics of ice, bed, and ocean in a new elastic model for the tidal-timescale migration of grounding lines on deformable foundations. Previous interpretations of tidal flexure using models of elastic ice shelves with fixed grounding lines were found to be inconsistent, suggesting an elasticity of ice that varies spatially and temporally and that is significantly smaller than measured experimentally. We argue here that with our model, a consistent, purely elastic interpretation can be made. Combining this new approach with remote-sensing measurements, we show that the grounding line migrates several kilometers during a tidal cycle, that we can infer the effective elastic properties of the bed, and that the elastic pressure of the ice leads to a hydrological barrier near the grounding line that controls subglacial hydrology. Our findings imply that subglacial lubrication and melting induced by the ocean thermal forcing can increase substantially during high tide.

This work shows statistical evidence for lunar nodal cycle influence on the low-frequency summer rainfall variability over the plains to the east of subtropical Andes, in South America, through long-term sea surface temperature (SST) variations induced by the nodal amplitude of diurnal tides over southwestern South Atlantic (SWSA). In years of strong (weak) diurnal tides, tide-induced diapycnal mixing makes SST cooler (warmer) together with low (high) air pressures in the surroundings of the Malvinas/Falklands Islands in the SWSA, possibly through mean tropospheric baroclinicity variations. As the low-level tropospheric circulation anomalies directly affect the interannual summer rainfall variability, such an influence can be extended to the bi-decadal variability present in the summer rainfall owing to the nodal modulation effect observed in the tropospheric circulation. The identification of the nodal periodicity in the summer rainfall variability is statistically robust.

Experimental data obtained in the summer of 2011 in three White Sea continental shelf areas with different stratification are analyzed. The measurements were conducted using a unified procedure that combines frequent oceanographic stations (scanning) and deployment of moorings. It is shown that the tide-induced variability of the thermohaline fields and internal waves is of different types. A shelf area is detected where intense short-period internal waves are observed during every tidal cycle and their contribution to water mixing is significant.

In this study, field measurements were conducted in the section about 7 km from sea dike to westward. The observations of along channel current were carried out, and water temperature and salinity were measured simultaneously at 10 stations during one tidal cycle, and sampling interval is 1 hour. The maximum ebb current is about 1.5 m/s at the surface layer but flood current is 0.4 m/s at the bottom layer during discharge period. Residual current during river discharge shows two layer structures which is typical characteristic of the estuary system. On the other hand, residual current during a period with no discharge has shown multi-layer structure different from general estuarine systems. The distribution of high salinity can be seen at the bottom layer as the effect of discharge does not reach down to the bottom layer during discharge. As a result, freshwater is not effected at the bottom layer during observation, and mixing of surface layer to bottom layer is reduced by stratification.

International audience; Tide gauge and meteorological data were used to analyze tidal fluctuations and relative sea level (RSL) variability in the microtidal fringing reef of La Saline, at La Reunion, Western Indian Ocean, for 58 days during late summer 2005. Harmonic analysis was applied to evidence tidal constituents and to predict tidal variations in the open ocean and in the fringing reef. The predicted signals were compared to assess the intratidal and supratidal variability as well as the synoptic response of the RSL in the reef. Finally, the non-tidal fluctuations of the signal recorded in the fringing reef were correlated with the external forcing data (wind and wave). The results show that the tide in the reef is reduced and delayed, compared to the tide of the open ocean. The neap-spring tidal cycle in the fringing reef appears more synchronized on the tropical cycle (27.32 days) of the Moon, rather than its synodic cycle (29.52 days). Due to the shallowness of the fringing reef, nonlinear bottom-friction interactions induce an amplification of compound tides, the fortnightly (Msf) and monthly (Mm) long-period tides (LPT), which have a major influence on the relative sea surface elevations variations. They cause relative high and low RSL reaching ±10 cm in the fringing reef, which are significantly different from the sea level in the open ocean. It appears that the contribution of the external forcing to the RSL fluctuations in the fringing reef will largely depend on these high and low sea levels. Our results demonstrate that the orbital moon cycles and the LPT cannot be neglected in upcoming studies of narrow microtidal fringing reefs, involving sea level variations.

This study identifies and unravels the processes that lead to stratification and destratification in the far field of a Region of Freshwater Influence (ROFI). We present measurements that are novel for two reasons: (1) measurements were carried out with two vessels that sailed simultaneously over two cross-shore transects; (2) the measurements were carried out in the far field of the Rhine ROFI, 80 km downstream from the river mouth. This unique four dimensional dataset allows the application of the 3D potential energy anomaly equation for one of the first times on field data. With this equation, the relative importance of the depth mean advection, straining and nonlinear processes over one tidal cycle is assessed. The data shows that the Rhine ROFI extends 80 km downstream and periodic stratification is observed. The analysis not only shows the important role of cross-shore tidal straining but also the significance of along-shore straining and depth mean advection. In addition, the nonlinear terms seem to be small. The presence of all the terms influences the timing of maximum stratification. The analysis also shows that the importance of each term varies in the cross-shore direction. One of the most interesting findings is that the data are not inline with several hypotheses on the functioning of straining and advection in ROFIs. This highlights the dynamic behaviour of the Rhine ROFI, which is valuable for understanding the distribution of fine sediments, contaminants and the protection of coasts.

The IPCC global sea-level rise projections made in 1990 set the framework for the coastal policy response to sea-level rise in England and Wales. It was predicted that sea-level rise would result in an increase in wave energy at the cliff foot and accelerated cliff recession. The 50 year recession records for the Holderness cliffs, UK, have been examined to establish whether there has been acceleration in recession rates since the early 1990s. As relative sea level has risen over the second half of the 20th century, so have Holderness cliff recession rates, from around 1.2 m a −1 in the early 1950s to around 1.5 m a −1 by 2000. However, there has been no significant acceleration in the rate of global sea-level rise since 1990 and no rapid increase in the recession rate. However, the Holderness data series may show responses to decadal-scale sea-level changes associated with the 18.6 year nodal tidal cycle.

Summary An investigation was conducted to characterize the spatial and temporal distribution of the hyporheic zone of a large tidally influenced river. The field site is located on the Fraser River in British Columbia, Canada, approximately 30 km from its outlet to the ocean. The physical attributes of the riverbed were mapped using geophysical techniques coupled with sediment sampling. The spatial and temporal distribution of groundwater composition beneath the riverbed was determined through detailed profiling. Contaminated (fresh) groundwater discharges through a narrow band of the riverbed at a distance approximately 88–105 m from the shoreline coinciding with the termination of a massive silty unit. Saline groundwater, as part of a regional flow system, dominates the riverbed sediments from 105 m beyond the shoreline towards the centre of channel. Three water types occur within the upper 2 m of the riverbed sediments; a result of both mixing of river water, contaminated (fresh) groundwater, and saline groundwater and modification by cation exchange reactions. The interaction of these waters produced distinct zones of Ca– HCO 3 - , Na–Cl, and Ca–Cl type waters. The distribution of groundwater solutes indicates that during a single tidal cycle, river water penetrates the riverbed to a depth of approximately 15 cm but the long term effects of tidal pumping of river water into the riverbed is observed to a depth of approximately 1 m below the river bed.

Interpretation of the evolution of the tidal cycle in Minas Basin and upper Bay of Fundy (Scots Bay) based on molluscan assemblages agrees well with that derived by AMOS (1978) from sedimentological evidence. Prior to about 6300 years B.P. quiet water conditions, i.e. with minimal or no tidal activity, prevailed. From that time, tidal range and intensity have increased to their present levels. The molluscs show this change by a change from intact specimens of deposit feeders at, or near, the base of two of the vibrocores, through a mixture of incomplete specimens and suspension feeders, to accumulations of minute, unidentifiable shell fragments., Une interprétation de l’évolution du cycle des marées dans le bassin des Mines et le fond de la baie de Fundy (baie Scots), fondée sur les assemblages de mollusques, correspond bien à celle qu’AMOS (1978) adonnée en se basant sur des preuves sédimentologiques. Avant environ 6300 BP, les eaux étaient calmes, c’est-à-dire qu’il y avait peu ou pas de marées. Par la suite, l’amplitude et l’intensité des marées se sont accrues pour atteindre les niveaux actuels. L’examen des mollusques de deux des carottes, obtenues par vibration, confirme cette interprétation puisque l’on passe de spécimens intacts de mangeurs de sédiments, à la partie inférieure des forages, à un mélange de spécimens incomplets de mangeurs de sédiments et de mangeurs de matières en suspension, puis à des accumulations de fragments d’écaillés minuscules et non identifiables, vers le sommet.

Studies on the water and suspended matter concentration dynamics were performed for the summer and autumn periods in Kruglaya Bay, Chupa Inlet (Karelian Coast, the White Sea). The tidal cycle appeared as the major factor defining the water salinity, temperature, and suspended matter concentration. The water temperature and suspended matter concentration increased during low tide, and the opposite pattern was observed for water salinity; all the processes were true for both surface and bottom water layers. Therefore, we conclude that major bulk of the allochtonous suspended matter is carried into the sea by the ebb stream.

During 2006–2007, the KwaZulu-Natal coast of South Africa was exposed to several large swell events (Ho > 3 m), near the peak of the lunar nodal cycle, causing shoreline recession. The largest swell (Hs = 8.5 m) struck the coast on the March equinox (18th–20th) and generated a strong storm-return flow. Observations made before, during and after record dramatic coastal erosion (shoreline recession of up to 40 m and substantial property damage). This swell event removed the semi-continuous nearshore bar system and ‘conditioned’ the coast such that lesser subsequent swell events accomplished much greater amounts of coastal erosion than expected (up to 100 m at certain erosion hotspots) because waves reached the coast without significant energy dissipation. Subsequent bar generation rebuilt the inshore bars within six months. The styles of erosion during the March ’07 event and other 2007 swells were markedly different. Lesser swells are focused by headlands and result in megarip development and activation of erosion hotspots. The March ’07 event still-water level was raised (equinoctial spring high tide and a storm surge of 0.33–0.45 m) to a level that rendered most headlands (and erosion hotspots) ineffective and resulted in laterally extensive erosion of soft shorelines. Results record cumulative effects of successive swell events on coastal behaviour that proved to be critical in enabling erosion to proceed at rapid rates after the coast had been initially destabilized. Unlike hurricanes and tsunamis, surges associated with swell events are relatively minor and therefore extensive erosion is linked with high lunar tides. There is circumstantial evidence that swell-induced erosion follows the broad 18.6 yr lunar nodal tidal cycle when the chances of large swells coinciding with high water levels are increased.

Laboratory and field work was conducted to determine rates of surface downwearing on shore platforms at two sites in the Bay of Fundy, Canada; these data are needed to assess and model the effect of downwearing mechanisms on platform evolution. Sandstone and basalt samples (900) were exposed to semidiurnal tidal cycles over 3 years, using de-ionized water or artificial sea water. They were immersed for 1, 6, or 11 h over each 12 h tidal cycle, representing the lowest high (LHT), mid-, and highest low (HLT) tidal levels, respectively. A further 600 samples were immersed in de-ionized water or artificial sea water for 90 min every 1, 2, or 3 weeks, representing increasingly higher elevations above the LHT level, or exposed for 90 min every 1, 2, or 3 weeks, representing increasingly lower elevations below the HLT level; these experiments ran for 12 months. In the field, surface downwearing was measured at 108 transverse micro-erosion meter (TMEM) stations over 2 to 6 year periods. In the laboratory, mean downwearing rates between the LHT and HLT levels were 0.61–1.80 mm yr − 1 in sandstones and 0.01–0.18 mm yr − 1 in basalts; rates were highest at the LHT level. Rates decreased with elevation above the LHT level and were uniformly low below the HLT level. Salt weathering was dominant above the LHT level. Salt weathering and wetting and drying were important in sandstones between the LHT and HLT levels, but salts inhibited rock breakdown in basalts. In the field, the mean downwearing rate was 1.254 mm yr − 1 in sandstones, which was similar to the experimental data, and 0.722 mm yr − 1 in basalts, which was much higher than in the experiments with artificial sea water but similar to the experiments with de-ionized water. There was no relationship in the field between downwearing rate and rock hardness or TMEM station elevation.

Rivers and estuaries can be highly energetic and present a challenging environment for sonar deployment and observation. To better understand this environment, a high-frequency, wide-sector forward-looking bathymetric sonar was used to observe tidal phenomena in the lower Connecticut River in June 2017. The stationary sonar system provided Eulerian measurements of the lower estuary for a complete tidal cycle, covering a large portion of the main channel. The system was able to map the observed region and differentiate between bathymetry and non-stationary phenomena in the water column. The data highlight the difference in acoustic propagation for the different phases of the tidal cycle. Doppler processing of the data shows the motion of various subsurface features in the river. These data are compared with other observations, including simultaneous in situ point measurements of salinity, temperature and turbidity from a REMUS 100 AUV. The data from this experiment can be used to improve the understanding of acoustic propagation in riverine and estuarine environments. [Work sponsored by the Office of Naval Research.]Rivers and estuaries can be highly energetic and present a challenging environment for sonar deployment and observation. To better understand this environment, a high-frequency, wide-sector forward-looking bathymetric sonar was used to observe tidal phenomena in the lower Connecticut River in June 2017. The stationary sonar system provided Eulerian measurements of the lower estuary for a complete tidal cycle, covering a large portion of the main channel. The system was able to map the observed region and differentiate between bathymetry and non-stationary phenomena in the water column. The data highlight the difference in acoustic propagation for the different phases of the tidal cycle. Doppler processing of the data shows the motion of various subsurface features in the river. These data are compared with other observations, including simultaneous in situ point measurements of salinity, temperature and turbidity from a REMUS 100 AUV. The data from this experiment can be used to improve the understanding ...

A field experiment was conducted on a high energy sandy beach (Truc Vert, France) to examine swash zone processes and shoreline erosion–accretion in response to changing wave and tide conditions. Beachface morphological changes were measured at the swash-by-swash timescale using an array of ultrasonic bed-level sensors and at the tidal timescale through total station surveys. Hydrodynamic and sediment dynamic data were collected using arrays of pressure transducers, electromagnetic current meters, optical backscatter sensors and total load sediment traps. Data were collected for 16 consecutive days (33 tides) over a spring–neap–spring tidal cycle with offshore significant wave heights of 1–4 m and periods of 5–12 s. The swash motion was predominantly at infragravity wave frequencies. Over the measurement period, the upper beach experienced phases of accretion, erosion and stability. Trapped sediment loads for the uprush and backwash were predicted reasonably well by cross-shore velocity skewness, but the prediction of net transport over individual swash events by velocity-based models was more problematic, particularly lower in the swash zone where swash interactions were more prevalent. Net sediment fluxes over individual swash events often exceeded 100 kg per unit meter beach width and such rates were only one order of magnitude less than the net transport typically experienced across the high tide swash zone over complete tidal cycles. Upper beach erosion–accretion at the tidal timescale was reasonably well predicted by the Dean criterion based on offshore wave steepness and dimensionless fall velocity, but the beach gradient also played a significant role in controlling the occurrence of erosion and accretion.

Ensemble-averaged suspended sediment concentrations (SSC) and transport from the swash zone of a high-energy beach are investigated with respect to the time-averaged setup level obtained from calibrated video records. Ensemble-averaged data indicate variability in SSC between both uprush and backwash during rising and falling tides. Mean ebb-tide SSC exceeds mean flood-tide SSC during both the uprush (by 28–34%) and backwash (by up to 25%). Suspended sediment concentration also varies between swash phases over a tidal cycle with mean uprush SSC exceeding mean backwash SSC by 46% to 108% depending on tidal level, with a general percentage decrease during the falling tide. The net ensemble-averaged transport (velocity-SSC product) magnitude displays a decreasing trend from roughly 30 to 20 kg m−1 during the rising tide and from roughly 45 to 15 kg m−1 during the falling tide that cannot be explained based on the percentage of foreshore immersion (water depth) alone. Thus, relative tidal level (cros...

Repeated high-resolution multibeam bathymetric surveys from 2002 through 2006 at the head of the Monterey Submarine Canyon reveal a sandwave field along the canyon axis between 20 and 250 m water depth. These sandwaves range in wavelength from 20 to 70 m and 1 to 3 m in height. A quantitative measure was devised to determine the direction of sandwave migration based on the asymmetry of their profiles. Despite appreciable spatial variation the sandwaves were found to migrate in a predominantly down-canyon direction, regardless of season and tidal phases. A yearlong ADCP measurement at 250 m water depth showed that intermittent internal tidal oscillations dominated the high-speed canyon currents (50–80 cm/s), which are not correlated with the spring–neap tidal cycle. Observed currents of 50 cm/s or higher were predominantly down-canyon. Applying a simple empirical model, flows of such magnitudes were shown to be able to generate sandwaves of a size similar to the observed ones.

A methodology for monitoring long-term beach face volume change with a combination of intermittent profiling and video imagery is developed. Intertidal beach morphology can be mapped from video with the use of movement of the waterline over a tidal cycle. Such maps provide detailed information on spatial and temporal evolution of the intertidal area, but no direct information on beach face volume changes as a whole. However, beach face volume might well be correlated with cross-shore changes to a contour located in the intertidal zone. This is significant because such a parameter can be calculated from maps of the intertidal morphology generated with video images. This idea was tested with a series of video images and surveys that were collected over a year and a half on an intermediate beach on the Coromandel Peninsula, New Zealand, over a wide range of conditions. The surveyed profiles show a strong (r2 = 0.95) relationship between the surveyed cross-shore location of the 2-m contour and the su...

Summary. A reduced equation of motion is used to compute the residual velocity and the residual transport through the West Solent from the water levels recorded over an eight-month period at tide gauges at either end of the channel. A coefficient of bottom friction of 5·0 × 10−3 is assumed. There was a spring-neap variation and a significant correlation of fluctuations in the residual velocity with meteorological conditions. Westward residual velocities occurred at spring tides with low barometric pressure and south-westerly winds. Eastward residual velocities occurred at neap tides with high pressure and north-easterly winds. Because of the progressive nature of the tidal wave the long term residual transport appeared to be towards the west and the flushing time for the Solent system was long for considerable periods. The maximum velocities experienced during a tidal cycle half way along the channel are towards the west with a probability of values exceeding 160 cm s−1 for 10 min in 5·4 days.