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Surface current velocity from high-frequency radar data are used to study tidal currents in the Mid-Atlantic Bight, which represent an average 32% of the total kinetic energy of the surface circulation. Average annual and seasonal tidal current characteristics and the associated variance of the semi-major axis are computed. The M2 constituent dominates the tide, representing a maximum of 72.26% and an average of 51.63% of the total studied tidal signal. Its semi-major axis reaches a maximum of 10 cm s−1 around mid-shelf and its phase sweeps from north to south. Local maxima of the same order of magnitude are found near the mouths of estuaries (Long Island Sound, Hudson River, Delaware Bay, Chesapeake Bay) and an absolute maximum of 50 cm s−1 is found in Nantucket Shoals. These regions of localized elevated tidal amplitude are associated with high interannual and intra-annual variability due to seasonal stratification, internal waves, and sand waves. Seasonal tidal changes are large in some of these regions; thus, should not be neglected in making tidal predictions. Lastly, the authors position this paper as an updated alternative to the Moody tidal atlas as the source for tidal current values in the Mid-Atlantic Bight.

The Arctic Ocean is a challenging region for tidal modelling. The accuracy of the global tidal models decreases by several centimeters in the Polar Regions, which has a large impact on the quality of the satellite altimeter sea surface heights and the altimetry-derived products. NOVELTIS, DTU Space and LEGOS have developed Arctide2017, a regional, high-resolution tidal atlas in the Arctic Ocean, in the framework of an extension of the CryoSat Plus for Ocean (CP4O) ESA STSE (Support to Science Element) project. In particular, this atlas benefits from the assimilation of the most complete satellite altimetry dataset ever used in this region, including Envisat data up to 82°N and CryoSat-2 data between 82°N and 88°N. The combination of these satellite altimetry missions gives the best possible coverage of altimetry-derived tidal constituents. The available tide gauge data were also used for data assimilation and validation. This paper presents the implementation methodology and the performance of this new regional tidal model in the Arctic Ocean, compared to the existing global and regional tidal models.

Previous tidal energy studies in Puget Sound have focused on major deep channels such as Admiralty Inlet that have a larger power potential. This paper focuses on the possibility of extracting tidal energy from minor tidal channels of Puget Sound by using a hydrodynamic model to quantify the power potential and the associated impact on tidal circulation. The study site is a multi-inlet bay system connected by two narrow inlets, Agate Pass and Rich Passage, to the Main Basin of Puget Sound. A three-dimensional hydrodynamic model was applied to the study site and validated for tidal elevations and currents. We examined three energy extraction scenarios in which turbines were deployed in each of the two passages and concurrently in both. Extracted power rates and associated changes in tidal elevation, current, tidal flux, and residence time were examined. Maximum instantaneous power rates reached 250 kW, 1550 kW, and 1800 kW, respectively, for the three energy extraction scenarios. Model results suggest that with the level of energy extraction in the three energy extraction scenarios, the impact on tidal circulation is very small. It is worth investigating the feasibility of harnessing tidal energy from minor tidal channels of Puget Sound.

The tidal stream energy sector is now at the stage of deploying the world's first pre-commercial arrays of multiple turbines. It is time to study the environmental effects of much larger full-size arrays, to scale and site them appropriately. A theoretical array of tidal stream turbines was designed for the Pentland Firth (UK), a strait between Scotland and the Orkney Islands, which has very fast tidal currents. The practical power resource of a large array spanning the Pentland Firth was estimated to be 1.64 GW on average. The ocean response to this amount of energy extraction was simulated by an unstructured grid three-dimensional FVCOM (Finite Volume Community Ocean Model) and analysed on both short-term and seasonal timescales. Tidal elevation mainly increases upstream of the tidal array, while a decrease is observed downstream, along the UK east coast. Tidal and residual flows are also affected: they can slow down due to the turbines action or speed up due to flow diversion and blockage processes, on both a local and regional scale. The strongest signal in tidal velocities is an overall reduction, which can in turn decrease the energy of tidal mixing and perturb the seasonal stratification on the NW European Shelf.

The Taiwan Strait has recently been proposed as a promising site for dynamic tidal power systems because of its shallow depth and strong tides. Dynamic tidal power is a new concept for extracting tidal potential energy in which a coast-perpendicular dike is used to create water head and generate electricity via turbines inserted in the dike. Before starting such a project, the potential power output and hydrodynamic impacts of the dike must be assessed. In this study, a two-dimensional numerical model based on the Delft3D-FLOW module is established to simulate tides in China. A dike module is developed to account for turbine processes and estimate power output by integrating a special algorithm into the model. The domain decomposition technique is used to divide the computational zone into two subdomains with grid refinement near the dike. The hydrodynamic processes predicted by the model, both with and without the proposed construction, are examined in detail, including tidal currents and tidal energy flux. The predicted time-averaged power yields with various opening ratios are presented. The results show that time-averaged power yield peaks at an 8% opening ratio. For semidiurnal tides, the flow velocity increases in front of the head of the dike and decreases on either side. For diurnal tides, these changes are complicated by the oblique incidence of tidal currents with respect to the dike as well as by bathymetric features. The dike itself blocks the propagation of tidal energy flux.

This paper deals with an energy characterization method of tidal sites. This method is illustrated by the study of a typical tidal site close to the Ouessant (Ushant) Island of the Bretagne region in France. The main objective of this study is to find the optimal location of a tidal turbine including the effect of using or not a yaw drive system. After presenting the different data used in this work, the marine current velocity is first evaluated at different specific locations and times of the studied zone. Afterwords, the tidal energy is evaluated for different systems (tidal turbine with a yaw and bidirectional tidal turbine with fixed axis) and presented in terms of energy distribution maps.

To model currents in a fjord accurate tidal forcing is of extreme importance. Due to complex topography with narrow and shallow straits, the tides in the innermost parts of a fjord are both shifted in phase and altered in amplitude compared to the tides in the open water outside the fjord. Commonly, coastal tide information extracted from global or regional models is used on the boundary of the fjord model. Since tides vary over short distances in shallower waters close to the coast, the global and regional tidal forcings are usually too coarse to achieve sufficiently accurate tides in fjords. We present a straightforward method to remedy this problem by simply adjusting the tides to fit the observed tides at the entrance of the fjord. To evaluate the method, we present results from the Oslofjord, Norway. A model for the fjord is first run using raw tidal forcing on its open boundary. By comparing modelled and observed time series of water level at a tidal gauge station close to the open boundary of the model, a factor for the amplitude and a shift in phase are computed. The amplitude factor and the phase shift are then applied to produce adjusted tidal forcing at the open boundary. Next, we rerun the fjord model using the adjusted tidal forcing. The results from the two runs are then compared to independent observations inside the fjord in terms of amplitude and phases of the various tidal components, the total tidal water level, and the depth integrated tidal currents. The results show improvements in the modelled tides in both the outer, and more importantly, the inner parts of the fjord.

A method of tidal stream energy resource assessment around the Ushant Island in the Iroise Sea, using surface velocity time series from High Frequency radars (HFR) and ADCP measurements, is presented. Remotely sensed velocities provided by the radars allow to augment the industry standard approach of 3D numerical modeling and in-situ ADCP surveying to make a large-scale quantification of tidal stream resource. They capture the real ocean dynamics and thus provide context on the complex spatial variability of tidal currents that are so often feature at potential tidal energy sites. The observations show current velocities of 4 m/s northwest of the Island and in the Fromveur Strait, with 1 m/s value exceeded 60% and 70% of time respectively. Emphasis is given to the peculiarities in tidal flow asymmetry and to the study of the variation of vertical velocity profiles during different tidal stages. Radar derived velocities reveal a pronounced asymmetry between the flood and ebb flow around the Ushant Island, quantified by dimensionless number a - velocity asymmetry. The largest range of asymmetry variation, from 0.5 to 2.5, is observed in the Fromveur Strait. Harmonic analysis demonstrated that a joint variation of phase of the principal semi-diurnal (M2) and quarter-diurnal (M4) tidal velocity component accounts for flow asymmetry variation in the strait. Asymmetry in current direction is also quantified. ADCP measurements show that the vertical velocity profiles follow a 1/α power law with a power law exponent mostly depending on geographic location than on tidal stage. It was demonstrated that, in the Fromveur Strait, the 1/7 power law is appropriate to characterize the velocity profile. The combination of two sources of data enables characterization of the velocity variations in three spatial dimensions and in time thus increasing accuracy of the hydrokinetic resource assessment from HF radar observations. The estimation shows that the mean technical resource is 50% smaller in the lower half than in the upper half of the water column. The theoretical resource on average is three times higher than the technical resource and appears to be more sensitive to variations in the shape of the velocity profile in the lower layer.

The eco-geomorphological development of tidal marshes, from initially low-elevated bare tidal flats up to a high-elevated marsh and its typical network of channels and creeks, induces long-term changes in tidal hydrodynamics in a marsh, which will have feedback effects on the marsh development. We use a two-dimensional hydrodynamic model of the Saeftinghe marsh (Netherlands) to study tidal hydrodynamics, and tidal asymmetry in particular, for model scenarios with different input bathymetries and vegetation coverages that represent different stages of eco-geomorphological marsh development, from a low elevation stage with low vegetation coverage to a high and fully vegetated marsh platform. Tidal asymmetry is quantified along a 4 km marsh channel by (1) the difference in peak flood and peak ebb velocities, (2) the ratio between duration of the rising tide and the falling tide and (3) the time-integrated dimensionless bed shear stress during flood and ebb. Although spatial variations in tidal asymmetry are large and the different indicators for tidal asymmetry do not always respond similarly to eco-geomorphological changes, some general trends can be obtained. Flood-dominance prevails during the initial bare stage of a low-lying tidal flat. Vegetation establishment and platform expansion lead to marsh-scale flow concentration to the bare channels, causing an increase in tidal prism in the channels along with a less flood-dominant asymmetry of the horizontal tide. The decrease in flood-dominance continues as the platform grows vertically and the sediment-demand of the platform decreases. However, when the platform elevation gets sufficiently high in the tidal frame and part of the spring-neap cycle is confined to the channels, the discharge in the channels decreases and tidal asymmetry becomes more flood-dominant again, indicating an infilling of the marsh channels. Furthermore, model results suggest that hydro-morphodynamic feedbacks based on tidal prism to channel cross-sectional area relationships keep the marsh channels from filling in completely by enhancing ebb-dominance as long as the tidal volume and flow velocities remain sufficiently high. Overall, this study increases insight into the hydro-morphodynamic interactions between tidal flow and marsh geomorphology during various stages of eco-geomorphological development of marshes and marsh channels in particular.

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.

The finite volume community ocean model (FVCOM) has been applied to the Ganges-Brahmaputra-Meghna (GBM) delta in the northern part of the Bay of Bengal in order to simulate tidal hydrodynamics and freshwater flow in a complex river system. The delta region is data-poor in observations of both bathymetry and water level; making it a challenge for accurate hydrodynamic models be configured for and validated in this area. This is the first 3D baroclinic model covering the whole GBM delta from deep water beyond the shelf break to 250 km inland, the limit of tidal penetration. This paper examines what controls tidal penetration from the open coast into an intricate system of river channels. A modelling approach is used to improve understanding of the hydrodynamics of the GBM delta system. Tidal penetration is controlled by a combination of bathymetry, channel geometry, bottom friction, and river flow. The simulated tides must be validated before this delta model is used further to investigate baroclinic processes, river salinity and future change in this area. The performance of FVCOM tidal model configuration is evaluated at a range of sites in order to assess its ability to capture water levels which vary over both a tidal and seasonal cycle. FVCOM is seen to capture the leading tidal constituents well at coastal tide gauge stations, with small root-mean-squared errors of 10 cm on average. Inland, the model compares favourably with twice daily observed water levels at thirteen stations where it is able to capture both tidal and annual timescales in the estuarine system. When the river discharge is particularly strong, the tidal range can be reduced as the tide and river are in direct competition. The bathymetry is found to be the most influential control on water levels within the delta, though tidal penetration can be significantly affected by the model's bottom roughness, and the inclusion of large river discharge. We discuss the generic problem of implementing a model in a data-poor region and the challenge of validating a hydrodynamic model from the open coast to narrow river channels.

In this study, the bottom tracking observation in the tidal entrance within Mokpo coast is performed using ADCP in order to estimate net flux of water mass and tidal prism. First of all, observed rawdata was conducted coordinate rotation considering rotation of the cross-section in order to derive the predominant velocity component. And observed rawdata is converted into Sigma coordinate with normalization and blank zone data near the water surface and bottom is interpolated using von-Karman equation. Net flux of water mass is calculated quantitively from the interpolated data, calculated results show that these represent well characteristic of ebb superiority at Mokpo coast as well as change of net flux of water mass with tide. Also, by complementing the definition of tidal prism proposed in past studies, the definition of tidal prism including tidal condition was re-established. Based on the new definition, tidal prism at a tidal entrance using bottom tracking data with ADCP is estimated quantitively for the first time domestically. The results are compared with those for results of previous study, calculated results were in good agreement with previous studies.

The cause of abnormal tidal residuals was examined by analyzing sea levels, sea surface atmospheric pressures, winds at ten tide stations, and current, measured at the coast of the Yellow Sea from the night of November to the morning of the in 2013, along with weather chart. Additionally, the cross-correlations among the measured data were also examined. The `abnormal tidal residuals` mentioned in this study refer to differences between maximum and minium tidal residuals. The largest abnormal tidal residual was identified to be a difference of 176 cm occurring over 4 hours and 1 minute at YeongJongDo (YJD) with a maximum tidal residual of 111 cm and minimum of -65 cm. The smallest abnormal tidal residual was 68 cm at MoSeulPo (MSP) during 8 hours 52 minutes. The cause of these abnormal tidal residuals was not a meteo-tsunami generated by an atmospheric pressure jump but wind generated by the pressure patterns. The flow speed due to these abnormal tidal residuals as measured at ten tide stations was not negligible, representing 16 ~ 41 % of the annual average ebb current speed. From the cross correlation among the tidal residuals, winds, and tidal residual currents, we learned the northern flow, due to southerly winds, raised the sea level at Incheon when a low pressure center located on the left side of the Korean Peninsula. After passing the Korean Peninsula, a southern flow due to northerly winds decreased the sea level.

The present tidal correction of sea level records of Satellite with ARgoes and ALtimeter (SARAL) is based on the finite element solution (FES) of global tide model FES2012 tidal solution. In this study, we examined the validity of the tidal corrections in the coastal oceans around India using tide gauge measurements and a regional tidal model. Our regional model is based on the barotropic version of the Princeton Ocean Model that is forced by the time-varying tidal levels at the open ocean end based on the global FES99 tidal solution. Tide charts prepared from the simulated tidal levels are very similar to the FES tidal solutions. Comparison with the tide gauge measurement shows close agreement with the regional tidal solutions. On the other hand, the agreement with the FES tide models differ significantly in the Gulf of Khambhat and the Gulf of Kutch on the northwest, and in the Hooghly estuary on the northeast continental shelf. However, the agreement is exceptional in other parts of the study d...

International audience; Downscaling physical processes from a large scale to a regional scale 3D model is a recurrent issue in coastal processes studies. The choice of boundary conditions will often greatly influence the solution within the 3D circulation model. In some regions, tides play a key role in coastal dynamics and must be accurately represented. The Bay of Biscay is one of these regions, with highly energetic tides influencing coastal circulation and river plume dynamics. In this study, three strategies are tested to force with barotropic tides a 3D circulation model with a variable horizontal resolution. The tidal forcings, as well as the tidal elevations and currents resulting from the 3D simulations, are compared to tidal harmonics extracted from satellite altimetry and tidal gauges, and tidal currents harmonics obtained from ADCP data. The results show a strong improvement of the M2 solution within the 3D model with a "tailored" tidal forcing generated on the same grid and bathymetry as the 3D configuration, compared to a global tidal atlas forcing. Tidal harmonics obtained from satellite altimetry data are particularly valuable to assess the performance of each simulation. Comparisons between sea surface height time series, a sea surface salinity database, and daily averaged 2D currents also show a better agreement with this tailored forcing.

Potential energy extraction from tidal currents is investigated in this work. Recordings on the streams' velocity and the sea level in the Euripus' strait in Evia, Greece are used to calculate the energy yield. Data on sea level measurements were used to extract information for the current velocity profile through harmonic analysis method. Requirements, limitations and possible new designs that will improve the energy extraction from the low velocity tidal current of the area are discussed. Also, exploitation of tidal energy in cooperation with RES microgrid is proposed for areas where the abundance of sun, wind, island communities and coast areas such as the Mediterranean.

National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore sites around the United Kingdom (UK) for potential tidal stream resource development. A number of prospective tidal energy sites have been identified, but the local hydrodynamics of these sites are often poorly understood. Tidal energy developers rely on detailed characterisation of tidal energy sites prior to device installation and field trials. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal energy development. This paper presents and examines tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), an energetic macrotidal strait, which will soon host Wales' first TST demonstration project. While maximum tidal velocities in the strait during peak spring flood exceed 3 m s−1, the northern portion of Ramsey Sound exhibits a marked flood-dominated tidal asymmetry. Furthermore, local bathymetric features affect flow fields that are spatially heterogeneous in three dimensions, patterns that depth-averaged velocity data (measured and modelled) tend to mask. Depth-averaging can therefore have a significant effect on power estimations. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, variations in the stream flow with depth, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments. In order to fully characterise the structure of the tidal currents, these data should be supplemented with 3-D modelling, particularly in areas subject to a highly irregular bathymetry and complicated tidal regime.

Tidal rivers are intrinsically complex because tidal propagation is influenced by river discharge. This study aims to examine the seasonal variation of tidal prism and energy variance in the tidal river of the Changjiang (Yangtze) River estuary in China. In order to quantify the behaviour of river and tide, we use numerical modelling that has been validated using measured data. We conduct our analysis by quantifying the discharge and energy variance in separate components for both the river and the tide, during wet and dry seasons. We note various definitions of tidal prism and explore the difference between tidal discharge on the flood and ebb and tidal storage volume. The results show that the river discharge attenuates the tidal motion and reduces the tidal flood discharge but the tidal storage volume is approximately constant with different riverine discharge since part of the fresh water discharge is intercepted and captured in the estuary due to the backwater effect. It appears that the tidal discharge adjusts according to the variation of river discharge to keep a constant tidal storage volume. An analysis of the hydraulics shows that the transition from tidal dominance (at the mouth) to river dominance (upstream) depends on the location of tidal current reversal which varies from wet season to dry season. Duringthe wet season, the Changjiang River estuary is totally dominated by energy from fresh water discharge.

The radial tidal current field accounts for the formation of the radial sand ridges in the South Yellow Sea. Understanding the formation and evolution of this radial tidal current field is vital to assessing the morphodynamic features in the area. A semi-enclosed rectangular basin with and without a coastal barrier was schematized from the topography of the Bohai Sea and Yellow Sea. The 2D tidal current field in this basin was simulated using the DELFT3D-FLOW model. The concept of tidal wave refraction, which highlights the effect of the sloped or stepped submarine topography on the propagation of the tidal waves, was introduced to explain the formation of the radial tidal current field. Under the effect of tidal wave refraction, co-phase lines of the counterclockwise rotating tidal wave and incident tidal wave are transformed into clockwise and counterclockwise deflections, respectively, leading to the convergence and divergence of the flow field. Regardless of whether a coastal barrier exists or not, the outer radial tidal current field might emerge over certain topography. The responses of the radial tidal current field in this basin to the environmental variations such as coastline changes and bottom erosions were discussed. Results show that local protrusion near the focal point of the radial tidal current field will have limited effects on the location of the tidal system. However, a remarkable shift of the amphidromic point toward the entrance and central axis of this basin and a movement of the focal point of the radial tidal current field toward the entrance could be caused by the significant seaward coastline advance and submarine slope erosion.

The formation and dynamics of tidal bores in funnel-shaped estuaries is investigated from both a global tidal wave scaling analysis and new quantitative field observations. We show that tidal bore occurrence in convergent estuaries can be estimated from a dimensionless scaling parameter characterizing the relative intensity of nonlinear friction versus local inertia in the momentum equation. A detailed analysis of tidal bore formation and secondary wave structure is presented from a unique long-term database (observations of more than 200 tides) acquired during four campaigns in the two main French tidal-bore estuaries: the Seine and Gironde/Garonne estuaries. We describe the effect of freshwater discharge on the global tidal wave transformation at the estuarine scale and on local tidal bore occurrence in the upper estuary. Our field data suggest that the tidal bore intensity is mainly governed by the dimensionless tidal range, which characterizes the local tidal wave nonlinearity. We also show that the secondary wavefield associated with tidal bore propagating in natural estuaries differs significantly from those associated to undular bores in rectangular channels. In particular, we observe an abrupt decrease of the whelp steepness when the Froude number goes below 1.1. This secondary field transition can explain why tidal bore occurrence in worldwide estuaries is certainly underestimated.

Tidal stream energy is a reliable and predictable low-carbon energy source. Over the next few years the first arrays of multiple tidal stream turbines will be deployed mostly in UK, French and Canadian waters. The potential environmental effects should first be examined, in order to scale and site them appropriately. Large theoretical arrays of tidal stream turbines were designed for Scottish Waters (UK), to quantify the available power and the ocean response to its extraction. A comprehensive assessment of the tidal energy resource realistically available for electricity generation and the study of the potential environmental impacts associated with its extraction in Scottish Waters, can then lead the way to further development in different countries with potential tidal stream energy sources. In order to examine both local ( 100 km) spatial scales, the Scottish Shelf Model, an unstructured grid three-dimensional FVCOM (Finite Volume Community Ocean Model) implementation, is a useful tool, since it covers the entire NW European Shelf, but with a high resolution where the tidal stream energy is extracted. The arrays of tidal stream turbines were implemented in the model using the momentum sink approach, in which a momentum sink term represents the loss of momentum due to tidal energy extraction. A typical annual cycle of the NW European Shelf hydrodynamics was reproduced by the SSM model and compared with the same period perturbed by tidal stream energy extraction. The power extracted by the tidal stream arrays was estimated, taking into account the tidal stream energy extraction feedbacks on the flow and considering the realistic operation of a generic tidal stream turbine, which is limited to operate in a range of flow velocities due to technological constraints. The ocean response to tidal stream power extraction was then analysed at the temporal scale of a spring-neap tidal cycle and, for the first time, on longer term seasonal timescales. It is shown that the very large tidal stream arrays can introduce detectable changes to the tidal elevation, marine currents and ocean stratification patterns. Tidal elevation mainly increases upstream of the tidal farms locations (considering the direction of propagation of the tidal wave), while a decrease in the mean spring tidal range is observed downstream, along the UK East Coast and also in the Irish Sea. Marine currents, both tidal and residual flows, are also affected. They can slow down due to the turbines' action or speed up due to flow diversion and blockage processes, on both a local and regional scale. The strongest signal in tidal velocities is an overall reduction, which can in turn decrease the energy of tidal mixing and perturb the seasonal stratification on the NW European Shelf. Although the strength of summer stratification has been found to slightly increase, the extent of the stratified region does not greatly change, thus suggesting the enhanced biological and pelagic biodiversity hotspots, e.g. tidal mixing front locations, are not displaced. Such large-scale tidal stream energy extraction is unlikely to occur in the near future, since very large numbers of devices are required, but such potential changes should be considered when planning future tidal energy exploitation. It is likely that large scale developments around the NW European shelf will interact and could, for example, intensify or weaken the changes predicted here, or even be used as mitigation measures (e.g. coastal defence) for other changes, e.g. effects of climate change.

The Pará River estuary is a complex and special system in amazon continental shelf, with micro and mesoscale physical processes generated by forces of different sources (e.g., astronomical tides and river discharge). In this study, the main semidiurnal (M2) and the overtide (M4) components were analyzed by quantifying distortions degrees and identifying tidal asymmetries in the Pará River estuary. Two submersible tidal gauges were moored to measure the water level. One on the right margin (point #RG) and another on the left margin (#LF) recorded measurements 6 months (from September 2014 to March 2015). Furthermore, we used harmonic charts from Marine Studies Foundation (FEMAR, Fundação de Estudos do Mar). Lateral variations were also identified between #RG and #LF points from the amplitude and phase cotidal charts, with about 10 minutes delay and variation of 2 cm in tidal amplitude. We verified that the tidal wave enters in system by the right margin (#RF). The results show distortion degrees higher than 10% and positive asymmetry of the tidal wave in the Pará River, and the tidal attenuation in the estuary may be greater than 400 km upstream along the drainage basin.Keywords: Tidal distortion, Tidal asymmetry, Tidal components, Lateral variations.

At least 19 remarkable dikes and land reclamations have been constructed since 1970 along the west coast of Korea, which resulted in a reduction in tidal flat area of almost 50%. Both the reduction in tidal flats and the artificially simplified coastal line have distorted the spatio-temporal tidal hydrodynamics; to quantify this, we analyzed and evaluated tidal asymmetry by phase differences of the principal semi-diurnal lunar constituent M 2 and its first over-tide M 4 . Moreover, we applied the ADCIRC model to quantitatively investigate near- and far-field impacts on tidal variations using the gamma parameter, tidal energy flux, and dissipation rate. Through this study, we found that the tidal regime around the Incheon harbor area in Gyeonggi Bay has changed from ebb- to flood-dominant due to multiple nearby reclamations, in particular to the construction of the Siwha dike. The Saemangeum dike caused near-field de-amplification of M 2 but far-field amplification in the Shandong area of China. In addition to allowing a traditional asymmetry approach using phase difference, analyses based on the gamma parameter and tidal energy variations could distinctly improve spatial understanding of anthropogenic impacts on coastal tidal hydrodynamics.

This study demonstrates a site resource assessment to examine the temporal variation of the current speeds, current directions, turbulence intensities, and power densities for a tidal energy site in the East River tidal strait. These variables were derived from two months of acoustic Doppler velocimeter (ADV) measurements at the design hub height of the Verdant Power Gen5 hydrokinetic turbine. The study site is a tidal strait that exhibits semi-diurnal tidal current characteristics, with a mean horizontal current speed of 1.4 m s−1, and a turbulence intensity of 15% at a reference mean current of 2 m s−1. Flood and ebb flow directions are nearly bi-directional, with a higher current speed during flood tide, which skews the power production towards the flood tide period. The tidal hydrodynamics at the site are highly regular, as indicated by the tidal current time series that resembles a sinusoidal function. This study also shows that the theoretical force and the power densities derived from the current measurements can be significantly influenced by the length of the time window used for averaging the current speed data. Furthermore, the theoretical power density at the site, derived from the current speed measurements, is one order of magnitude greater than that reported in the U.S. national resource assessment. This discrepancy highlights the importance of conducting site resource assessments based on measurements at the tidal energy converter device scale.

In spring 2013, 33 repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K1, O1, M2, S2, and MSf). The ratio of the amplitudes of O1, K1, M2, S2, and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.0±2.1 cm s−1; the associated volume transport through the section is −0.065 ± 0.046 Sv (Sv = 106 × m3 s−1), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.

Predicting tides in upstream reaches of rivers is a challenge, because tides are highly nonlinear and nonstationary, and accurate short-time predictions of river flow are hard to obtain. In the St. Lawrence fluvial estuary, tide forecasts are produced using a one-dimensional model (ONE-D), forced downstream with harmonic constituents, and upstream with daily discharges using 30 day flow forecasts from Lake Ontario and the Ottawa River. Although this operational forecast system serves its purpose of predicting water levels, information about nonstationary tidal-fluvial processes that can be gained from it is limited, particularly the temporal changes in mean water level and tidal properties (i.e., constituent amplitudes and phases), which are function of river flow and ocean tidal range. In this paper, a harmonic model adapted to nonstationary tides, NS_TIDE, was applied to the St. Lawrence fluvial estuary, where the time-varying external forcing is directly built into the tidal basis functions. Model coefficients from 13 analysis stations were spatially interpolated to allow tide predictions at arbitrary locations as well as to provide insights into the spatiotemporal evolution of tides. Model hindcasts showed substantial improvements compared to classical harmonic analyses at upstream stations. The model was further validated by comparison with ONE-D predictions at a total of 32 stations. The slightly lower accuracy obtained with NS_TIDE is compensated by model simplicity, efficiency, and capacity to represent stage and tidal variations in a very compact way and thus represents a new means for understanding tidal rivers.

In the present work, the tidal stream energy in surrounding coastal zones of ZTD is calculated. The tidal current velocity is gotten by three dimensional numerical modeling. The tidal current model is validated by measurement of tidal current observed in 4 points surrounding ZTD. The numerical results given by the tidal current model already shows that: the tidal current velocities given by the model agree with the measured velocities generally. The characteristics of tidal currents around ZTD are analyzed and the following tidal stream energy density is calculated. The maximum tidal stream energy flux of unit width occurs around the middle locations of ZTD southern areas.

[1] Tidal rivers feature oscillatory and steady gradients in the water surface, controlled by interactions between river flow and tides. The river discharge attenuates the tidal motion, and tidal motion increases tidal-mean friction in the river, which may act as a barrier to the river discharge. Time series of tidal water level amplitudes at five gauge stations along the River Mahakam in Indonesia, and tidal flow velocity amplitudes at a discharge monitoring station were obtained applying wavelet analysis. Temporal variations in tidal damping coefficients for quaterdiurnal, semidiurnal, and diurnal tidal species were quantified from the observed amplitude profiles. The analysis shows that tidal damping during the rising limb of a discharge wave differs from damping during the falling limb. Wavelet cross-correlations between surface levels yielded empirical estimates of wave numbers. An empirical relation between tidal damping and river flow is derived to describe subtidal bottom friction along an idealized tidal river resembling the Mahakam. The subtidal friction is decomposed into contributions from the river flow only, from river-tide interaction, and from tidal asymmetry. Even for high river flow and low tidal velocity, river flow enhances friction attributed to river-tide interaction, causing subtidal water level setup. A simple multilinear regression model using subtidal bottom friction is employed to predict subtidal water levels at locations upstream, with a relatively good agreement between predictions and observations. The explicit expression shows the nonlinear dependence of subtidal friction on river flow velocity, explaining the complex behavior of tidal-mean surface level profiles.

A 2D numerical model about the Changjiang Estuary was set up with MIKE 21 in this study, which was well calibrated and verified with the observed tidal levels, flow velocities and flow directions, the computed results agree well with the measured data. Then the model has been applied to calculate the tidal level in the North Branch during spring and neap tide in flood season. The results show that, from the middle reach to the upper reach of the North Branch, the high tidal level is lower and lower and the low tidal level is upper and upper, so the tidal range is decreased, and tidal range during spring is greater than the one during neap. The tidal peak appearing time in the upper reach of the North Branch lags behind that of the middle reach, which is obviously during neap tide. The tidal level curve of the middle reach of the North Branch is smooth and close to the simple harmonic curve, while that of the upper reach of the North Branch deformities, the tidal level curve of ebb tide change fluctuant, much more obviously at spring tide.

A 3-D coastal ocean model with a tidal turbine module was used in this paper to study the effects of tidal energy extraction on temperature and salinity stratification and density-driven two-layer estuarine circulation. Numerical experiments with various turbine array configurations were carried out to investigate the changes in tidally averaged temperature, salinity, and velocity profiles in an idealized stratified estuary that connects to coastal water through a narrow tidal channel. The model was driven by tides, river inflow, and sea surface heat flux. To represent the realistic size of commercial tidal farms, model simulations were conducted based on a small percentage (less than 10 %) of the total number of turbines that would generate the maximum extractable energy in the system. Model results show that extraction of tidal in-stream energy will increase the vertical mixing and decrease the stratification in the estuary. Installation of in-stream tidal farm will cause a phase lag in tidal wave, which leads to large differences in tidal currents between baseline and tidal farm conditions. Extraction of tidal energy in an estuarine system has stronger impact on the tidally averaged salinity, temperature, and velocity in the surface layer than the bottom layer even though the turbine hub height is close to the bottom. Finally, model results also indicate that extraction of tidal energy weakens the two-layer estuarine circulation, especially during neap tides when tidal mixing is weakest and energy extraction is smallest.

[1] Reliable estimation of river discharge to the ocean from large tidal rivers is vital for water resources management and climate analyses. Due to the difficulties inherent in measuring tidal-river discharge, flow records are often limited in length and/or quality and tidal records often predate discharge records. Tidal theory indicates that tides and river discharge interact through quadratic bed friction, which diminishes and distorts the tidal wave as discharge increases. We use this phenomenon to develop a method of estimating river discharge for time periods with tidal data but no flow record. Employing sequential 32 day harmonic analyses of tidal properties, we calibrate San Francisco (SF), CA tide data to the Sacramento River delta outflow index from 1930 to 1990, and use the resulting relationship to hindcast river flow from 1858 to 1929. The M2 admittance (a ratio of the observed M2 tidal constituent to its astronomical forcing) best reproduces high flows, while low-flow periods are better represented by amplitude ratios based on higher harmonics (e.g., M4/M22). Results show that the annual inflow to SF Bay is now 30% less than before 1900 and confirm that the flood of January 1862 was the largest since 1858.

In the process of developing a real-time data-assimilating coastal ocean forecasting system for Prince William Sound, Alaska, tidal signal was added to a three-domain nested model for the region. The model, which is configured from the Regional Ocean Modeling System (ROMS), has 40 levels in the vertical direction and horizontal resolutions of 10.6 km, 3.6 km and 1.2 km for its three nested domains, respectively. In the present research, the ROMS tidal solution was validated using data from coastal tide gauges, satellite altimeters, high-frequency coastal radars, and Acoustic Doppler Current Profiler (ADCP) current surveys. The error of barotropic tides, as measured by the total root mean square discrepancy of eight major tidal constituents is 5.3 cm, or 5.6% of the tidal sea surface height variability in the open ocean. Along the coastal region, the total discrepancy is 9.6 cm, or 8.2% of the tidal sea surface height variability. Model tidal currents agree reasonably well with the observations. The influence of tides on the circulation was also investigated using numerical experiments. Besides tides, other types of forcing fields (heat flux, wind stress, evaporation minus precipitation, and freshwater discharge) were also included in the model. Our results indicate that tides play a significant role in shaping the mean circulation of the region. For the summer months, the tidal residual circulation tends to generate a cyclonic gyre in the central Sound. The net transport into the Sound through Hinchinbrook Entrance is reduced. Tides also increase the mixed layer depth in the Sound, especially during the winter months.

The aim of this study is to understand the effects of friction and advection in the hydrodynamics of a two-inlet coastal lagoon, Santa Maria La Reforma, in Northwest Mexico. A vertically integrated numerical model is used to describe sea level variations and tidal currents, and to study the dynamics inside the system. Observed sea level and current measurements were used to calibrate the model. Results show a ∼90 min phase lag of the tidal signal in the center of the system with respect to both inlets. Tidal currents greater than 1.0 m s −1 were recorded and modeled at both inlets. The sea level in the lagoon shows one-quarter of period of M 2 out of phase (∼3 h) with respect to the velocity. Bottom friction generated the greatest M 4 harmonic and largest tidal asymmetries at the narrowest section of the lagoon, ∼35 km away from the inlets. The tidal momentum balance along the main axis of the lagoon was dominated by pressure gradient and friction, describing a quasi-standing tidal wave in currents and in amplitude. This behavior resulted from waves traveling in opposite directions from the two tidal inlets, causing constructive interference in elevation but destructive interference inflow.

Bathymetric effects on tidal currents are investigated at Main Pass, which is the primary inlet of Mobile Bay, Alabama. A 12-h ship-mounted ADCP survey, which covered nearly one-half of the diurnal tide during flood conditions, included 24 repetitions. The resulting velocity data demonstrate significant tidal variability in the horizontal and vertical current structure between the ship channel and the shoals. The diurnal tidal flows, the dominant tidal forcing, are 72° (4.8 h) ahead of the water level throughout shallower areas of Main Pass, indicating near-standing wave conditions. Moving across the mouth, a phase lag (5.37° or 20 min) develops with the deep channel tidal currents lagging the shoal region. The vertical tidal structure is also modified across the mouth where near-bottom flows change their direction first in the ship channel, while near-surface flows change their direction first over the western shoal. This may be related to the seaward pressure gradient associated with the relatively large (~1715 m 3 /s) freshwater discharge or the discharge interaction with a nearby opening, Pass-aux-Herons. Current magnitudes over the shoals and in the ship channel vary by as much as 1 m/s. Flows at the east side of Main Pass, close to Mobile Point, behave oppositely to those in the rest of the transect during the survey. This inconsistent flow pattern is caused by an anticyclonic eddy that is triggered by flow separation at Mobile Point.

A methodology for assessment of the potential impacts of extraction of energy associated with astronomical tides is described and applied to a site on the Beaufort River in coastal South Carolina, USA. Despite its name, the site features negligible freshwater inputs; like many in the region, it is a tidal estuary that resembles a river. A three-dimensional, numerical, hydrodynamic model was applied for a period exceeding a lunar month, allowing quantification of harmonic constituents of water level and velocity, and comparison to values derived from measurements, recorded at a location within the model domain. The measurement campaign included surveys of bathymetry and velocity fields during ebb and flood portions of a tidal cycle for model validation. Potential far-field impacts of a generic tidal energy conversion device were simulated by introducing an additional drag force in the model to enhance dissipation, resulting in 10–60% dissipation of the pre-existing kinetic power within a flow cross-section. The model reveals effects of the dissipation on water levels and velocities in adjacent areas, which are relatively small even at the 60% dissipation level. A method is presented to estimate the optimal vertical location for the energy conversion device and the potential power sacrificed by moving to a different altitude.

The Sofala Bank, a wide shelf located along the central coast of Mozambique, hosts tides with high amplitudes. The Regional Ocean Modelling System (ROMS) was used to analyse the tidal currents on the bank and to investigate their effects on the stratification and generation of tidal fronts. During spring tides, barotropic tidal currents with maximum values ranging from 40 cm s–1 to 70 cm s–1 are found on the central bank. The major axis of the tidal ellipses for M2 and S2 follow a cross-shelf direction with mainly anticlockwise rotation. Similar to observations, three distinct regimes occur: (i) a warm well-mixed region on the inner shelf where the depths are 30 m. The shelf edge of the bank is important for internal tide generation. Two frontal structures result, one offshore between cooler mixed waters and warmer stratified waters and the other in shallow inshore waters, between cooler mixed waters and solar heated mixed waters.Keywords: barotropic tidal currents, ROMS, sea surface temperature, shallow seas, tidal front

International audience; The influence of the 18.6-year nodal tidal cycle on estuarine accretion, and indirectly on channel migration patterns, in Mont-Saint-Michel Bay, a UNESCO World Heritage Site famous for its monastery, is explored over three tidal cycles from a 68-year dataset that combines aerial photographs (1947–2007), one DGPS survey (1997), and nine LiDAR Digital Elevation Models (2002–2015). Sand-flat elevation and sediment-budget changes in this megatidal environment were further determined over the last nodal cycle using DGPS and LiDAR surveys. We infer that the changes observed are linked to variations in tidal prism and current velocities in this shallow, large tide-range setting. Increasing (rising tidal range) or decreasing (falling tidal range) flood-dominated asymmetry are deemed to lead, respectively, to waxing and waning of sediment import, in the form of large sand banks, into the bay over the 18.6-year nodal tidal cycle that, in turn, force channel migration. Coriolis acceleration and centrifugal forces are also considered to contribute to the observed channel migration.

Holman, R.A. and Stanley, J., 2013. cBathy Estimation in the Mixed Wave-Current Domain of a Tidal Estuary. The last decade has seen considerable progress in the development of algorithms for nearshore bathymetry estimation based on celerity observations of ocean surface waves. This work has evolved into a robust algorithm called cBathy which produces operational results that compared well to 16 CRAB surveys at Duck, NC, collected over two years (bias 0.19 m, rmse 0.51 m over a 1000 by 500 analysis region). However, cBathy is presently based on a wave dispersion implementation that neglects the effects of currents. In May 2012, cBathy was tested in a tidal inlet environment at the RIVET experiment at New River Inlet, NC, a location with a complex ebb tidal delta and strong tidal currents. Initial analyses without Doppler correction to the algorithm show up to 50% overestimation of depth excursions at tidal time scales, presumably associated with wave-current effects. Data from in situ instruments ...

Tidal stream speeds in straits are accelerated because of geographic and bathymetric features. For instance, narrow channels and shallows can cause high tidal stream energy. In this study, water level and tidal current were simulated using a three-dimensional semi-implicit Eulerian-Lagrangian finite-element model to investigate the complex tidal characteristics in the Taiwan Strait and to determine potential locations for harnessing tidal stream energy. The model was driven by nine tidal components (M 2 , S 2 , N 2 , K 2 , K 1 , O 1 , P 1 , Q 1 , and M 4 ) at open boundaries. The modeling results were validated with the measured data, including water level and tidal current. Through the model simulations, we found that the highest tidal currents occurred at the Penghu Channel in the Taiwan Strait. The Penghu Channel is an appropriate location for the deployment of a tidal turbine array because of its deep and flat bathymetry. The impacts of energy extraction on hydrodynamics were assessed by considering the momentum sink approach. The simulated results indicate that only minimal impacts would occur on water level and tidal current in the Taiwan Strait if a turbine array (55 turbines) was installed in the Penghu Channel.

Successful deployment of tidal energy converters relies on access to accurate and high resolution numerical assessments of available tidal stream power. However, since suitable tidal stream sites are located in relatively shallow waters of the continental shelf where tidal currents are enhanced, tidal energy converters may experience effects of wind-generated surface-gravity waves. Waves may thus influence tidal currents, and associated kinetic energy, through two non-linear processes: the interaction of wave and current bottom boundary layers, and the generation of wave-induced currents. Here, we develop a three-dimensional tidal circulation model coupled with a phase-averaged wave model to quantify the impact of the waves on the tidal kinetic energy resource of the Fromveur Strait (western Brittany) - a region that has been identified with strong potential for tidal array development. Numerical results are compared with in situ observations of wave parameters (significant wave height, peak period and mean wave direction) and current amplitude and direction 10 m above the seabed (the assumed technology hub height for this region). The introduction of waves is found to improve predictions of tidal stream power at 10 m above the seabed at the measurement site in the Strait, reducing kinetic energy by up to 9% during storm conditions. Synoptic effects of wave radiation stresses and enhanced bottom friction are more specifically identified at the scale of the Strait. Waves contribute to a slight increase in the spatial gradient of available mean tidal stream potential between the north-western area and the south-eastern part of the Strait. At the scale of the region within the Strait that has been identified for tidal stream array development, the available mean spring tidal stream potential is furthermore reduced by 12% during extreme waves conditions. Isolated effects of wave radiation stresses and enhanced bottom friction lead to a reduction in spring tidal potential of 7.8% and 5.3%, respectively. It is therefore suggested that models used for tidal resource assessment consider the effect of waves in appropriately wave-exposed regions.

The astronomical tide was numerically simulated by the MOHID model for the South-Central Region of Espírito Santo State (Brazil), between latitudes 19.8ºS and 21.2ºS. The grid nesting technique was used to transpose the boundary conditions from the larger domain to a more refined local domain (spatial resolution around 450 m), with tidal harmonics provided by the TPXO tide inverse model as boundary conditions for the larger domain. Results from the numerical model were compared with both the pre-existing tide harmonics and the harmonics calculated from measured data. From the maps of phase, amplitude, tidal ellipses and residual currents the main tidal kinematic characteristics in the study area were described. On the continental shelf, the results showed that the physiography and bathymetry of the region play an important role in the distribution of tidal co-phases, co-amplitudes, ellipses and residual currents. The MOHID model was able to reproduce satisfactorily the astronomical tide and thus can be used to study the behaviour of the tidal propagation in continental shelf areas. Resumo A maré astronômica foi simulada numericamente pelo modelo MOHID para a região Centro-Sul do Estado do Espírito Santo (Brasil), entre as latitudes 19.8ºS e 21.2ºS. A técnica de aninhamento de grades foi utilizada para transpor as condições de contorno do maior domínio para um domínio local mais refinado (resolução espacial de cerca de 450 m), sendo as componentes harmônicas disponibilizadas pelo modelo TPXO utilizadas como condições de contorno para o domínio maior (resolução espacial de cerca de 11,25 km). Os resultados do modelo numérico foram comparados com componentes de maré pré-existentes e com harmônicos calculados a partir de dados medidos. Mapas de fase, amplitude, elipses de maré e correntes residuais foram utilizados para descrever as principais características cinemáticas da maré na área de estudo. Os resultados mostram que a fisiografia e a batimetria da região desempenham um importante papel na distribuição da fase, amplitude, elipses e correntes residuais da maré. O modelo foi capaz de reproduzir satisfatoriamente a maré astronômica, podendo ser utilizado para descrever esse processo em plataforma continental.

Gong, Z.; Wang, Z.B.; Stive, M.J.F.; Zhang, C.K., and Chu, A., 2012. Process-based morphodynamic modeling of a schematized mudflat dominated by a long-shore tidal current at the central Jiangsu coast, China. This paper focuses on the process-based morphodynamic modeling of a mudflat dominated by a long-shore tidal current. The model is schematized as a shore-parallel tidal basin with dimensions similar to the tidal flats near the Wanggang Mouth at the central Jiangsu coast, China. A long-shore tidal current and associated sediment transport are dominant in comparison with their cross-shore components. The mudflat evolution is reproduced for both the case with abundant sediment supply and that with insufficient sediment supply. The simulated flow patterns agree qualitatively with field observations from literature, i.e., involving tidal asymmetry, current directions, and tidal wave features. The analysis of sediment fluxes depicts that deposition occurs from spring tide to neap tide and erosion fr...

We analyze the tidal displacement signals, for the eight major diurnal and semidiurnal tides, from Global Positioning System (GPS) measurements made at the Western United States over the past 16 years with 1075 independent stations. By careful examinations among inland versus coastal GPS data we are able to demonstrate that estimated precisions down to the level of ∼0.1 mm (horizontal) and ∼0.3 mm (vertical) have been reached for the tidal signals, and that at such precisions coherent spatial patterns are revealed in the residual tidal amplitudes and phases after the removal of a priori modeled effects of body tides and ocean tidal loading (OTL). We demonstrate the facility of modern precise GPS data in not only constraining the ocean tide models but, more significantly, in providing source data in terms of regional, complex Love numbers for geophysical inference of the heterogeneities of elastic and inelastic structures in the solid Earth's deep interior on tidal timescales.

International audience; This study shows the short-term sediment dynamics (2010) and the long-term morphological evolution (1905 to 2008) of a tidal sand bar emplaced in the Gironde Estuary, the Plassac Tidal Bar. This tidal sand bar was selected because it corresponds to a morphological category (lobate shape) that was not previously studied in the setting of estuarine bay-head deltas. A recent high-resolution bathymetric survey (2010) evi- dences the sediment transport pattern, inferred from the lee face orientation of subaqueous dunes. This sediment transport pattern, together with results from previous studies, explains the five main mechanisms for the tidal bar evolution identified from 29 bathymetric maps since 1905: namely, flood ramp infill, partial ebb shield breaching, lateral accretion of the ebb spits and ebb shield lengthening, generated by the merging of mini-flood lobes on the outer sides of the ebb spits. Lateral accretion seems to be a key-process of sediment accretion for lobate tidal sand bars. Most of the evolutions are explained by tidal processes, but a fluvial influence is evidenced by correlating the presence of mini-flood lobes (migrating seaward from the upper reaches of the bay-head delta) and the lengthening of the tidal bar with periods of high fluvial discharge. A ca. 25-year periodicity in both the fluvial discharge and the tidal bar width, length and volume variations is evidenced and suggests a climate control on the tidal bar evolution. A classification of lobate tidal sand bars is proposed in order to distinguish tide-dominated and wave-influenced sand bars emplaced in large estuary mouth or tidal inlets, from tide-dominated and fluvial-influenced sand bars emplaced in bay-head deltas.

Shelf tidal stream velocities are accelerated by nearshore geographic features, such as headlands and islands. In the search for sustainable forms of electrical energy generation, such locations may become attractive for tidal stream power developments. For some prospective tidal stream energy sites, however, little is known about the intricacies of the local tidal dynamics: knowledge which is crucial to the understanding of the resource and the potential environmental consequences of its extraction. In this paper a two dimensional hydrodynamic model is used to investigate a complex tidal strait, the Pentland Firth (Scotland, UK). This channel, considered one of the most promising tidal stream energy sites in the world, is set for extensive development over the coming decade. We show that the tidal stream velocities that regularly occur within, and up to 20-km beyond the Pentland Firth, are accelerated above that of a free shallow-water wave. The primary mechanism for these accelerations is hydraulic in nature, associated with a large shift in tidal phase. Tidal streaming around headlands and islands further promotes conversion from potential to kinetic energy. We calculate a mean energy flux into the Pentland Firth from the North Atlantic Ocean of 8.97 GW. Changes in tidal amplitude and phase along the strait are associated with a reduction in energy flux, such that the majority (∼60%) of the incoming energy is lost within the Pentland Firth through bed friction. Localised geographical factors complicate the tidal dynamics of the Pentland Firth, therefore detailed modelling is the only means with which to accurately characterise the environmental conditions in this channel. Of more general oceanographic significance, this example shows that high levels of tidal energy dissipation are associated with energetic tidal straits. Energy losses in these straits may contribute significantly to balancing the energy flux onto the continental shelf from the deep seas.

The surface M2 tide in the Canadian Arctic Archipelago (CAA) is reproduced on the basis of the QUODDY�4 threedimensional finiteelement hydrodynamic model. Particular emphasis has been placed on comparing model estimates for the amplitudes and phases of tidal elevations and the parameters of ellipses (major semiaxis and eccentricity) of the barotropic tidal current velocity with observational data. We present their spatial distributions and the distributions of averaged (over a tidal cycle) values of the density, horizontal transfer, and dissipation rate of barotropic tidal energy. It is found that the CAA is a much less effective dissi� pator of barotropic tidal energy than the World Ocean.