Search

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.

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.

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.

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.

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.

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 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.

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.

Tidal asymmetry is a key factor in the geomorphology of many coastal lagoons. Whilst tidal asymmetry in semi-diurnal tidal regimes has been extensively studied, its occurrence in mixed tidal regimes is less well understood, and has a number of unique causes and characteristics. Tidal phase duration analysis and least squares harmonic analysis have been used to study the temporal and spatial nature of asymmetry in both offshore and coastal lagoon tides at the Murray Mouth in south-eastern Australia. GIS analysis of bathymetric survey data has been used to study the roles of lagoon bathymetry on tidal distortion. Tidal asymmetry in the Murray Mouth coastal lagoon results from frequency relationships between major astronomical driving tides as well as bathymetry-induced tidal transformations. The frequency difference between the K1 and S2 tides produces an important 6-monthly ebb/flood-dominant asymmetry cycle in the incoming oceanic tides, whilst phase relationships between the K1 and K2 tides contribute to persistent asymmetry. The use of standard relationships between the M2 and M4 tides as asymmetry indicators is shown to be invalid for this mixed tidal regime. In this shallow, microtidal system, the impacts of bathymetry on tidal asymmetry within the lagoon are profound, with inlet and channel configurations identified as the most important controlling factors. The results of this study may inform the strategic management of tidal inlets in mixed tidal regimes, such as the Murray Mouth, that are subject to intermittent or long-term constriction.

Tidal stream turbines are exploited in regions of high tidal currents. Such energy extraction will alter the hydrodynamics of a tidal region, analogous to increasing the bed friction in the region of extraction. In addition, this study demonstrates that energy extracted with respect to tidal asymmetries due to interactions between quarter (M4) and semi-diurnal (M2) currents will have important implications for large-scale sediment dynamics. Model simulations show that energy extracted from regions of strong tidal asymmetry will have a much more pronounced effect on sediment dynamics than energy extracted from regions of tidal symmetry. The results show that energy extracted from regions of strong tidal asymmetry led to a 20% increase in the magnitude of bed level change averaged over the length of a large estuarine system, compared with energy extracted from regions of tidal symmetry. However, regardless of the location of a tidal stream farm within a tidal system, energy extraction reduces the overall magnitude of bed level change in comparison with non-extraction cases. This has practical application to many areas surrounding the UK, including the Irish Sea and the Bristol Channel, that exhibit strong tidal currents suitable for exploitation of the tidal stream resource, but where large variations in tidal asymmetry occur.

Tidal circulation and river plume dynamics in shallow-water estuarine systems with large intertidal zones are complex. Strong asymmetries in tidal currents and stratification often occur in the intertidal zones and subtidal channels over a tidal cycle. The Skagit River is the largest estuary with respect to the discharge of a significant amount of freshwater and sediment into Puget Sound, Washington. It consists of a large intertidal zone with multiple tidal channels near the mouth of the estuary. To simulate the tidal circulation and salinity stratification accurately in the intertidal region, an unstructured grid numerical model with wetting–drying capability and the capability to accurately represent the bathymetry of tidal flats and the geometry of shallow distributary channels is necessary. In this paper, a modeling study for the Skagit River estuary using a three-dimensional unstructured grid, finite-volume coastal ocean model (FVCOM) supported by high-resolution LIDAR data is presented. The hydrodynamic model was validated with observed water surface elevation, velocity, and salinity data over spring and neap tidal cycles under low-river-flow and high-river-flow conditions. Wetting and drying processes in the intertidal zone and strong stratification in the estuary were simulated successfully by the model. Model results indicate that the Skagit River estuary is a highly stratified estuary, but destratification can occur during flood tide. Tides and baroclinic motion are the dominant forcing in the Skagit River estuary, but strong wind events can affect the currents in the intertidal zone significantly. Preliminary analysis also indicated that the salinity intrusion length scale is proportional to the river flow to the −¼ power.

Tidal currents within many estuaries are stronger than on the adjacent continental shelf. Estuarine tidal influence extends onto the shelf elevating tidal amplitudes above ambient shelf levels over a region outside the estuary. In this paper, a kinematic theory that describes tidal flow in these estuary–shelf tidal interaction zones is derived and tested. Using these results, tidal current amplitudes outside estuaries are estimated and the range and intensity of estuarine tidal influence is characterized. The estimates for the tidal current amplitudes (utide) of the dominant constituent are appropriate for linear or weakly nonlinear systems with predominantly barotropic tides; the ratio of tidal height to water depth is small (η/h≪1) in linear or weakly nonlinear regimes. Within tidal interaction zones, the tidal current amplitude is composed of an ambient shelf part (ua) and an estuary-induced part (ue). The characteristic shelf amplitude far from the estuary is used to set ua. Continuity arguments indicate that ue (averaged over a control volume arc centered on the mouth with radius r and a swath angle of γπ) approximately equals the ratio of the tidal volume flux through the mouth (Vm) and the cross-sectional area of any control volume arc ( u e ≈ V m / γ π r h ¯ ) . This approximation holds where the squared product of the tidal wave number and radial distance is small: (kr)2≪1. For a shelf with constant slope α and small coastal wall depth, the arc-averaged depth is h ¯ ≈ sr (where s=2α/pi for γ=1). For this shelf bathymetry, ue decays with squared radial distance from the estuary mouth. Theoretical predictions are consistent with observed tidal current amplitudes outside the Delaware Bay and Block Island Sound. In both test cases, the estimated and observed amplitudes exhibit an r−2 dependence and decay over a similar distance. The relative importance of estuarine tidal influence is assessed with the tidal interaction index (Ti=ue/ua). The intensity of estuarine influence is characterized by the value of Ti at the mouth (Tim). The extent of an estuary–shelf tidal interaction zone is measured by the interaction radius ri (where Ti=1) and by r∞ (where Ti=0.1). These metrics are used to compare the tidal interaction zone characteristics for the Delaware Bay, Block Island Sound, several other major estuaries, and a small tidal inlet. The kinematic theory can be applied outside other estuaries where only limited tidal information is available or used to interpret observed patterns in tidal amplitudes and characterize the degree of estuarine influence.

In this paper, we analyse the contribution of tidally induced drift in the surface layer to the overall dynamics of well-mixed tidal basins undergoing drying and flooding. The study area covers the East Frisian Wadden Sea (German Bight, Southern North Sea), which consists of seven tidal basins. The major interest is focused on the tidal basin behind the islands of Langeoog and Spiekeroog and the inlet connecting it with the North Sea. The comparison between theoretical concepts, results from direct observations, and simulations with a numerical model helps to understand the underlying physics controlling the tidal response. The data were collected during the period 1995–1998 and consist of cross-channel ADCP transects. The identification of the dominant spatial patterns and their temporal variability is facilitated by applying an EOF analysis to the data. The numerical simulations are based on the 3-D primitive equation General Estuarine Transport Model (GETM) with a horizontal resolution of 200 m and terrain-following vertical coordinates. We find distinct differences between the temporal variability of the transports near the surface and those in deeper layers of the tidal inlets. The near surface transport is dominated by the tidally induced drift (similar to the Stokes drift), whereas the deeper layer transport is dominated by asymmetries caused by the hypsometric properties of the intertidal basins. These transports, when averaged over a tidal period, have opposite directions and compensate each other. This explains the establishment of a vertical overturning cell: landward motion in the upper layers and seaward motion in the deeper parts of the tidal channels. This vertical circulation cell is also observable in our numerical simulations and shows a clear dependency of the temporal asymmetry in the transport patterns on the local depth. In deep tidal channels, the overall properties of the tidal signal show a clear ebb dominance, whereas in the shallow extensions of the channels the transports during flood are larger than during ebb. Although, our research area can be characterized as a well mixed estuary, baroclinicity associated with the fresh water flux from the coast can substantially affect vertical overturning.

A three-dimensional, primitive-equation model is used to simulate the barotropically-forced semidiurnal tidal currents in the New York Bight (NYB) and Block Island Sound (BIS). Model tidal velocity ellipses are verified at historical current meter locations and with measurements from acoustic Doppler current profilers (ADCPs) and HF radar (CODAR). The model reproduces well the regional tidal flow pattern as well as the vertical tidal velocity structure. The model misfits typically are 2–4 cm/s in amplitude and 5–7° in orientation. Through comprehensive skill assessment, the model's capacity of simulating the three-dimensional barotropic tidal currents is clearly demonstrated. Moreover, it is shown that the integrity of HF radar measurements can be assured by verifying with model tidal ellipses.

Tidal energy flux and dissipation in the Chesapeake Bay are examined using a three-dimensional baroclinic model. The model currents are validated by a comparison with observed tidal current ellipses collected during previous field surveys. The model elevations are validated against sea-level records collected at tidal gauges. The baroclinic model produces more accurate predictions for sea-level heights and tidal currents than the tidal models which do not consider the effects of stratification. The averaged rms differences between the observed and modeled surface elevations are 3.4 cm for the M2 constituent and 0.7 cm for the K1 constituent. The averaged rms differences between the observed and modeled tidal current ellipses are 2.6, 2.1 cm s−1, 5.1° and 21.7° for the semi-major, semi-minor axes, inclination and phase of the ellipses, respectively. The total amount of tidal energy flux entering the Bay mouth is found to be 188 MW, 88% of which is associated with the M2 component. Dissipation of tidal energy is highly non-uniform in the Chesapeake Bay. 40% of the energy dissipation occurs in four topographic hotspots: the Bay mouth region around the headland of Delmarva Peninsula, the region near the Rappahannock sill, the constriction near the Bay Bridge and the constriction north of Baltimore.

A s-coordinate three-dimensional model, regional ocean modeling system (ROMS), was implemented in the Western Iberian region ranging from the coast to 11°W aiming high-resolution tidal simulations for an homogeneous ocean. The features for tidal heights and ellipses for the principal constituents, M 2 , S 2 , N 2 , K 2 , K 1 , O 1 , P 1 and Q 1 , were imposed at the boundaries of the model. A tidal analysis for heights and tidal currents was done allowing to calculate two-dimensional distribution of amplitudes and three-dimensional structure of tidal currents. The amplitudes and phases for heights agree with previous results and observations, showing a good precision on the tidal propagation in the interior of the domain. Tidal kinetic energy is dominated by the semi-diurnal components, mainly M 2 , and increases on the shelf. Over the Lisbon Promontory the diurnal component K 1 is however the second more energetic harmonic. Vertical variation of tidal ellipse parameters evidences the different structure of semi-diurnal and diurnal tidal components, as well as differences between the open sea and shelf tidal circulation.

Portland Bill (Dorset, UK) is a promising site for tidal stream energy exploitation; it combines high tidal stream velocities around the headland with a location closer to population centres than other proposed sites. To better estimate available energy resources at the site, a two-dimensional tidally driven hydrodynamic numerical model of Portland Bill was developed using the TELEMAC system, with validation using tidal elevation measurements and tidal stream diamonds from Admiralty charts. The results of the model were used to produce a time series of the tidal stream velocity over the simulation period and may be used in future work to optimize the location of turbine arrays at the site.

The tidal characteristics of Maputo Bay (a bay located in South part of Mozambique) were assessed in this work through the implementation of a numerical model (SIMSYS2D) and exploration of its numerical results, and by the analysis of observed time series of free surface elevations in Maputo Harbor. The calibration of the numerical model was carried out based on time series of tidal currents and free surface elevation, which were collected at Maputo Harbor, Baixo Ribeiro and Portuguese Island. By means of the model results, important harmonic constants of the tidal heights and currents, as well as the form factor, were computed. These results have revealed that there is a phase delay and an increase in amplitude of the major constituents as the tide propagates to the inshore zone. Based on these results, the tidal ellipses in whole Maputo Bay were also computed, which showed the pattern of the tidal currents. The hydrodynamics of the Maputo Bay under extreme tidal conditions were also analyzed (during the largest spring tide and smallest neap tide). The phase difference between tidal heights and currents revealed that there are no maximum fluxes of energy in most of Maputo Bay and that the mean tidal current (residual) may be different from zero in this system.

A non-linear hydrodynamic model is used to describe the tidal dynamics of Shark Bay, Western Australia. The model is forced by tidal elevations generated by M 2 , S 2 , K 1 and O 1 constituent data at the open boundaries. The absence of suitable boundary data required a ‘calibration’ of the boundary condition against the known constituent data from within the model domain. The model provides a good match to the available field data, and allows the surface-level and current response to be resolved over the entire domain. Due to a near quarter-wave resonance of the semi-diurnal tide along the eastern Hopeless Reach, which increases the semi-diurnal tide by a factor of 2, the tidal characteristics on each of the Reaches are different: on the eastern Hopeless Reach the tides are mainly semi-diurnal while on the western Freycinet Reach the tides are mainly diurnal. The tidal range is also higher along Hopeless Reach. Tidal harmonics, generated by non-linearity, are important in the shallow regions. The tidal wave is shown to propagate as a progressive wave into the Bay. Substantial phase-lag, attenuation and dissipation occur over the Faure Sill, a major shallow region of the eastern reach of the Bay. Non-linear generation of the M 4 and MS 4 tides is also significant in this region. Depth-averaged residual currents are presented, which show a tidally generated circulation that is enhanced in regions of complex topography. Estimates of tidal dissipation indicate that although the total dissipation is small on a global scale, the areal average is comparable with the Gulf of Carpentaria and approximately one-quarter of the value estimated for the Patagonian Shelf.

A 3D finite-element numerical model is applied to the Adriatic Sea to simulate its tidal motions. This fully nonlinear model includes a free surface, very realistic topography, and an advanced turbulence closure. Comparison with available tidal elevations at coastal stations and with tidal ellipses at a few locations in the open sea demonstrates that the model simulations are highly accurate. The results are then used to determine the 3D distribution of the tidal residual currents. D 2002 Published by Elsevier Science B.V.

We examine tidal asymmetry in a 100-km long coastal plain estuary, a 15-km long tidal creek closed at the end, and a small side channel of a coastal plain estuary closed at low water. Current meter and water depth data were harmonically analyzed for M2 and the M4 and M6 overtide. The results are displayed in a plot of tidal current versus water level and the effects of the M2, M2+M4, and M2+M4+M6 are compared in order to show how overtides affect tidal asymmetry in the different systems. The long estuary showed a gradual increase in tidal current asymmetry. The current takes on a more progressive nature as it goes into the estuary, as indicated by increasing lags between high or low water and the corresponding slack water. On the other hand, the tidal creek has its reflection point at the head, a relatively short distance from the observations, which reflects the incident tidal wave more efficiently. The tidal creek has a high salt marsh which is covered only an hour or so before high water. Since its intertidal areas flood and drain near the time of high water, maximum flood and ebb currents occur a short time before and after high water slack throughout the tidal creek. Most of the tidal energy is dissipated at the end of the creek where M6/M2 of the tidal current almost doubles. The small side channel has tidal flats that become covered soon after the time of low water. The relative time of maximum flood and ebb currents occurs much closer to the time of low-water-slack, which contrasts significantly to the timing in the tidal creek channel surrounded by high salt marsh.

Using the CSR4.0 global ocean tidal model and the local ocean tidal maps of China Seas, we calculated the ocean tidal displacement corrections for the Earth Crust Movement Network of China. We also discuss the effect on the corrections caused by the tidal model and Green's function. As an actual example, we used the GPS observational data to estimate the influence of ocean loading tides on the GPS baseline vectors. Our results show that the corrections of ocean loading tide for the site displacement of geodetic stations and the variation of GPS baseline vector may reach maximum values of about 2 cm and 2 mm, respectively.

Candela et al. (1990, 1992) showed that tides in an open ocean region can be resolved using velocity data from a ship-mounted ADCP. We use their method to build a spatially varying model of the tidal currents in the Gulf of the Farallones, an area of complicated bathymetry where the tidal velocities in some parts of the region are weak compared to the mean currents. We describe the tidal fields for the M 2 , S 2 , K 1 , and O 1 constituents and show that this method is sensitive to the model parameters and the quantity of input data. In areas with complex bathymetry and tidal structures, a large amount of spatial data is needed to resolve the tides. A method of estimating the associated errors inherent in the model is described.

The purpose of this paper is to determine, with the aid of a two-dimensional model, the depth-averaged tidal stream in the south-west lagoon of New Caledonia. A description based on field data is given first. Coastal sea level and open-sea data (bottom pressure, currents) are harmonically and spectrally analysed. The first-order dynamics of this lagoon are dominated by semi-diurnal tides. Except for the passes, diurnal tides and currents are weak, only the two tidal harmonics M 2 and S 2 are subsequently investigated. A numerical model is used to provide a coherent and dense picture of the tidal dynamics of M 2 and S 2 and their variability. The validity of the model is assessed by comparing its results with measured sea level and current data. Amplitudes and phase-lags of the M 2 tide increase from south to north. M 2 currents are maximum in the south and in the passes. S 2 amplitudes increase from south to north but slower than M 2 . S 2 phases spread from north-west to south-east. Using model results, the long-term movement of the water mass due to tidal influence is estimated by calculating the residual Lagrangian velocity.

The evolution of tidal basins greatly depends on the interaction between the tide and basin morphology. This interaction results in deformation of the tidal wave which can change the tidal flow, and thus the sediment transport, at the basin inlet. However, this tidal distortion inside tidal basins is complex and cannot be deduced directly from the basin morphology, especially in the case of large basins. Therefore, the reliability of reconstruction of tide deformation in ancient basins with limited topographical information by using a one-dimensional numerical flow model was studied. Two former, historical situations of the Scheide estuary, 1800 AD and 1650 AD, were chosen as a test case. It is shown that for both situations known information on tidal range and phase of the tidal wave is reproduced reasonably well by the model. Since 1650 the tidal flat surface area in the Schelde estuary was strongly reduced. Simultaneously, the channel depth increased. These changes in basin geometry caused an increase in tidal celerity in the estuary. At the mouth, the maximum ebb current velocity increased relative to the maximum flood velocity. If tidal-current asymmetry at the estuary mouth is considered as a measure for net sand transport into the estuary, the simulations indicate a decrease in net basinward sand transport in reaction to the morphological changes in the estuary.

The tide-related parameters of the Delaware Bay are derived from Space Shuttle time-series photographs. The water areas in the bay are measured from interpretation maps of the photographs with a CALCOMP 9100 digitizer and ERDAS Image Processing System. The corresponding tidal levels are calculated using the exposure time annotated on the photographs. From these data, an approximate function relating the water area to the tidal level at a reference point is determined. Based on the function, the water areas of the Delaware Bay at mean high water (MHW) and mean low water (MLW), below 0 m, and for the tidal zone are inferred. With MHW and MLW areas and the mean tidal range, we calculate the tidal influx of the Delaware Bay, which is 2.76 x 10 exp 9 cu m. The velocity of flood tide at the bay mouth is determined using the tidal flux and an integral of the velocity distribution function at the cross section between Cape Henlopen and Cape May. The result is 132 cm/s, which compares well with the data on tidal current charts.

An array of one-dimensional models has been used to simulate the vertical structure of tidal currents and temperature of the North Sea with a 37 km (20 nautical mile) grid. The model, which is based on the Mellor and Yamada (1974) Level 2 turbulence closure scheme, includes meteorological fluxes at the surface and tidal stirring at the bottom. Depth-varying tidal currents were predicted using pressure forces derived from a depth-averaged tidal model. The model was driven using meteorological fluxes supplied by an atmospheric forecasting model and the results compared with CTD measurements collected during 1989.

We analysed the tidal content of current time series from 53 current meters at 31 mooring locations on the inner continental shelf in the vicinity of Delaware Bay, U.S.A. We distinguish between an astronomically forced short period flow field at diurnal and semi-diurnal frequencies and a nonlinearly generated long period tidal flow field. The latter operates at the difference frequencies of the former. We found short period tidal currents to vary from 90 cm s−1 at the mouth of the estuary to 8 cm s−1 only 30 km to the north. Tidal volume flux through the mouth generates intensified tidal currents on the shelf as far as 50 km away to the southeast. At periods longer than 2 weeks we detected tidal currents with amplitudes from 1 to 3 cm s−1 and phases indicative of a horizontally coherent flow field. We also estimated mean rectified tidal flow fields of about 2–7 cm s−1. These thus contribute substantially to the overall mean currents on the shelf.

Tidal jets are a ubiquitous feature of the coastal environment and result from strong tidal streaming off coastal features such as promontories. Around the Isles of Scilly there exist two tidal jets which tend to propagate in a clockwise sense around the island group. Currents in excess of 90 cm s−1 appear necessary for their production and the jets are characterized with a Reynolds number of about 30. It is shown that the jets indicate the direction of the maximum stream and the residual circulation around the islands. With an offshore component to the residual flow, tidal fringes may develop from the jets and such fringes were observed on the northern side of the islands.

A two-dimensional numerical model, which includes tidal basins in the western Dutch Wadden Sea and a part of the adjacent North Sea, is used to study tidal and tidally-driven residual flows and elevations. The model is verified by comparing observed and computed water elevations in some stations and transport rates through the tidal inlets. The consequence of topographical and geometrical differences for the terms in the governing equations is discussed by comparing the magnitude of these terms in some characteristic grid points, viz. the open sea, inlet and basin channel, in which all terms are decomposed along and perpendicular to the dominant current direction. Averaging over a tidal period shows that compared to the time-dependent equations an important shift takes place in the relative influence of the different terms, mainly caused by the increased influence of the advective term. The resulting tidally-driven residual flow field is interpreted as a combination of a constant volume transport (1 to 2% of the tidal transport in the tidal inlets) between connected tidal basins and isolated residual eddies (with velocities of 10 to 15% of the tidal velocity amplitude and a typical length scale of between 3 and 10 km). Observations confirm that the drop in residual elevations in tidal inlets and the rise in tidal basins are phenomena characteristic of all tidal basins.

The general tidal characteristics in the neighbourhood of a promotory are derived using a numerical model developed in plane polar coordinates. These same tidal features are found for a model of the tides off the Start Point promontory using a Cartesian reference frame. It is shown that promontories are characterised by strong tidal flows and it is suggested that vorticity generated near the headland plays a key role in the dynamics of offshore tidal bank formation.

Numerical modelling of M 2 tidal streams in the Celtic Sea with a sea level lowered by 100 m indicates tidal currents about twice as strong as those at present. Such currents would have been sufficient to generate and maintain the linear tidal sand banks now found in that region as moribund bedforms. Furthermore, an indicated clockwise rotation of the major axes of the tidal ellipses at a sea level lowered by 100 m with respect to the present day is in the correct sense to further the comparison with modern examples of actively maintained linear tidal sand banks.

Previous work on tidal dynamics in salt marsh creeks have shown that velocity and discharge exhibit well marked surges throughout the cycle as well as a flood-ebb asymmetry. Two general models of tidal dynamics are discussed: one assuming modification of tidal stage by the marsh channel, the second assuming that channels have a purely passive role. Using the second model a series of theoretical velocity curves are calculated using progressively more complex tidal approximations. The theory is tested using velocity data obtained from the Stiffkey marsh, N. Norfolk, England by Bayliss-Smith et al. (1978). The velocity curve can be predicted using channel morphometric and tidal stage data. The interaction between channel morphology and the velocity curve are considered: it is suggested that channel velocity curves may provide an indication of marsh morphological development.

A 349-day series of consecutive hourly readings from a single current meter mooring in the deep water of the Weddell Sea was analysed to determine the tidal currents. Amplitudes and Greenwich phase-lags were found for both the east-going and north-going components of velocity for the eight principal harmonic constituents. Constituents tidal ellipses were drawn for the four most energetic constituents O 1 , K 1 , M 2 , and S 2 ; the current vectors rotated clockwise in each case. Analysis of each successive quarter of the time series yielded results consistent with those from analysis of the entire record. The amounts of barotropic and baroclinic energy in the diurnal and semidiurnal tidal bands are consistent with the barotropic nature of circulation in the Weddell Sea.

The generation of tidal asymmetries is clarified via numerical integration of the one-dimensional equations for channel geometries characteristic of shallow estuaries. Channels without tidal flats develop a time asymmetry characterized by a longer falling than rising tide. This behavior is enhanced by strong friction and large channel cross-sectional area variability over a tidal cycle. Resulting tidal currents have a shorter, intense flood and a longer, weak ebb (flood-dominant). Addition of tidal flats to the channels can produce a longer rising tide and stronger ebb currents (ebb-dominant), if the area of tidal flats is large enough to overcome the effects of time-variable channel geometry. Weaker friction with flats can also produce this asymmetry. Despite the physical complexity of these systems, essential features of estuarine tidal response can be recovered from one-dimensional models. Shallow estuaries are shown to have a system response leading to stable, uniform senses of tidal asymmetry (either flood- or ebb-dominated, due to phase-locking of forced tidal constituents), with down-channel development in magnitude of asymmetry. These concepts are illustrated by modeling idealized representations of tidal channels at Nauset Inlet, MA, and Wachapreague Inlet, VA, which have flood- and ebb-dominance, respectively.

The importance of asymmetric tidal cycles in the transport and accumulation of sediment in shallow well-mixed estuaries is well established. Along the U.S. Atlantic Coast, tidal amplitude, bottom friction, and system geometry determine tidal distortion as documented at 54 tide gauges in 26 tidally dominated estuaries of varying geometry having negligible freshwater inflow. Analyses of sea-surface heights are compared to the results of one-dimensional numerical modelling to clarify the physics of tidal response in well-mixed estuaries. Concise measurements of estuarine geometry and ocean tidal range are used to predict consistently the nature of tidal sea-surface distortion. Numerical modelling then is utilized to extend theoretical and observational relationships between geometry and sea-height to predict trends in velocity distortion and near-bed sediment transport. Non-linear tidal distortion is a composite of two principal effects: (1) frictional interaction between the tide and channel bottoms (reflected in a h = tidal amplitude channel depth ) causes relatively shorter floods; (2) intertidal storage (measured by V s V c = volume of intertidal storage volume of channels at mean sea level) causes relatively shorter ebbs. Variations in V s V c and a h trigger consistent and predictable changes in tidal distortion as measured through the first harmonic of the principal tidal constitutent.

Observations at 8 sites in the outer central Great Barrier Reef show M 2 , S 2 , K 1 , and O 1 tidal currents flow directly off-shelf (northeast), when the corresponding tide at Townsville is at zero height and falling, with typical amplitudes of 12, 6, 3, and 2 cm s −1 . On the slope (at 300 m depth), the vertically averaged long-shelf component was small. On the shelf, the eccentricity of the tidal ellipses decreases shoreward and the tidal ellipses rotate anticlockwise. The major axes of the tidal ellipses tilt left of cross-shelf, especially for the diurnal constituents. There is satisfactory agreement between the observed and modelled cross-shelf currents. The long-shelf velocity is sensitive to the long-shelf changes in amplitude and phase of the tide heights and high quality tidal data for open boundary conditions will be required if numerical models are to model these currents satisfactorily.