Tidal Current Model Research Articles

Effects of the Large-Scale Reclamation Project on Hydro-Dynamic Environment in the Estuary

The hydro-dynamic environment will be changed after reclamation project building. It will affect the navigation, estuary regime, tidal prism, flood controlling, storm surge and so on. Taking the shore reclamation between Oujiang and Feiyunjiang estuary as example, a tidal current mathematical model is used to study the effects of the large-scale reclamation on the hydro-dynamic environment. Based on triangle grid and finite volume method, the shallow flow model is examined by 9 tidal level stations and 9 observed synchronous vertical lines. And the comparison between computed result and measured solution demonstrates very good agreement. After the project building, the high tide level reduces to a certain extent and the flow of front reclamation line reduces by a big margin. But it is a little influence to the core ports of Wenzhou. And the tidal influx through Feiyunjiang Estuary decreases. The result can provide important reference and inspiration for the effects of hydro-dynamic environment due to the large-scale reclamation projects.

Numerical Simulation of Heavy Metal (Pb) Distribution in Luoyuan Bay Based on Tidal Current

Compared with the data measured by other ones, the concentration of heavy metal (Pb), which is investigated by us in July 2011, has increased significantly in Luoyuan Bay, especially near Baishui Zone. The main reason is the discharged waste water from some recently founded large-scale steel plants around Luoyuan Bay. A numerical tidal current model in Luoyuan Bay is established based on FVCOM, with which a heavy metal transport model is developed to simulate the distribution of Pb discharged from steel plants.Reasonable agreement between the model results and field data has been obtained, indicating that the numerical model can be used as computational tool for environment management and the prediction of heavy metals in Luoyuan Bay.

Spatio-temporal variability of currents over a mobile dune field in the Dover Strait

A one month field campaign featuring two spring–neap tide cycles and three strong storms has been performed in a mobile dune area located in the central part of the Dover Strait. These dunes are known to move in a complex manner as their migration direction varies in space and time ( Le Bot and co-workers, 2000, 2001, 2004). In order to gain some insights into the dune motion processes we present an analysis of the spatio-temporal variability of currents in the area emphasizing the relative influence of tides and storms. A total of eight different hydro-meteorological regimes have been distinguished during the experiment duration. The analysis of the currents measurements at five locations in the area shows that the eight hydro-meteorological regimes induce very different current responses at the bottom. The residual tidal currents exhibit a significant spatial variability both in direction and in intensity. A numerical model of tidal currents over the Dover Strait confirms the strong spatio-temporal variability of the residual tidal currents featuring three singular points. Amongst them, a saddle point is located just south of the I-dune at the convergence of opposite direction residual tidal currents. The wind-induced currents are almost uniform in space, their intensity and direction however strongly depends on the wind regime and thus on time. The mean total current feature a spatial pattern which can be tidal of wind-induced currents dominated, or either in balance, depending on the regime considered. At the PERMOD campaign time scale, the total current is dominated by the residual tidal current. These results proved to give valuable insights to explain the complex dynamics of dune motion observed in this area by Le Bot and co-workers (2000, 2001, 2004) at short and long time scales.

Hydrodynamic Mathematical Modeling of the Yangshan Deep-Water Harbor Waters, China

Taking Yangshan sea-area of the Qiqu archipelago as an example, a 2D numerical model of tidal currents is established to study the change of the current field and the influence of branch blocking in different stages of northern port construction, including tide process, velocity and tidal prism, in the main channel waters and the branches. Verifications with the observed data indicate that the simulated results can reflect the current fields in the region. Based on the numerical model it is rechecked and researched the influence of branch blocking in different stages of northern port construction on the changing processes of hydrodynamic, including tide process, velocity and tidal prism, in the main channel waters and the branches. The paper is to provide the scientific basis for the construction of Yangshan Port’s subsequent engineering.

Study on hydrodynamic and sedimentation problems in development of harbors located at offshore area with many islands and tidal channels

The Yangshan sea area which locates in the Qiqu Archipelago is a typical offshore area with muti-island and muti-channel. In this paper, taking Yangshan sea-area of the Qiqu archipelago as an example, a 2D numerical model of tidal currents and sediments is established to study the change of the current and sediment field.The validity of the model is verified by the observation data obtained in April, 2007 including the tidal flow and suspended sediment concentration in the vicinity of the harbor. The verification of calculation shows the calculated values are in good agreement with the measured data. The field of tidal currents, suspended sediment concentration and the seabed deformation can be successfully simulated. Finally, two layouts are simulated to study the changes of the current and suspended sediment field. And the seabed evolution is predicted with the model. Computational results show that the Branch Channel Layout is advantageous to the present situation.

Numerical simulation of tidal current and erosion and sedimentation in the Yangshan deep-water harbor of Shanghai

Yangshan near-shore sea area is the multi-island and multi-channel area with strong flow velocity and high suspended sediment concentration. Based on the characteristics of tidal currents, waves, and sediment in the Yangshan area, a two-dimensional numerical model of tidal currents, sediment transport, and sea bed deformation is developed. In the model, the effects of tidal currents and wind waves on sediment transport are considered. According to characteristics of the study area, unstructured grids are applied to fit the boundaries of the near-shore sea area. The results show that the calculated values are in good agreement with the measured data. The field of tidal currents, suspended sediment concentrations, and the deformation of the seabed can be successfully simulated.

Numerical studies on ecological effects of artificial mixing of surface and bottom waters in density stratification in semi-enclosed bay and open sea

An apparatus, which mixes waters in upper and lower layers in density stratification and discharges the mixture at the middle depth, has made a remarkable success in enhancing water quality for ecosystems in a small semi-enclosed bay. In this study, we conducted numerical simulations by using a three-dimensional tidal current model and an ecosystem model to predict the effects of the apparatus in two different seas; a larger semi-enclosed bay and the area around a solitary island in the open sea. Isahaya Bay in Ariake Sea was chosen as the former case to see how effectively the apparatus can reduce oxygen-deficient water, and the sea around Okinotori-shima Island represents the latter, where we are interested in the effect of the apparatus on fertilisation; how much primary production can be increased. As a result, it is suggested that the apparatus reduced up to 70% of oxygen-deficient water in Isahaya Bay during the neap tide in high summer, although it is not very effective in fertilising around the solitary island; only 0.3% of chlorophyll-a was increased in the area affected by the apparatus.

Three-dimensional hydrostatic modeling of a bay coastal area

This article describes the development of a three-dimensional (3D) multilayer hydrostatic model of tidal motions in the Ariake Sea and its application. The governing equations were derived from 3D Navier-Stokes equations and were solved using the fractional step method, which combines the finite difference method in the horizontal plane and the finite element method in the vertical plane. This study introduced a 3D, time-dependent, hydrostatic, tidal current model that can compute wetting and drying in tidal flats due to tidal motion. The 3D model was first tested against analytical solutions for three standard cases in a rectangular basin in order to investigate the performance of the model. Then, the model was applied to Saigo fishery port and the Ariake Sea. For standard cases, the numerical solutions were almost identical to the analytical solutions. Finally, the model results for Saigo port and the Ariake Sea show good agreement with the field observations.

Hurricane Katrina Storm Surge Hindcast Using a Coupled Storm Surge, Wind Wave and Tidal Current Model on an Unstructured Grid

Hurricane Katina (2005) brought enormous damage to coastal protection systems in southern portions of the states of Louisiana and Mississippi, USA. In efforts to recover the devastated areas, construction of new systems to protect the areas from possible storm surge in the future has been a very urgent task. In this work, we develop a coupled storm surge, wind wave, riverine flow and tidal current model being used to design the new protection systems. The computational model employs the finite element method for the riverine, tide and storm surge model and takes advantage of unstructured grids to obtain precise estimation of possible surge heights from 100-year level storms. Observed hydrographs and high water marks during the hurricane are used to validate the developed model. The validation shows that the model is capable of reproducing the storm surge induced by the hurricane with good accuracy. The model is also found to be useful to understand how the hurricane caused the unprecedented surge levels.

Analysis of the Characteristics of Tidal Current at Kurushima Strait-Field Observations and Numerical Simulation of 3D-Flow

This study presents the results of analysis of the field observations and the numerical simulation of tidal currents in the Kurushima Strait. The field data measured tidal currents at the two points near the Strait for fifteen days and measured vertical distributions of tidal currents in the west channel of the Strait for 10 hours in one day. The numerical simulation is performed by a multi-level model of tide and tidal currents as horizontal eddy viscosity terms, described with the Smagorinsky's formulas, are incorporated. The specific peculiarities of the complex coastal line and bottom topography of the Strait are taken into account in the model. The tidal current fields are reproduced by the model. Several components of tidal currents and the location of streaks, generated in the Strait, can be predicted by the numerical simulation.

Numerical Modelling Studies To Predict ThePotential Impact On The Sediment Transport Of AProposed Outer Harbour At Great Yarmouth,UK.

An outer harbour is proposed to be constructed on the east coast of England at Great Yarmouth. As part of a series of studies during the planning stage HR Wallingford were commissioned to investigate the potential impact of the harbour on the adjacent sediment regime. A combination of models was used to simulate the sediment transport processes on the existing coast, and involved a comprehensive simulation of the littoral drift at strategic locations, and two-dimensional area modelling covering some 20km of the coastline and extending 10km offshore. A particular feature of this study was the requirement to simulate the effect of the complex and mobile offshore sand banks in modifying the propagation of waves from offshore to inshore and the associated effect on the littoral regime. A key aspect of any project of this scale is the need to verify relevant aspects of the model, in order that the greatest confidence can be given to the model's predictions. For this study information was gathered from a number of sources for use in verifying the wave propagation, tidal current, and littoral drift models. Simulation of the post-construction scenario highlighted the magnitude and extent of the potential impact of the harbour on the littoral drift, particularly with respect to the beaches immediately to the south. A series of sensitivity tests were performed to assess the natural variability in the littoral drift due to both the offshore wave climate and the configuration of the offshore sand banks. Maritime Engineering and Ports II, C.A. Brebbia & J. Olivella (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-829-5

Rapid water exchange between the lagoon and the open ocean at Majuro Atoll due to wind, waves, and tide

Current measurements and conductivity‐temperature‐depth surveys of the lagoon and ocean at Majuro Atoll, the Republic of the Marshall Islands, were made from January 10 to 24, 1997. A vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements by Fourier transform. A three‐dimensional, robust diagnostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles. We used the diagnostic model to examine the effects of wind stress, radiation stress, density gradients, and tidal stress on the exchange of water between the lagoon and the ocean. Wind effectively mixes the lagoon water in approximately 2 weeks. Tidal flushing appears to be restricted to a small area near the main channels connecting the lagoon to the ocean. Cross‐reef‐flat currents induced by radiation stress and flowing to the deep channels in the center of the northern boundary form the dominant mechanism for exchange between the lagoon and the open ocean, causing water to exchange completely with the ocean in about 15 days. Computer‐generated particles tracked through the lagoon showed that radiation stress is also the main forcing mechanism for particle export from the lagoon. However, the coupling of tidal exchange through the Calalin Channel and wind‐stress‐induced mixing in the lagoon could also provide a significant export mechanism, particularly for particles originating uniformly inside the lagoon.

Three-dimensional structure of tidal current in the East China Sea and the Yellow Sea

A three-dimensional tidal current model is developed and applied to the East China Sea (ECS), the Yellow Sea and the Bohai Sea. The model well reproduces the major four tides, namely M2, S2, K1 and O1 tides, and their currents. The horizontal distributions of the major four tidal currents are the same as those calculated by the horizontal two-dimensional models. With its high resolutions in the horizontal (12.5 km) and the vertical (20 layers), the model is used to investigate the vertical distributions of tidal current. Four vertical eddy viscosity models are used in the numerical experiments. As the tidal current becomes strong, its vertical shear becomes large and its vertical profile becomes sensitive to the vertical eddy viscosity. As a conclusion, the HU (a) model (Davieset al., 1997), which relates the vertical eddy viscosity to the water depth and depth mean velocity, gives the closest results to the observed data. The reproduction of the amphidromic point of M2 tide in Liaodong Bay is discussed and it is concluded that it depends on the bottom friction stress. The model reproduces a unique vertical profile of tidal current in the Yellow Sea, which is also found in the observed data. The reason for the reproduction of such a unique profile in the model is investigated.

A three-dimensional model of tidal currents in the mouth of the Tagus estuary

Three-dimensional simulations of barotropic tides are used to investigate the complex circulation at the mouth of the Tagus estuary. Comparison with field data shows that elevations are well represented in the main area of interest, but velocities are slightly over-predicted due to a simplified treatment of intertidal flats. Model results show the existence of strong velocity phase lags (up to 1.75 hours for the semi-diurnal constituents) between the shallow areas and the deep channel. These phase lags are partially responsible for the generation by advective accelerations of a strong residual velocity field (velocities reach 0.5 m s −1) with well defined eddies. The interaction between the residual and tidal velocity fields in turn generates strong chaotic stirring. Localized sigma coordinates (LSC), a recently proposed method which allows the number of nodes per vertical to vary horizontally, are used for the first time in a three-dimensional application. A previously proposed criterion for the horizontal distribution of the total number of vertical nodes is shown to be inadequate when advective accelerations are important. However, with an alternative criterion, the use of LSC reduces maximum errors by a factor of two relative to traditional sigma coordinates.

Numerical experiments of internal wave generation by strong tidal flow across a finite amplitude bank edge

Results of some idealized numerical experiments of strong tidal flow of a stratified fluid across a finite amplitude bank edge are presented. These experiments were motivated by a need to develop an understanding of some of the complex internal wave phenomena observed on Georges Bank (Loder et al., 1992) and at other locations where tidal forcing is strong. The numerical model solves the fully nonlinear, nonhydrostatic Boussinesq equations on an ƒ plane. The model is two‐dimensional, with spatial variation in the vertical and cross‐bank directions only. Model forcings are based on the Georges Bank observations. A horizontally uniform stratification is used. The model successfully reproduces some observed features including the formation of a large depression and a hydraulic jump over the bank edge during off‐bank flow and two on‐bank propagating depressions every tidal period. An undular bore propagating away from the bank is in agreement with other observations (La Violette et al., 1990). Rotational effects are shown to be responsible for the formation of the second of the on‐bank propagating depressions. Sensitivity of the results to the topographic slope, tidal current strength, stratification, and model initialization is explored.

Sensitivity analysis of a coastal marine ecosystem

An ecosystem with four compartments, i.e. PO4-P, phytoplankton, zooplankton and detritus, in a coastal region was considered. Sensitivity analysis of a phosphorus flow model in well-mixed water without currents concludes that (1) the maximal photosynthetic rate,V m , in Michaelis-Menten relation plays an important role in the distribution of biomass among compartments but the half saturation constant,K s , is not so important, (2) the natural death rate of phytoplankton is important for the ecosystem, (3) the natural death rate of zooplankton is also effective on the ecosystem. A numerical experiment was also performed on the ecosystem with four compartments are also studied using a dynamical barotropic model of tidal currents of Mikawa Bay (Japan). Diffusion coefficient in diffusion equation plays the role of a linear smoothing parameter in the horizontal distribution of compartment. On the other hand, perturbations of biological parameters cause nonlinear variations in the horizontal distribution of compartment.