Refined flow modelling in coastal areas (original) (raw)

Tidal flow simulation in the English Channel and Southern North Sea

Advances in Water Resources, 1989

This paper presents the results of the II Tidal Flow Forum experiment of the English Channel and the southern North Sea. The model applies the FADI (falsified alternating direction implicit) scheme and uses the data base of the Tidal Flow Forum. Discrepancies between the model results and the distributed field data of 11 tide stations and 8 tidal current measurement points are shown graphically and are quantified by calculating the RMS (root mean square) errors and the standard deviations. Sensitivity tests have been carried out by changing some parameters (frictions, Coriolis .... ). The results which best fit the reference data were obtained by using the Manning's friction law. By doing so, the model can more appropriately adapt the complex bathymetry. The improvements are shown graphically.

Hydraulic modelling of tidal circulation and flushing in coastal basins

The Paper highlights the increasing concern of planners and designers for the hydroenvironmental problems relating to tidal circulation and flushing in small coastal basins, harbours, and marinas, and the use of physical and mathematical models as design tools to address such problems. Details are given of techniques frequently adopted in using both physical and mathematical models to quantify tidal flow patterns and water exchange characteristics of harbours and marinas. Emphasis is placed on comparative studies where alternative basin geometries and/or bathymetries are proposed. Advantages and disadvantages of both modelling techniques are considered. An example application of each approach is presented. The main purpose of the two studies was to investigate effects of basin geometries on the tidal flow and flushing features for two specific sites-one in the USA, the other in the UK. Results of both studies are reported, together with an interpretation of the data and a summary of the findings. Notatioo C , initial spatial average tracer concentration for volume considered C, spatial average tracer concentration for same volume after n tides E average per cycle exchange coeflicient n number of tides of simulation R average per cycle retention coeflicient T P R tidal prism ratio

Modelling of Flow in a Tidal Flat Area in the South-Eastern German Bight

This paper sums up the development phases of a flow model for a tidally-dominated area of the German North Sea. The study area is the Dithmarschen Bight located between the Elbe and Eider estuaries. The model presented is a two-dimensional depth-integrated flow model based on the DELFT3D Modelling System developed by Delft Hydraulics in the Netherlands. A description of model set-up as well as the results of sensitivity studies and model calibration and validation procedures are outlined in this contribution. Measurements of water levels and current velocities with a dense spatial and temporal coverage were used for this purpose. It was found that hydrodynamic forcing along the open sea boundaries is by far the most important factor governing the predictive capability of the model. Sensitivity studies indicated that the effect of seasonal bathymetric changes on current velocities may be quite significant. The effect of spatially variable bed roughness on the flow field was found to be less significant. The validation results showed that the model is capable of reproducing water levels and current velocities in the study area in fair agreement with observations. The mean absolute errors between computed and observed water levels at a number of locations covering periods of several months were found to be less than 10 cm (3 %of the mean tidal range) and 20 cm (6 %of the mean tidal range) at high and low water levels, respectively. The mean absolute errors between computed and observed depth-averaged velocities at various cross-sections in the tidal channels were generally found to be less than 0.2 m/s, which represents less than 20% of the tidally-averaged value. The model simulation results indicated a certain tendency towards underestimation of current velocities in the tidal channels. On the basis of the quality standards usually adopted (WALSTRA et al., 2001 and VAN RIJN et al., 2002), the performance of the model with regard to current velocity predictions was found to range between good and excellent.

Depth‐Averaged 2‐D Model of Tidal Flow in Estuaries

2004

A depth-averaged 2-D numerical model for unsteady tidal flow in estuaries is established using the finite volume method on non-staggered, curvilinear grid. The 2-D shallow water equations are solved by the SIMPLEC algorithm with the Rhie and Chow's momentum interpolation technique. The convection terms are discretized by one of the hybrid upwind/central difference scheme, exponential difference scheme, QUICK scheme and HLPA scheme. The algebraic equations are solved using the strongly implicit procedure (SIP). The model is capable of handling the drying and wetting problem due to the variation of water surface elevation. The model has been tested in Tokyo Bay and San Francisco Bay. The tests show that the present model is very stable and efficient. The simulated water elevation and flow velocity are in good agreement with the measured data.

Coastal Modeling System: Mathematical Formulations and Numerical Methods

2014

The Coastal Modeling System (CMS) is an integrated numerical modeling system for simulating nearshore waves, currents, water levels, salinity and sediment transport, and morphology change. The CMS was designed and developed for coastal inlets and navigation applications, including channel performance and sediment exchange between inlets and adjacent beaches. The present report provides an updated description of the mathematical formulations and numerical methods of hydrodynamic, salinity and sediment transport, and morphology change model CMS-Flow. The CMS-Flow uses the Finite Volume Method on Cartesian grids and has both fully explicit and fully implicit time-stepping schemes. A detailed description of the explicit time-stepping scheme was provided in Militello et al. and . The present report focuses on the recent changes in the mathematical formulations and the implicit time-stepping schemes. The CMS-Wave and CMS-Flow models are tightly coupled within a single inline code. The CMS-Wave and CMS-Flow grids may be the same or have different spatial extents and resolutions. The hydrodynamic model includes physical processes such as advection, turbulent mixing, combined wave-current bottom friction; wave mass flux; wind, atmospheric pressure, wave, river, and tidal forcing; Coriolis force; and the influence of coastal structures. The implicit hydrodynamic model is coupled to a nonequilibrium transport model of multiple-sized total-load sediments. The model includes physical processes such as hiding and exposure, bed sorting and gradation, bed slope effects, nonerodible surfaces, and avalanching.

A tidal simulation of Ariake Bay—A tideland model

Journal of Oceanography, 1994

A three-dimensional primitive ~r-coordinate model is developed to allow for tideland. The model determines the coastline position each time step based on a minimum threshold depth, and extrapolates the three-dimensional predictive variables onto tideland only when the water depth exceeds that threshold value, assuring that the extrapolation is consistent with physics as well as with the numerical scheme involved. The model is applied to an M2 tide in the northern estuary of Ariake Bay characterized by the large tideland. The model successfully simulates flood and ebb tides during which a large area of tideland is covered and uncovered with water due to the large tidal difference in sea level. The model also reproduces a strong salinity front caused by the freshwater runoff from Chikugo river. The general patterns of model-computed tidal flows and density front are consistent with data available in this region. The mean flow field averaged over a twelve hour period shows a strong northward current along the slope accompanied by anticyclonic eddies over tideland, the latter feeding a southward transport along the eastern coast. It is shown that such a circulation pattern is enhanced by the joint effect of baroclinicity and bottom relief. Finally, some implications of model results are discussed in relation to the fishery.

Modelling the three-dimensional tidal flow structure in semi-enclosed basins

2009

Coastal areas are generally intensely used areas with high population density and economic activity. On a basin scale the tide directly determines water levels and currents in a basin. These flow characteristics furthermore determine the shape of the basin itself, for example the forming and evolution of tidal sandbanks, which in turn influences the flow pattern. Because of its importance for various human and natural activities the modelling of tidal flow has been studied by many authors in the past. This has lead to depth-averaged (2DH) and 3D models amongst others The first analytical 3D-model that describes tidal flow in a semi-enclosed basin using Kelvin and Poincare modes with partial slip was created for this research. For this the method devised by Mofjeld (1980) for 3D tidal flow along a single coast with viscosity and no-slip was extended, thereby following Taylor’s approach (1921). As a reference situation the Northern Part of the North Sea was modeled and the properties ...

Numerical modeling of the tide in the coast ar-ea Casablanca-Mohammedia (Morocco)

International Journal of Advanced Geosciences

The objective of this study is to simulate the tidal circulation in the coastal area Casablanca-Mohammedia located on the Moroccan Atlantic. Simulations of the tidal currents of this zone use the 2D version of the MECCA (Model for Estuarine and Coastal Circulation Assessment). These simulations are based on the depth-integrated dynamical equations of turbulent motion. Equations are solved by using the implicit finite-differences techniques. The modelincorporates the actual bottom topography and the effects of the Earth rotation. As forcing mechanism, the model uses the tidal heights prescribed along the open boundaries.As first results, numerical experiments show that the model provides good results compared to those of the altymetric model TPXO.