1 a 3D Sediment Transport Model for Combined Wave-Current Flows (original) (raw)
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Intercomparison of sediment transport formulas in current and combined wave-current conditions
2009
The 2D horizontal morphodynamic modeling system MORSYS2D simulates bottom topography evolution in coastal zones. Sand fluxes are computed with different practical formulas, either for current dominated (e.g, Ackers & White, van Rijn) or combined wave-current flows (e.g., Soulsby van Rijn). Although sensitivity analyses of bottom topography changes in terms of the transport formulas used have already been done, a comparison of the sediment fluxes computed with the different formulations, considering the same flow conditions and using the parameterizations considered in the model (e.g, bottom roughness, bottom stress) is lacking. With that purpose, we have conceptualized a suitable range of wave and current conditions above a sand bed composed of uniform sediment that is characteristic of the conditions encountered in estuaries, tidal inlets and continental shelves, and applied the several flux formulations. To assess the differences obtained, the average value and the standard deviat...
3-D Numerical Modelling of Coastal Currents and Suspended Sediment Transport
Computational Science – ICCS 2006, 2006
A three dimensional hydrodynamic and suspended sediment transport model (HYDROTAM-3) has been developed and applied to Fethiye Bay. Model can simulate the transport processes due to tidal or nontidal forcing which may be barotropic or baroclinic. The Boussinesq approximation, i.e. the density differences are neglected unless the differences are multiplied by the gravity, is the only simplifying assumption in the model. The model is also capable of computing suspended sediment distributions, amount of eroded and deposited sediment. It is a composite finite difference, finite element model. At three Stations in the Bay, continuous measurements of velocity throughout the water depth and water level were taken for 27 days. Model predictions are in good agreement with the field data.
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To predict sediment transport in the coastal environment is of particularly importance for coastal and environmental engineers. The conventional 2DH computer models have certain limitation for their application in the complex flows. To describe details of flow structure across the water column and intra-wave processes, which are crucial for sand transport calculation, the present paper discussed implementation and validation of an intra-wave sand transport model with an existing phase resolving wave-current model. Model formulation and assumptions are presented briefly with details of model testing on several existing laboratory experiments. The model-data comparison indicates the ability of the numerical model system for sand transport prediction in a prototype scale. Further model validation and testing on field measurements are also needed.
Nowadays Problems of Sediment Transport Modeling in the Coastal Zone
Coastal Engineering Proceedings, 2014
The ultimate purpose of sediment transport studies is the prediction of bottom relief in the zone of active wave effect accompanied by transport of significant sand volumes. The energetic longshore currents induced by the oblique wave approach, transport large amounts of sand lifted by waves from the sea bottom. This mass sediment transport and its variations finally determine the shoreline configuration and the location of accumulative and erosion areas on the underwater slope. Because of great practical significance, the problem of sediment transport has attracted much attention. When constructing theoretical models of suspended sediment mass transport by water flows, investigators have to face a number of difficulties. Modeling of the sediment transport is limited by the absence of clear physical mechanisms of sediment suspension. The main difficulties of the modeling are discussed in this report.
Journal of Coastal Research, 2005
The sensitivity of estimated suspended sediment transport rates was studied by applying existing current-wave fields within a coupled numerical model using the Bagnold and the Soulsby-van Rijn formulae. The study area was the Sylt-Rømø bight, an enclosed back barrier tidal basin located in the North Sea. The bight has an area of some 400 km 2 in which sand flats prevail. This work provides numerical estimates of sediment transport rates and shear velocities throughout the Sylt-Rømø tidal basin. Water levels, vertically-averaged two-dimensional current velocities and wave spectra were used as input from validated numerical model calculations. Four days covering a full storm period in April 1997 were selected for the calculations of total bed shear velocities and sediment transport rates. The simulation shows that during moderate wave conditions sediment transport mainly takes place in the tidal channels. However, with high wave energy present, sediment transport becomes more important in shallow areas. The general distribution of shear velocities and suspended sediment concentrations over the basin suggests a large erosion and resuspension of sediment in shallow areas by wave action which may not be so evident in the sediment transport rates because of the low current velocities. This suggests that storms will continue to erode shallow areas, thus increasing the tidal prism and probably the tidal currents which will result in the continuing export of sediment.
A process-based model for sediment transport under various wave and current conditions
International Journal of Sediment Research, 2011
The purpose of this study is to investigate the capability of a newly developed process-based model for sediment transport under a wide variety of wave and current conditions. The model is based on the first-order boundary layer equation and the sediment advection-diffusion equation. In particular, a modified low Reynolds number k-model is coupled to provide the turbulence closure. Detailed model verifications have been performed by simulating a number of laboratory experiments, covering a considerable range of hydrodynamic conditions such as sinusoidal waves, asymmetric waves and wave-current interactions. The model provides satisfactory numerical results which agree well with the measured results, including the time-averaged/dependent sediment concentration profiles and sediment flux profiles, as well as the time series of concentration at given elevations. The observed influences of wave orbital velocity amplitude, wave period and sediment grain size are correctly reproduced, indicating that the fundamental physical mechanisms of those processes are properly represented in the model. It is revealed that the present model is capable of predicting sediment transport under a wide range of wave and current conditions, and can be used to further study the morphodynamic processes in real coastal regions.
Coastal Engineering, 1997
As a part of the MAST2 GS-M Coastal Morphodynamics project, the predictions of four sediment transport models have been compared with detailed laboratory data sets obtained in the bottom boundary layer beneath regular waves, asymmetrical waves, and regular waves superimposed co-linearly on a current. Each data set was obtained in plane bed, sheet flow, conditions and each of the four untuned numerical models has provided a one-dimensional vertical (lDVj, time-varying, representation of the various experimental situations. Comparisons have been made between the model predictions and measurements of both time-dependent sediment concentration, and also wave-averaged horizontal velocity and concentration. For the asymmetrical waves and for the combined wave-current flows, comparisons have been made with vertical profiles of the cycle-averaged sediment flux, and also with the vertically-integrated net sediment transport rate. Each of the turbulence diffusion models gives an accurate estimate of the net transport rate (invariably well within a factor of 2 of the measured value). In contrast, none of the models provides a good detailed description of the time-dependent suspended sediment concentration, due mainly to the inability of conventional turbulence diffusion schemes to represent the entrainment of sediment into suspension by convective events at flow reversal. However, in the cases considered here, this has not seriously affected the model predictions of the net sediment flux, due ' Corresponding author.
Three-Dimensional Modeling of Fine Sediment Transport by Waves and Currents in a Shallow Estuary
Journal of Geophysical Research: Oceans
A suspended sediment transport model is implemented in the unstructured-grid SUNTANS model and applied to study fine-grained sediment transport in South San Francisco Bay. The model enables calculation of suspension of bottom sediment based on combined forcing of tidal currents and wind waves. We show that accurate results can be obtained by employing two-size classes which are representative of microflocs and macroflocs in the Bay. A key finding of the paper is that the critical calibration parameter is the ratio of the erosion of the microflocs to macroflocs from the bed. Different values of this erosion ratio are needed on the shallow shoals and deeper channels because of the different nature of the sediment dynamics in these regions. Application of a spatially variable erosion ratio and critical shear stress for erosion is shown to accurately reproduce observed suspended sediment concentration at four-field sites located along a cross-channel transect. The results reveal a stark contrast between the behavior of the suspended sediment concentration on the shoals and in the deep channel. Waves are shown to resuspend sediments on the shoals, although tidal and wind-generated currents are needed to mix the thin wavedriven suspensions into the water column. The contribution to the suspended sediment concentration in the channel by transport from the shoals is similar in magnitude to that due to local resuspension. However, the local contribution is in phase with strong bottom currents which resuspend the sediments, while the contribution from the shoals peaks during low-water slack tide.
A unified sediment transport formulation for coastal inlet application
2007
The Coastal Inlets Research Program (CIRP) is developing predictive numerical models for simulating the waves, currents, sediment transport, and morphology change at and around coastal inlets. Water motion at a coastal inlet is a combination of quasi-steady currents such as river flow, tidal current, wind-generated current, and seiching, and of oscillatory flows generated by surface waves. Waves can also create quasisteady currents, and the waves can be breaking or non-breaking, greatly changing potential for sediment transport. These flows act in arbitrary combinations with different magnitudes and directions to mobilize and transport sediment. Reliable prediction of morphology change requires accurate predictive formulas for sediment transport rates that smoothly match in the various regimes of water motion. This report describes results of a research effort conducted to develop unified sediment transport rate predictive formulas for application in the coastal inlet environment. The formulas were calibrated with a wide range of available measurements compiled from the laboratory and field and then implemented in the CIRP's Coastal Modeling System.
Comparison of sediment transport formulae for the coastal environment
Coastal Engineering, 2003
Most existing sediment transport formulae to estimate transport rate in the coastal environment have a restricted range of applicability and are often used beyond this range. The aim of this paper is to investigate the limits of five of these formulae: the Bijker, Bailard, Van Rijn, Dibajnia and Watanabe, and Ribberink formulae. The sensitivity of these formulae to wave orbital velocity, wave period, wave asymmetry, sediment grain size, and steady current has been studied and tested against data for large velocities where significant errors can appear. The formulae behave in very different ways if one of the main parameters is slightly modified, particularly when fine sediments are present and phase-lag effect appears. But important discrepancies between formulae can also be observed for medium sand. At last, the wave-related sediment transport (due to wave asymmetry) has great importance for the morphodynamic and is only accounted for in the Bailard, Dibajnia and Watanabe, and Ribberink formulae. D