The filling dynamics of an estuary: from the process to the modelling (original) (raw)
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Numerical modeling of cohesive sediment transport and bed morphology in estuaries
2005
The present dissertation is the result of a research effort carried out in Laboratoire d'Ingénierie Numérique (LIN) of the School of Engineering (STI) in the Institute of Energy (IE) at the Swiss Federal Institute of Technology, Lausanne (EPFL). I wish to express my heartleft thanks to Professor Michel O. Deville, Mustafa S. Altinakar and Alfio Quarteroni, for offering the chance to study simultaneously in LIN, LHE (Laboratoire d'Hydraulique Environnementale) at EPFL, and to interact with the MOX (Laboratorio di Modellistica e Calcolo Scientifico) at the Politecnico Milano in Italy. They provided me with a pleasant research environment, many discussions and continuous encouragement. Prof. Michel O. Deville gave me the opportunity to come to EPFL within the LIN (former LMF) and he has always been confident in me, and I am very appreciative of his continuous support and guidance. This was the start of a very productive scientific interaction and the opening of a wonderful period in my life. I am grateful to Prof. Walter H. Graf with special thanks to Prof. Mustafa S. Altinakar, who gave me their intelligent guidance. From the beginning of my thesis they interested me in research on environmental, river and lake hydraulics, during many fruitful discussions we have had. I am specially indebted to Dr. Edie Miglio with whom I have learned a lot, not only about numerics. He gave me invaluable help for my research and helped me without reservation during my numerous visits to Milano. Special thanks to Prof. Alfio Quarteroni and Prof. Fausto Saleri who gave me many fruitful assistances and to have provided me with an essential part of data for the Po River Estuary. I would like to express my gratitude to the members of the jury, Prof. M. O. Deville, Prof. M S. Altinakar (NCCHE-Mississipi), Prof. A. Quarteroni (EPFL), Dr. J. Bühler (ETHZ), Dr. E. Miglio (MOX-Politecnico Milano) and the president of the jury Prof. C. Ancey (EPFL) for accepting to read my thesis and to be part of the jury. I am also indebted to Professor Ebenezer Njeugna, for his support at the beginning of my research and especially to have been the first to interest me in the study of the hydro-sedimentary flows within estuaries. He enabled me to carry out a practical training course with the port of Douala located on the Wouri Estuary in Cameroon. Thanks to the General Manager of the "Port Autonome de Douala-PAD" and to all his/her collaborators of the division for the maritime field for their perfect collaboration. Special thanks to Dr. Koen Blanckaert who provided me with some useful benchmark data and helpful advice during my research. Many thanks to Mrs. Cathérine Vickenbosch and Annette Jaccard of the Service of orientation and council, mobility, social service at EPFL, for their support at the time of my arrival in Switzerland. Many thanks to Mrs Birgitta Mergozzi (our secretary), Dr.
Modelling cohesive sediment transport in estuarial waters
Applied Mathematical Modelling, 1986
Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depth-averaged, finite element (FE) cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the frequency and quantity of dredging required to maintain navigable depths and the fate of adsorbed pollutants. Algorithms which describe the processes of erosion, dispersive transport, deposition, bed formation and bed consolidation are incorporated in CSTM-H. The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Partial verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. Model applications under prototype conditions are described.
Hydrodynamic and sediment suspension modelling in estuarine systems
Journal of Marine Systems, 1999
A fully-3D finite difference baroclinic model system for hydrodynamics and fine suspended sediment transport is described. The hydrodynamic model is based on the hydrostatic and Boussinesq approximations, and uses a vertical double sigma co-ordinate with a staggered grid and a semi-implicit two-time level scheme. In addition to the momentum and continuity equations, the model solves two transport equations for salt and temperature and an equation of state to include the baroclinic effects. The simulation of cohesive sediment transport processes is performed solving the 3D-conservative advection-diffusion equation, in the same grid used by the hydrodynamic model. Flocculation, erosion and deposition of sediments on the bottom are represented by means of empirical formulations parameterized by field data. The models were Ž tested and calibrated by simulating tidal flows and suspended sediment transport in several estuaries two applications are . described in Part II . The results show good agreement between the numerical predictions and the corresponding field measurements. q montmorillonite and kaolinite-organic matter and a small percentage of sand and silt.
Modeling Estuarial Cohesive Sediment Transport
Coastal Engineering Proceedings, 1984
Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depth averaged, finite element cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the fate of sorbed pollutants and the frequency and quantity of dredging required to maintain navigable depths. Algorithms which describe the transport processes of redispersion, resuspenslon, dispersive transport, settling, deposition, bed formation and bed consolidation are incorporated in CSTM-H. The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. A model application under prototype conditions is...
International Journal of Sediment Research, 2020
In order to optimize ship navigation in the macrotidal Gironde Estuary, a recent project funded by the port of Bordeaux aims at better understand and forecast hydrodynamic and fine sediment transport within the estuary. In the framework of this project, a twodimensional hydro-sedimentary model is built. The model includes hydrodynamic forcings, mixed-sediment transport, and consolidation processes. The harmonic analysis of the astronomical tides reveals a strong distortion of the tidal wave inducing the growth of overtide constituents and the non-significant effect of tide-surge interactions in annual-scale prediction. Depending on hydrological conditions, river discharge can considerably alter the model accuracy due to the migration of the turbidity maximum zone modifying the bottom roughness. Comparison with measurements shows the ability of the model to reproduce suspended-sediment concentrations in the central Estuary. Sensitivity of the model to sediment features has also been discussed in regard of suspended-sediment concentrations and fluid mud deposits. The model will be further coupled with ship squat and morphodynamic models. p { margin-bottom: 0.25 cm; line-height: 115%; }
Modelling of cohesive sediment transport in a tidal lagoon—an annual budget
Marine Geology, 2005
The annual net sediment flux for an enclosed estuary is usually calculated as a residual value in sediment budget studies based mainly on sediment core dating. In this study, the numerical model MIKE 21 MT was used to directly model the annual net transport of cohesive sediment for the Lister Dyb tidal area in the northern part of the European Wadden Sea. The model was calibrated by use of a combination of field data and calibration parameters derived from existing literature. The model reproduced the hydrodynamics satisfactorily as well as the concentration level and variation of suspended cohesive sediment concentration. Net import for the year 2002 was found to be 45 000 t of cohesive sediment, corresponding to a mean tidal period import of 64 t which compares to an approximate deposition of 0.1 mg l À1 of the tidal prism. Gross annual transport through a control cross section of the tidal inlet was 1 million ton meaning that 4-5% of the sediment transported in suspension was on average deposited within the tidal lagoon. This net transport was found to be rather constant from tidal period to tidal period thus supporting the theory that the processes of settling and scour lag, tidal velocity asymmetry together with sediment floc formation are the controlling processes for import of fine-grained sediment to shallow coastal plain estuaries. Temporary export of sediment from the area occurred during two major wind events in January and February when the maximum loss of sediment during one single tidal period was computed to be 40 000 t which is of the same order as the yearly net import of sediment. This indicates that net annual import of cohesive sediment to shallow estuaries may be much more variable than inferred from core dating studies found in literature. D
The effect of the joint action of M 2 and M 4 tidal flow, residual flow and spatial settling lag on the lateral entrapment of sediment is examined in tidally dominated estuaries with an idealized model that assumes along-estuary uniform conditions. Approximate solutions are obtained for arbitrary cross-channel bed profiles by scaling and perturbation analysis. The hydrodynamics include externally driven M 2 tidal flow, externally and internally driven M 4 tidal flow and residual flow driven by horizontal density gradient, river discharge and nonlinear advection. The sediment concentration includes a mean component, an M 2 component driven by bed erosion and an M 2 component driven by both bed erosion and inertial terms. Sediment availability is calculated by imposing a morphodynamic equilibrium condition. The model is applied to a transect in the James River estuary where data of flow and suspended sediment concentration are available. Two types of sediment are separately considered, viz., fine silt and coarse silt. Residual advective transport of sediment by the lateral flow induces trapping of sediment over the left shoal (looking landward). Model results also show that the incorporation of M 4 tidal flow and spatial settling lag leads to a second sediment trapping region over the right shoal. Model results are qualitatively in good agreement with the observations. , , thus . The superscript * indicates the conjugate part of a complex variable.
6 The Filling Dynamics of an Estuary: From the Process to the Modelling
2013
Estuaries are submitted to a natural filling caused by the settling of cohesive sediments ( � < 63 µm). Those sediments, coming mostly from the sea, are transported in estuaries by the tidal currents during ebb and flood flows. During slack water, fluid velocities vanish and particles are no more suspended by turbulent dispersion. Sediment particles settle towards
Modelling hydrodynamics and sediment flux within a macrotidal estuary: problems and solutions
The Science of The Total Environment, 2003
A model of estuarine circulation and sediment transport is described. The model uses a 2-D longitudinal and vertical grid to predict the distribution of tidal elevation, current velocity, density and sediment concentration. It has been developed for relatively narrow estuaries that have a large tidal range and potentially high river flow. The advantage over simple 1-D and depth-averaging 2-D models is that it can give reasonable representation of both gravitational circulation and the vertical distribution of suspended sediment concentrations, thereby providing better estimates of the bottom stress and sediment flux, particularly in the deep channel. The model has been developed as a management tool to provide some of the advantages of a full 3-D model, but with smaller development and running costs. It can be used to predict concentrations of contaminants in estuaries that have a significant load of suspended cohesive sediment, and can differentiate between dissolved contaminants and those that are attached to suspended sediments. It is a potentially useful tool for predicting the distribution of relatively short-lived contaminants that are affected by sediment concentration, such as bacteria and some radionuclides. ᮊ