Numerical Modelling of Geomorphological Processes in Estuarine Waters

Long Term Numerical Modelling of Geomorplogical Processes in Coastal and Estuarine Waters, with Particular Emphasis on the Unsteady Initiation of Motion for Sediment Particles

Abstract

Numerical modelling of geomorphological processes in rivers, estuaries, harbours and coastal waters is an efficient means of predicting bed level changes for further use in planning the maintenance and management of these areas. Nowadays, quasi-3D models are increasingly popular, particularly with the rapid progress in the power of modem day computers. In this thesis the development and application of two-dimensional and three-dimensional numerical models for predicting geomorphological processes in estuarine waters have been under consideration, with particular emphasis on the unsteady initiation of motion criteria for sediment particles. The governing hydrodynamic, sediment transport and bed level change equations are reviewed in their differential form by using the conservation laws of mass and momentum for fluid and sediment particles. Then the depth integrated and layer integrated form of these equations are derived for the domain. Different solution procedures for developing the geomorphological model are discussed in this thesis according to the nature of flow for different computational domains. A new unsteady criteria for the initiation of motion has been proposed based on the mathematical analysis of the physical processes. In this hypothesis, it is assumed that tides can be approximated by a sinusoidal wave and by applying Newton's second law then the resulting time varying forces acting on sediment particle can be calculated. The proposed criteria for the initiation of motion have been included in the geomorphological models, namely GEO-DIV AST and GEO-TRIV AST, which have been developed for two-dimensional and three-dimensional geomorphological simulations based on depth integrated and layer integrated algorithms respectively. A series of experimental tests have been undertaken in a laboratory rectangular harbour to verify the geomorphological model. The measured bed level changes for the various values of related parameters are presented for the verification and validation of numerical models and proposed criteria. The numerical models have been run for several case studies including: (1) migration in a trench, (2) bed level changes in a partially closed channel, (3) geomorphological development in the laboratory rectangular harbour, and (4) geomorphological developments in the Humber Estuary due to tidal currents. Predicted velocity, sediment concentration distributions and bed level changes have been illustrated to show the geomorphological developments in the corresponding computational domain. The predicted velocity, sediment transport and bed level changes have been compared with measured laboratory and field data and also numerical results of reported models in the literature, with an encouraging degree of similarity being observed for all cases, confirming the validation of the proposed new criteria for the initiation of motion and the GEO-TRIV AST numerical model for successful three dimensional estuarine flow simulations.

URI

https://bradscholars.brad.ac.uk/handle/10454/20905

Type

Thesis

Qualification name

PhD