Sediment transport by waves and currents in the Pearl River estuary

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Sediment transport by waves and currents in the Pearl River estuary


Author: Chen, Yong
Title: Sediment transport by waves and currents in the Pearl River estuary
Degree: Ph.D.
Year: 2001
Subject: Sediment transport -- China -- Pearl River
Wave-motion, Theory of
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Structural Engineering
Pages: 1 v. (various pagings) : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: The dissertation describes a study of wave propagation, the interaction of waves and currents and the subsequent sediment transport through numerical methods. Two efficient numerical models have been developed for wave refraction and diffraction in large coastal areas with complex coastline configurations based on the wave action equation and the wave energy equation which take into account wave refraction-diffraction and the action of bottom dissipation. The wave action equation has been proved to be more suitable for large coastal area applications. Synchronous coupling of the wave propagation model based on the wave action equation with a 3D tidal hydrodynamic model is proposed for the study of wave and current interactions in larger coastal areas. The 3D hydrodynamic model is synchronously coupled with the wave model through a wave-current bottom boundary layer model and the vertical eddy viscosity coefficient. A fully 3-D numerical model for the simulation of sediment transport under the waves and currents for both non-cohesive and cohesive sediment has also been developed. An efficient operator splitting scheme is employed to solve the wave action conservation equation, the hydrodynamic momentum equations and the sediment transport mass balance equation in which the Eulerian-Lagrangian method is applied to the advective terms to increase numerical stability. The horizontal terms are discretized by an implicit finite element method and the vertical terms are approximated by an implicit finite difference method. A nominal-time iteration method is proposed to solve the non-linear irrotational wave number equation for wave directions. Laboratory data were selected to validate the numerical models. A number of tests on wave propagation, the interaction of waves and currents, and sediment transport under the interaction of waves and currents were carried out and the test results show that the present models are stable, accurate and efficient. The presented numerical models are verified against available measurements in the Pearl River estuary and good agreement has been obtained. In the western part of the estuary, the wave heights are reduced because of the bottom friction and shoaling effects. On the ebb, the opposing surface current can concentrate wave energy to cause a rapid and significant increase in steepness of sea surface. The total wave energy can easily increase by 50% from slack water to ebb. The bottom shear stresses are clearly larger when waves are present in addition to tidal currents, especially in the west shoal region. The largest bottom shear stress occurs in the east and west channels. The bottom shear stresses on the ebb are larger than those on the flood. Suspended sediment concentration significantly increases when waves are also considered. A sediment concentration of 100 mg/1 and 50 mg/1 may exist in the Lantau Channel and the north boundary, respectively. The sediment deposited in the west shoal during slack water is re-suspended by waves and currents and deposition and erosion occur at the upstream and downstream region of Qiao Island, respectively.

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