A dissertation submitted in partial fulfillment for the requirements of the degree of Doctor of Engineering, School of Engineering and Technology

Thesis (Ph.D.) - Asian Institute of Technology, 1997

Prediction of sediment transport and morphological changes, deposition and erosion, is very vital in estuary projects, such as development and management of navigation, ports and harbours, environment management, etc. For long-term computations (monthly, seasonally, annual and longer), integration procedures of short-term simulation results over tide and wave climate are developed , however these techniques still contain a great deal of arbitrariness and are not systematically verified so far. This study is aimed to formulate a reliable and effective computation procedure to predict morphological change of estuaries. A two-dimensional depth-averaged morphological model is developed and used for all simulations. The model consists of 4 decoupling components: depth-averaged hydrodynamic model, RCPWAVE model, depth-averaged sediment transport and bed evolution models. It is formulated for well-mixed estuaries with wave and tide coexistence where tide is dominant, mixed sediment (sand and mud) and mixed mode sediment transports. The change of seabed is not updated into the tidal flow and sediment transport computations, the model is therefore classified as an initial model. From analysis of numerical simulations, spring tide is specified as the morphologically representative tide of the fortnightly neap-spring cycle. It is then proposed that the fortnightly siltation volume is computed from the spring-tide volume with the use of a multiplication factor M. Action of the wave climate is incorporated into the spring-tide siltation volume, which is taken as the weighting average over all representative wave conditions of the wave climate. Wave climate is proposed to be represented as a set of most important wave heights and periods coming from the monthly mean direction. The proposed values of multiplication factor M and wave representation have been verified satisfactorily. The proposed procedure for monthly computation serves as a tool to specify the distribution pattern and to quantify the amounts of sediment deposition and erosion over a seabed area. It is verified to work well for all time periods of the year in either wet or dry seasons, monsoon seasons or transitional periods. Computation works have been reduced significantly with the proposed integration over tide and wave.