Salinity intrusion and dispersion modelling in a Malaysian estuary

The flow structures in rivers with floodplains vegetated with mangrove swamps were investigated in this thesis. Two natural estuaries namely Sedeli Estuary and Rompin Estuary were used in this study. Both estuaries are situated in the western coast of Malaysia and are about 100km apart. Field data were collected at both estuaries to compare their characteristics. Water levels, salinity reading and tide levels during high water were recorded for three days. They were used to calibrate the numerical mode ling results. Six different estuary layouts were used in this study. TELEMAC 2D was used to predict the velocity, water levels and salinity distribution at the apex and straight sections of compound meandering channels. The aim was to investigate how the shape factor, the presence of vegetated and non-vegetated floodplains and estuary configuration affected the velocity distributions, water levels and salinity distribution. Single and multiple Manning's were used to study the effects of Manning's on the results. Two mesh densities and three turbulence models were used in the simulation works for calibration and sensitivity analysis. Twenty simulation runs were done in this thesis to also study the effects of mesh independency and the choice of Manning's values on the results obtained. The results show that the vegetated floodplains are significant to the flow in the main channel. It was found that the flow at the apex and straight sections of the meandering channel showed some complexity due to the presence of vegetated floodplains, the tidal influence as well as the change of the inflow of freshwater into the system. The tidal flow within mangrove areas depend a large degree upon the submerged vegetation density with the tidal stage. In general, the results show that the choice of Manning's for floodplains, the main channel, and the estuary layouts will induce energy losses due to momentum the exchange between the main channel and floodplains.