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A 2D River morphology model with a curvilinear grid is developed to simulate the flushing river mouth bar occurred at the Ara River in July 2004. In the hydrodynamic model, the 2D free surface flow is calculated by the Saint Venant equations which are solved by an implicit finite difference technique and the ADI method. In the morphological model, the Van Rijin's model is used to evaluate sediment transport including bed load and suspended load. The helical flow and the transverse bed slope modify the bed load sediment transport. The bed level change is computed by a sediment continuity equation of the bank erosion model. The model is validated by comparison with the observations of water level variations and the riverbed topography at the mouth. A factor analysis is conducted to evaluate the effects of discharge, tide level, and grain size. The result shows that differences of sea elevation and peak discharge have significant effects on a process of morphological change at the river mouth.

Male' Island, the capital of Maldives, was hit by Indian Ocean Tsunami on December 26 2004, but the damage was less severe in comparison with other islands in Maldives and neighbor countries. One of the major reasons was attributed to the solid seawalls surrounding the island. In this study, the effects of the seawalls were inspected by numerical simulation, in which the finest grid size was 3.33m for the whole Male' Island. The results indicated that Male' Island without seawalls would have been hit by run-up flows with higher energy several times, especially on the east coast facing to the tsunami source. Thus it is certain that the existing seawalls reduced the damage of Male' Island as long as this event. In fact, the maximum tsunami height in Maldives, however, was relatively small, approx. 2m, so that the existing seawalls worked well against the tsunami. So it may be needed to implement other software methods; forecast and alert system, evacuation guideline system etc., as well as shore protection structures in preparation for larger scale tsunamis.