Influence of river mouth sand spit level on the time variation of river stage and bed topography

Presence of sand spits at river mouths interrupt effluent flood flow into the sea. An appropriate flushing of the sand spit could reduce flooding intensity in the adjoining areas. Initial sand spit elevation influences initiation and development of flushing through a complex interaction of effluent flood discharge, tidal level and sediment transport processes. Present paper describes the influence of initial sand spit level on the time variation of river stage and corresponding development of bed topography under the actions of both tide and high flood flows. Model results show that initial sand spit level influences the magnitude of peak water level and its arrival time. The over-topping of sand spit and initiation of its flushing, however, show only little difference in time owing to very steep rise in effluent flood discharge. Sediment transport with low tide has been found to be higher than that with high tide as low tide forces lower water level at high discharges, therefore, causing high velocities. The sand spit has been seen to flush down into the sea forming a new channel section.