A morphodynamic model to simulate the seasonal closure of tidal inlets

Seasonally open tidal inlets usually occur in microtidal, wave-dominated coastal environments where strong seasonal variations of streamflow and wave climate are experienced. These inlets are closed to the ocean for a number of months every year due to the formation of sand bars across their entrances. The annual closure of these inlets inhibits ocean access for boats and could also cause deterioration of water quality in the estuary/lagoon connected to the inlet. As these estuaries/lagoons are commonly used as harbours or recreational facilities there is increased interest in keeping the inlets permanently open. A process-based numerical model capable of simulating inlet closure is invaluable in terms of identifying the natural processes governing inlet closure. As a further step, this type of model could also be used to determine the effect of any proposed engineering solutions to keep the inlet open on the adjacent beaches. A morphodynamic model capable of simulating the seasonal closure of inlets, which includes both longshore (LST) and cross-shore transport (CST) processes, was developed in this study. Application of the model to two idealised scenarios indicated that cross-shore processes govern inlet behaviour when LST rates were low. The Dean's criterion [Dean, R.G., 1973. Heuristic models of sand transport in the surf zone. Proc. Conf. on Eng. Dynamics in the Surf Zone, Sydney, pp. 208-214.] for on-offshore transport was employed to show that, for small offshore wave incidence angles, onshore transport aided inlet closure when the offshore wave steepness (H-o/L-o) was less than the critical wave steepness (H-o/L-o)(crit), while offshore transport helped to keep the inlet open when (H-o/L-o) was greater than (H-o/L-o)(crit) LST was found to be the dominant process leading to inlet closure when (H-o/L-o) was much larger than (H-o/L-o)(crit) or when the offshore wave incidence angle was large. (C) 1999 Elsevier Science B.V. All rights reserved.