A modeling-based analysis of processes driving wave-dominated inlets

Among the different types of tidal inlets, wave-dominated inlets have been subjected to few quantitative studies, so that the physical processes controlling their dynamics are not fully understood. This study presents the application of a coastal area morphodynamic modeling system to a wave-dominated inlet (Óbidos Inlet, western coast of Portugal), in order to investigate the physical processes responsible for channel development during fair weather conditions and shoaling during periods of larger waves. The modeling system was able to reproduce reasonably well morphological changes at the Óbidos Inlet and subsequent tidal amplitude evolutions inside the lagoon over a period which includes 3 months of fair weather conditions, followed by 2 months representative of winter conditions. The inlet development during fair weather conditions was attributed to the strong ebb-dominance of the main channel without waves, enhanced by the combination of shallow channels and a meso-tidal range. The inlet infilling during the maritime winter was attributed to three main wave-induced mechanisms: (1) the onshore component of wave radiation stresse gradients, which is not fully compensated by the wave-induced setup in front of the inlet; (2) the acceleration and convergence of longshore transport toward the inlet, due to the presence of a strong lateral gradient in free surface elevation on both sides of the inlet, and, to a smaller extent, to wave refraction around the ebb-delta; and (3) the increase in mean water level inside the lagoon, which reduces tidal asymmetry and subsequent ebb-dominance.