Analyzing time evolution of a tidal inlet due to nonlinear tides, sea level rise and waves with an idealised model

Abstract

A tidal inlet is a connection between the ocean and a basin behind the shoreline, in which water motion is dominated by tides. Such basins evolve over time due to asymmetries in tidal currents, waves and sea level rise. The primary objective of this research was to establish the presence of stable morphodynamic equilibria for tidal inlet systems. Other goals were finding the dominant hydrodynamic processes governing net sand transport and studying the response of the basin to sea level rise and waves. This has been done by calculating approximate solutions to one-dimensional nonlinear shallow water equations, and coupling them to simplified expressions for sand transport, as well as for evolution of length and depth. It is found that tidal currents can create stable equilibria, but not for basins with dimensions that resemble those on the Holland coast, with lengths less than 100 km. In particular, it is found that for smaller sized basins, infilling by the tidal current alone is too weak to compensate for the creation of accommodation space by current-day sea level rise. The simulations are in line with research on the Holocene evolution of the Holland coast. The Wadden Sea has not closed during this time, since the transport due to tides and waves was sufficient to compete with sea level rise. However, with projections of higher sea level rise in the near future, the Wadden Sea is at risk of drowning.