Non-linear response of shoreface-connected sand ridges to interventions

Abstract

A non-linear morphodynamic model of a microtidal coastal shelf is used to study the response of shoreface-connected sand ridges and the net sand balance of the shelf to large-scale interventions. The model describes the interaction between storm-driven currents and the erodible bottom. The transport of sediment comprises both bedload and suspended load contributions and is due to the joint action of waves (stirring of sediment from the bed) and net currents (causing transport). Three basic types of interventions are studied: extracting sand from ridges, nourishing sand at the shelf and constructing navigation channels.  The model results indicate that for all interventions studied a relatively fast local recovery (time scale of decades to centuries) of the disturbed bathymetry to its original pattern takes place. Readjustment of the global system to its original equilibrium state (the saturation process) occurs on a longer time scale (several centuries). During the adjustment stage, significant net sand exchanges between inner shelf and adjacent outer shelf and near-shore zone occur. The results further suggest that extraction of sand from the shelf and dredging of navigation channels have negative implications for the stability of the beach (its sand volume decreases).