A brief overview of plan-shape disequilibrium in embayed beaches: Tangier bay (Morocco)

Abstract

Embayed beaches commonly exhibit long-term equilibrium plan shape configurations that reflect either swash-alignment or drift-alignment (Davies, 1980) relative to the wave field, involving, respectively, virtually no longshore drift, and a balanced longshore drift over space and time. Within the context of an overall sediment budget in equilibrium, imbalances in longshore drift in embayed beaches are essentially generated by medium-term (order of several years) wave modifications in the incident wave field due to: (1) cyclic changes in deepwater wave approach directions caused by climatic oscillations; (2) human constructions, notably port breakwater structures. The latter type of engineered modification is perfectly exemplified by Tangier Bay. The beach in the eastern part of this bay has been steadily eroding over the past 50 years as a result of important port development in the western end of the bay that has perturbed waves from the Atlantic, generating, in particular, destabilization of a hitherto equilibrium drift-aligned system. The long-term resolution of problems generated by such perturbations requires a clear integrated management approach.