Beach-dune degradation in a Mediterranean context of strong development pressures, and the missing integrated management perspective
The Mediterranean coast of Tetouan, south of the Spanish enclave of Ceuta, in Morroco, comprises headland-bound beach-dune systems bordering small coastal plains that are increasingly taken up by socio-economic activities and coastal infrastructure essentially related to tourism development. The 35 km shoreline shows a long-term (multi-decadal) erosional trend due jointly to the damming of the small wadis that hitherto supplied sand to the beach-dune system, the construction of leisure harbours that trap sand and act as boundaries to longshore sand redistribution, and continuous direct dune destruction. Over 95% of the coastal dunes on this microtidal coast have now been destroyed by housing and tourism infrastructure, in a national context marked by a total absence of beach-dune management, and inscribed in an antiquated coastal development setback line of only 3 m relative to the high water level. The short-term sediment budgets of two contrasting beach-dune systems were analysed on the basis of digital elevation models obtained from three successive surveys conducted in February and March 2008 in order to document coastal response patterns to storms under the present conditions of sediment budget stress. Ksar Rimal comprises a narrow beach and a virtually completely destroyed dune, and Cabo Negro exhibits a wider beach and a partially degraded dune. The two beach-dune sites showed balanced sediment budgets, and resilience following a succession of a severe storm (maximum significant wave height (Hs) offshore of 4.2 m), a moderate storm (maximum offshore Hs of 2.8 m) and fair-weather conditions (maximum offshore Hs < 1 m). The survey period is, however, too short to identify the imprint of chronic erosion, and at the short timescale of the study, the resilience shown by both beaches may simply imply that they are presently attuned to the current storm regime. Each beach exhibited a specific resilience mode. Ksar Rimal was dominated by changes essentially limited to the steep narrow beach, involving berm erosion and reformation. The mode on Cabo Negro beach involved sand exchange with the subsisting dune. Continuous dune destruction under development pressures and sand-supply deficit from the nearby wadis will, however, definitely be detrimental to both the protective role of dunes against storms and to beach-dune sand exchanges that contribute to the maintenance of a healthy coastal sediment budget. The case of the Tetouan coast is symptomatic of the situation of large portions of the coast of Morocco now under pressure from development, a situation that, unfortunately, mimicks that of many sectors of depositional coasts in the Mediterranean. Mitigation of coastal erosion requires a firm connection between coastal science and management, but also the rapid implementation of measures aimed at restoring the coastal sediment budget and assuring active beach-dune sand exchange.