Morphological Characterization and Evolution of Tahadart Littoral Spit, Atlantic Coast of Morocco

Abstract

Tahadart littoral spit on the Atlantic coast of Morocco is a mesotidal environment composed of 6 km long sand spit with flat and wide beaches, foredunes and vegetated dune ridges and well developed salt marshes. Tahadart’s littoral zone is affected by east and west winds and is exposed to waves approaching from the NE with an associated SW-directed littoral drift. Detailed 3D surveys reveal the spit as a flat, dissipative beach with small changes that take place homogeneously along the foreshore according to the parallel retreat model. Such a dissipative morphodynamic state was confirmed by means of classical parameters such as the Surf Scaling, Surf Similarity and the Dean number. The littoral evolution of the area was determined through analysis of the position of the dune foot evolution in 1981 and 1997 aerial photographs as well as the 2007 SPOT image by means of GIS tools. Coastal evolution was revealed by examining changes between the earliest (1981) and the latest (2007) shoreline positions. Accretion clearly prevailed over erosion and was particularly so in the northern part of the littoral (95 m, 3.7 m/year), at the river mouth (90 m, 3.5 m/year) and at southern part (the free edge) of the sand spit, with seaward and southward displacement of shoreline values increasing from north (12 m) to south (c. 180 m, 6.7 m/year). Behaviour observed at the free spit’s edge matched well a model of continued beach growth/progradation and allowed three different areas with specific beach growth mechanisms and rates to be determined.