Multi-decadal dynamics of the Saloum River delta mouth in climate change context

Abstract

The coast of Senegal is subject to climate variability that affects coastal dynamics. The Sangomar spit bounding the Saloum River delta provides a striking example. The spit dynamics has been characterized by complex changes involving both erosion and accumulation. Using a methodological approach combining remote sensing and data analysis in a Geographic Information System (GIS) we calculated a mean annual erosion rate of −3.55 m of the spit shoreline from 1954 to 1987. In 1987 the spit was breached by storm in its most eroded sector (- 4.59 m/year). This breach widened significantly to attain 5.25 km in 2018 and has now become the Saloum River mouth. The breach has resulted in exacerbated erosion of adjacent shorelines, especially at the down-drift coast, where the retreat attains a peak of −20.16 m/year, the average erosion rate remaining at −3.56 m/year for the entire coast. Extension of the spit tip has favoured progradation of the Sangomar Pointe which has lengthened by 5.74 km between 1954 and 2018, diverting gradually the Saloum River former mouth towards the South, and corresponding to a 5,185,009 m3 sedimentation. Extrapolation of shoreline mobility reveals high erosion rates due to sea-level rise by 2050 and 2100.