Assessment of soft coastal protection alternatives for Saint-Louis (Senegal)

Abstract

The Barbarie spit (Langue de Barbarie) is a 100–400 m-wide West-Africa coastal barrier that has fluctuated in length between 10 and 30 km over the last century (Anthony, 2015). The changes in length reflect the variable position of the Senegal river mouth, where rates of spit growth vary greatly (100 to 700 m/year), depending on variations in wave characteristics, river discharge and river mouth dynamics, combined with barrier-breaching events (Bergsma et al., 2020). The Barbarie sandy barrier protects the island of Saint-Louis, within the Senegal river delta. Of particular significance is the historic city of Saint-Louis, a UNESCO world heritage city (Anthony, 2015). Coastal erosion can be severe along the 2 km stretch in front of Saint-Louis, with retreat rates of up to 20 m/year (Tavenau et al., 2021). Moreover, the coast in front of the city is home to small-craft fishing activity of high socio-economic implications. Given the Saint-Louis settings and the Barbarie spit dynamics, the city is at high coastal erosion and flooding risk. So, informed coastal management is necessary, based on the assessment of alternative coastal protection solutions. Given the world-wide success of several soft-management (beach nourishment) interventions, this paper addresses and compares four alternative solutions, consisting of artificial protective offshore islands and shore-attached peninsulas.