Saint Louis, Senegal. West Africa crystalizes most of coastal environmental and societal issues and subsequent vulnerability. Saint Louis is a historical city (World Heritage) located in the National Park of the Langue de Barbarie, a 10-km long sandspit at the mouth of Senegal river. From its situation, it is vulnerable (erosion, flooding) to both hydrologic and oceanic variability. This intermediate barred micro-tidal beach is located in the intertropical storm-free environment, with long energetic waves coming from high latitudes with an oblique angle, driving a strong longshore drift. As part of the COASTVAR project, an international intensive field experiment was conducted at Saint Louis from Dec 4th to 13th 2016 to quantify the natural role of protection played by the sandbar, longshore current, and transient exchanges with the inner shelf. (Photograph taken by Rafael Almar, LEGOS.)