Dramé, Awa Bousso; (2025) Coastal response to human interventions and climate variability: the Senegal estuary shoreline. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Coastal systems are at the forefront of the Anthropocene, undergoing transformations fuelled by increasing human pressure and climate variability. In West Africa, low-lying coasts host 56 % of GDP and 31 % of the urban population. Among them, Saint-Louis, a UNESCO World Heritage Site, is often portrayed as an amphibian city due to its location in the Senegal Estuary mouth, bound by the Langue de Barbarie spit. Although research has focused on the 2003 artificial breach, significant gaps remain in understanding the long-term evolution of this coast. My study bridges those gaps by integrating historical maps, satellite imagery, sediment samples, and statistics. Coupling geospatial analysis, machine learning, geochemistry, and environmental valuation, it investigates morphosedimentary environments and reconstructs human interventions over the past 300 years. It also examines wave climate variations linked to ocean indices (NAO, AMO, ENSO), shoreline changes since 1905 while assessing coastal vulnerability and the economic value of sand. Findings reveal that Saint-Louis population growth has driven coastal and water engineering developments since 1855 and polderisation operations in Sor (1905-1909). Furthermore, winter swells driven by negative NAO phases, and La Niña increases coastal sediment supply and cross-shore processes, generating erosion/accretion patterns. Areas south of Saint-Louis have been the most sensitive to natural breaching since 1854. Additionally, results demonstrate a 3-step response to breaching: massive erosion, adjustments/stabilization and progradation to its initial pre-breach position, expected by 2054. Consequently, 90% and 48 % of the Mauritanian and Senegalese coasts were moderately high and highly vulnerable in 2013-2023, with an average subsidence of -0.4 mm yr-1. Their translation into the economic valuation of sand evidenced the Mauritanian coast gained 2.68 x 106 m3 (±5,680 m3), worth 18,644,000 USD, whereas the Senegalese side lost 1.17 x 106 m3 (±9,200m3), equivalent to -8,115,000 USD. This study provides insights into integrated coastal management of cross-border coastal systems and supports sustainable sediment management plans.

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