Long-Term Trends in Coastal Erosion and Accretion Along the Nigerian Atlantic Coast: Drivers and Projections

Nigeria's 853-kilometre Atlantic coastline exhibits a highly variable pattern of erosion and accretion driven by the complex interaction of wave forcing, longshore sediment transport, river discharge variability, sea level rise, and human modification of the coastal system. Despite the socioeconomic significance of this coast for the densely settled Southern Nigerian population, a rigorous long-term quantitative analysis of coastal change covering the full national coastline and resolving the relative contributions of natural and anthropogenic drivers has not previously been undertaken. This dissertation addresses this gap through analysis of a multi-decadal coastal change database constructed from historical topographic maps, aerial photography, and satellite imagery (Landsat 5/7/8/9, Sentinel-2) spanning 1972 to 2024, processed using the Digital Shoreline Analysis System and a novel automated waterline extraction algorithm validated against surveyed ground control points. Coastal change rates are computed for 17,000 shoreline transects at 50-metre spacing and classified by geomorphological setting (sandy barrier beach, estuarine delta, muddy tidal flat, rocky promontory). A multiple regression attribution analysis decomposes shoreline change variance into components attributable to wave climate trends (from ERA5 hindcast), sea level rise (from satellite altimetry), river discharge variability (from gauged river records), vegetation loss (from NDVI analysis), and human infrastructure (seawalls, groynes, beach nourishment, sand mining). Process-based XBeach-NH model simulations project coastal change under three sea level rise and storm wave scenarios to 2050 and 2100. The dissertation advances coastal change science by demonstrating that anthropogenic modification accounts for more than 50 percent of shoreline change variance in urbanised coastal sections. Keywords: coastal erosion, long-term shoreline change, Nigeria, sea level rise attribution, process-based modelling