Hydrogeomorphological dynamics and erosion of the soft coasts in tropical Africa, the case study of the Wouri estuary, Cameroon

Coastal erosion affects all countries along Africa's Atlantic coast, with flooding being the second most significant threat after erosion. In Cameroon, this phenomenon is particularly alarming, especially along the Kribian coast and in the Wouri estuary. Cape Cameroon in the Wouri estuary is experiencing severe erosion. The question arises whether the current erosion in the Wouri estuary is due to internal factors or part of a broader dynamic affecting all Atlantic African coasts. This inquiry aims to understand the causes of coastal erosion in the Wouri estuary. To address this, we used a large-scale map based on Landsat images (30m spatial resolution) covering the entire Wouri estuary and a smaller-scale map based on Pleiades images (0.5m spatial resolution) focusing on Cape Cameroon. The Digital Shoreline Analysis System (DSAS) in ArcGis 10.7.1 facilitated this analysis. Aerial photographs from 1916 to 2016 helped assess changes in Douala and their impact on mangroves over time. Diachronic land cover analysis employed Landsat images and the maximum likelihood algorithm. The Landsat results indicate that coastal erosion affects over 75% of the Wouri estuary's coastline, with average recession rates ranging from ± 3m to ± 11m between 1975 and 2020. Hotspots of regression include Cape Cameroon, the coastal spit around Manoka Island, and the area near the APD. High-resolution images from Pleiades and Google Earth confirm the severity of coastal erosion. The northern tip of Cape Cameroon is retreating at an estimated rate of + 15m/year, with the most significant recession measured at the tip of Cape Cameroon, estimated at 53 meters. A small accretion of + 5m is visible at Toubé, spanning no more than 100 meters.