Seasonal to decadal scale shoreline changes along the Cameroonian coastline, Bay of Bonny (1986 to 2020)

2021

Article référencé dans le Web of Science WOS:000670142200013

Njutapvoui F.N., Onguene R., Abessolo O.G., Rudant J.P., Bogning S., Stieglitz Thomas, Tomedi E.M.

Regional Studies in Marine Science, 2021, 45, 101798 [11 p.] ISSN 2352-4855

The Bay of Bonny, located along the Cameroon coastline, is home to diverse ecosystems. It is under significant pressure from large human activity, but remains very little studied, like much of the Gulf of Guinea. In order to understand its long-term shoreline variations and the role the wave regime plays in the evolution of the coastline, a study was conducted on the basis of optical image archives from Landsat and Sentinel-2A/2B satellite missions acquired between October 1986 and May 2020, coupled with daily ERA-Interim wave re-analysis data covering the period from January 1986 to August 2019. Overall, the results show that the evolution of the coast is highly variable in space and time, as indicated by different levels of erosion (30.55 %), and accretion (27.7 %) on the decadal-scale, with the most significant variations occurring in estuarine areas. Nevertheless, 41.75% of the Cameroon shoreline remains stable during the study period. Three main periods (1986-1994; 1995-2005; 2006-2020) during which the coast underwent significant changes a different location were identified, reaching a retreat rate of up to ?10 m/year in the northern section during the first period 1986-1994. The annual trend of significant wave heights anomaly along the coast (?5.6 to ?4.1 mm/year) with wave height maxima estimated at 1.46 ± 0.65 m, where observed during the summer months (July-August). Monthly shoreline changes are inversely correlated with wave climate in some segments. Eigenvalue orthogonal decomposition analyses (Mode 1, Empirical Orthogonal Function) show that 76.3% of the observed variability would be due to the relatively strong local influence of erosion and accretion. This local influence can be related to wave regime at shorter timescale (monthly to seasonal) and the sediment variability from the source inland to the coast at longer timescale (seasonal to decadal). These observations explain a complex pattern of shoreline changes with an almost continuous retreat shoreline during the period 1986-2013 and a reversal in trend towards accretion during the period 2013-2020. EOF mode 2 explains 23.7% of variability, which can be potentially associated with the synergetic relationship between tidal currents and wave-induced longshore current, tidal currents and possibly pockets of human activity. This is attributed to an overall decrease in the supply of sediment via the coastal transport system that prevails in the Gulf of Guinea.

Climatologie / Météorologie [032CLIMET] ; Sédimentologie [064SEDIM] ; Ecosystèmes [082ECOSYS]

Fonds IRD [F B010086267]

fdi:010086267