Seasonal shoreline behaviours along the arcuate Niger Delta coast: Complex interaction between fluvial and marine processes

Deltaic coasts are dynamic geomorphic systems where continuous changes occur on diverse spatial and temporal scales, and these changes constitute an important aspect of their evolution. Based on three-year satellite-derived shoreline data coupled with re-analyzed wave data and hydro-meteorological data, a comprehensive analysis of the dominant processes governing the seasonal shoreline changes along the oil-rich arcuate section of the Niger Delta, in the Nigerian Shelf of the North Atlantic Ocean has been undertaken. Shoreline analysis results show that the delta coast is characterized by predominant summer erosion and maximum winter accretion. Between 2010 and 2012, erosion dominated over accretion and a total of 9.1 km2 deltaic land was lost to coastline erosion at an annual average erosion rate of 4.55±1.21 km2/yr. A greater understanding of the dominant factors responsible for the change is presented. Shoreline change interactions with cross-shore sediment exchange processes are prominent at seasonal timescale (Summer R2=−0.85 and Winter R2=0.7), and interannual timescale (R2=−0.93) with longshore sediment transport processes. Correlation analysis reveals a gradual degeneration of relationship between the suspended sediment flux and coastal hydrodynamics beginning from 2010 to 2012 (cross-shore transport, R=0.68, 0.36 and 0.2 for 2010, 2011 and 2012, respectively; longshore transport R=0.63, 0.44 and 0.2 for 2010, 2011 and 2012, respectively). The study concludes that the effect of fluvial sediment reduction to the delta coast due to capital dredging of the Lower Niger River channels between 2009 and 2012, and periodic fluctuations in the nearshore hydrodynamics processes caused the observed annual shoreline erosion that eventually forced the deltaic coastline toward a state of landward migration during the study period.