It is well known that estuarine systems are significantly affected by hydrodynamic conditions such as river discharge, storm surges, waves and tidal conditions. In addition to this, human interferences through developmental projects have the capability of disrupting the natural morphological processes occurring at estuaries. In West Africa, the goal to improve standards of living through large-scale dam construction, offshore ports and coastal erosion countermeasures has triggered alarming changes in the morphodynamics of estuarine systems. The estuaries at the Volta River mouth (Ghana) and “Bouche du Roi” inlet (Benin), located along the Bight of Benin coast, West Africa, were selected as two case study sites to examine their long-term morphodynamics and sandspit evolution. In this study, we primarily analyzed estuarine morphology using remotely sensed images acquired from 1984 to 2020. We further estimated the longshore sediment transport for this region using results from the image analysis and the depth of active sediment motion. Our results reveal that the longshore sediment transport rates for this region are in the magnitude of 10⁵–10⁶ m³/year. Comparative analysis with other estuaries and sandy coasts suggests that the longshore sediment transport along this coast has one of the largest rates estimated in the world.

This study assessed the deposition of sediment and shoreline evolution at two newly constructed port facilities in the Bight of Benin, West Africa. Based on the Building with Nature approach, the concept of a sandbar breakwater was implemented at the study sites. The coastal system of the bight is characterized by a sand barrier-lagoon system and a uniform prevailing wave climate, making it a favorable location for this innovative port solution. The case studies were undertaken at the Port of Lomé, Togo, and the Lekki Deep Sea Port (Dangote Sea Port), Nigeria, using remotely sensed shoreline positions and the one-line coastline change model for different periods. After construction of the breakwater, we estimated that the updrift coastline at the two locations accreted in the range of 10–23 m/year and the rates of sediment deposition were estimated to be in the magnitude of 1.0–7.0 × 10⁵ m³/year. The comparative study conducted also showed that these rates could further reach a magnitude of 10⁶ m³/year at other sediment-accreting landforms within the bight. We found that these large magnitudes of longshore sediment transport generated from very oblique incident waves (10°–20°) and sediment input from rivers (in orders of 10⁶ m³/year) have enabled the realization of expected morphodynamic changes on the updrift shoreline of the ports. From these results, downdrift morphological changes should not be underestimated due to potential imbalances induced in the sedimentary budget along the coastline. Future developmental plans within the bight should also continuously aim to adopt nature-based solutions to protect the ecosystem while mitigating unforeseen implications.

Coastal management around estuaries with highly morphological sandspits or barriers is one of the complex engineering tasks coastal researchers and engineers encounter. Insufficient studies or understanding of the morpho-dynamics of such areas results in poorly designed protection structures and hence exacerbating the existing problem being remedied. Therefore, this study aims at quantifying the sandspit growth and longshore sediment transport rates at the Bouche du Roi inlet in Benin, West Africa. The inlet has a constantly elongating updrift sandspit which results in narrowing and closure of the inlet. During rainy seasons, this poses flooding risks to surrounding communities. The study employed the use of remotely sensed images acquired from 1984 to 2020 to perform long-term analysis. Furthermore, the depth of closure and berm elevation for the study area were calculated using well known empirical formulas. Results from the sandspit analysis revealed an average updrift sandspit growth rate of about 700 m/year and an average longshore sediment transport rate of about 1.2 × 106 m3/year along the Bight of Benin. The results obtained from the method utilized in this study were similar to results from past studies in which different approaches were used.