LARGE SCALE SHORELINE PROTECTION WITH MINIMIZED DOWNDRIFT IMPACT, COTONOU, WEST AFRICA

Abstract

Benin is a country in West Africa with a little more than 120 kilometers of coastline. The main port at Cotonou serving the country of Benin was completed in 1963. According to Dibajnia and Nairn (2004), Benin’s coastline experiences incessant wave attack causing a longshore sand transport rate in the order of 1 million m3 per year (moving from west to east). The port facility initially blocked the full amount of sand transported along the shore, resulting in accumulation of a large beach on the updrift (west) side of the port and corresponding dramatic erosion of the downdrift (east) shoreline consisting of over 400 m of shoreline retreat by 2003 (i.e. over approximately 40 years). Additionally, since 1998 sand started to bypass around the harbor breakwater into the entrance channel. Harbor entrance channel dredging requirements was escalating with almost 1.5 million m3 dredged between 1998 and 2002. At the time of port construction, the downdrift erosion was not a concern as the area was largely undeveloped. However, with the inevitable expansion of the city of Cotonou towards the east, the ongoing erosion started to destroy newly developed residential and commercial areas.