Influence of Amenities in the Functioning of a Coastal Sediment Cell with a Moving Barrier: Case of Benin Coastal Segment between Hillacondji and Djondji in the Township of Grand Popo

The coast of Benin, 125 km long, is partof the overall west African coast, characterized by a narrow strip of coarse and medium sand and by an important coastal transit, which makes it an essentially fragile coastline. This coast also suffers from a strong anthropic pressure marked by the presence of port and hotel infrastructures as well as the administrative and private buildings wich disturb sedimentary dynamics of the coastline. The coastal sector between Hillacondji and Grand-Popo, which for a while, is confronted to erosional phenomena of sandy band, which was the subject of the present study. Since 1980s, some short ears were erected on Togo coastline, 2 km faraway from the border withBenin (Hillacondji). Since their erection, erosion has been observed on Benin Hillacondji –Djondji coastline, but without being too critical. Following the rehabilitation of these ears in 2012, the erosion phenomena were aggravated on the costal band of Hillacondji -Djondji causing important socio-economic consequences.The purpose of this study was to assess the magnitude of the prevailing coastal erosion on the coastal band of Hillacondji –Djondji using data collected from field surveys and observation, as well as satellite images (Landsat).This study indicated that this section of coast is under a generalized coastal erosion with a significant acceleration since 2012. The coastline retreat over the four last years (between 2012 and 2016) was estimated at 16.46 m/year at Hillacondjibeach and at 5.13 m/year at Agoue beach. Only the coast segmentbetween Agoueand Avlo, showssince 1982 a dynamic balance followed sometimes by exceptional episodes of erosion. The Avlo-Djondji is confronted to a disturbance related to the mobility of the Mono River (embouchure) which is accompanied of violent and very destructive erosion phenomena.