Characterization of the hydrosedimentary dynamics of the estuary of Ouémé River in Cotonou, Benin.

Abstract

The present paper aims to characterize the hydrosedimentary dynamics of the estuary of Cotonou, a small channel of the ouémé river. This channel is used as a link of communication between the NokoueLakeand the Atlantic Ocean. So, this channel is an estuary of Ouémé River which has been the focal point of all the hydraulic and hydrologic exchanges between the lake and the ocean. That channel, artificial estuary, was built in 1885 to evacuate the floods of Nokoué lake, and to restrict this exchange between the lake and the ocean. To limit that exchange, one dam was built on the estuary in 1979. The construction of that dam had created a lot of environmental problems and had provocatedachangement of the hydraulic boundary conditions of the channel. The construction of the seaport of Cotonou, mainly the dam are the principal causes of the hydraulic changes which took place in the estuary. That dam is particularly responsible for the trapping of majority of the sediments discharged into the lagoon of cotonou by the Nokoué lake. This characterization of hydrosedimentary dynamics is based on the Shields parameter and the reading of the so-called Huljström diagram, on one part, and using the geometrical model established, depending of the bathymetry of the estuary, a modelization which leads to a better appreciation of the evolution of the sediments in the river.