Tètchodiwèï Julie-Billard Yonouwinhi

CEA affiliates:

• CEA WACWISA African Center of Excellence for Water, Irrigation and Sustainable Agriculture, University of Tamale, Ghana
• University of Abomey-Calavi / CIPMA

Theme :
Diagnosis of solid transport in Lake Nokoué and its channels: Implementation of a quantitative model for assessing deposits.

Start date: 2021

Problem statement:
The World Water Forum's 2006 "Africa" regional report highlights the importance of siltation phenomena worldwide, with an average annual rate of reservoir volume loss of 0.5% to 1% due to sedimentation, exacerbated in Africa. The rivers that feed the lakes mobilize large quantities of material. The deposits resulting from this mobilization condemn lakes to rapid filling, especially when they have no outlet.

This filling is linked to the dynamics of lake watersheds, characterized by the erosion, transport and deposition of various materials; in addition, there are deposits due to anthropogenic activities carried out directly on these bodies of water. Benin boasts a fairly extensive network of more or less permanent waterways, and lakes that are extremely rich for the country. Lake Nokoué, the largest in Benin and one of the most important in Africa, is part of the RAMSAR 1018 site of unparalleled natural and cultural wealth. It consists of a marshy complex used as a passageway, but also for fishing and market gardening.

The maintenance of the pass since the construction of the port of Cotonou, uncontrolled dredging and acadja fishing techniques practised by the Toffin populations of Ganvié and Zogbo, have largely altered the hydrodynamic, physico-chemical and ecological conditions of the lake. In Benin, numerous anthropogenic activities are carried out on water bodies and watersheds, with no clear management policy in place to ensure that the various stakeholders assume their responsibilities.

These activities lead to the filling in of watercourses and lakes. Over the past decade, bathymetric work on Lake Nokoué has revealed a considerable reduction in its depth, mainly due to sedimentary input from activities in the watershed, which is in the throes of severe degradation.