Optimization of surface water allocations in a prospective vision : application of the WEAP model in the Ivory Coast Aghien lagoon watershed

The Aghien lagoon catchment area (365 km²) is largely based on the Ivorian sedimentary basin (68%) and the rest (32%) on the crystalline and crystallophyllous basement. Both coastal and peri-urban basin of the District of Abidjan, the Aghien lagoon watershed is subject to anarchic clearing and increasing urbanization, in addition to being affected by deficient rainfall conditions, since the late 1960s. This watershed, which contains the largest freshwater reserve in the lagoon near the large urban area of Abidjan, has been identified as a potential source of additional drinking water production. The objective of this study is to evaluate the quantitative and qualitative suitability of the waters of this lagoon for the sustainable production of drinking water for the District of Abidjan. In a broader perspective, with the current signs of failure of the water table that supplies the city of Abidjan with water, the Aghien lagoon constitutes one of the ways and one of the hopes for the water supply of the gigantic agglomeration of Abidjan in the years to come, in order to solve the major issues in terms of water resources and drinking water supply, issues that are accentuated by the densification of the population and the effects of the climate change In terms of approach, the aim is to develop, within the framework of WEAP 21 (Water Evaluation and Planning), a decision support system for the sustainable management (current and future by 2050) of this resource through quantitative and qualitative management scenarios, by comparing the evolution of demand to that of supply. This method is based on hydro-climatic data sets and survey data from in situ measurement campaigns; it also integrates a prospective vision of water resources, by extending current trends to 2050, according to alternative scenarios on supply and demand.