Modelling of the Hydrogeological Behaviour of the Tassette Aquifer: Study of the Possibilities of Exploiting This Aquifer as an Alternative against the Limestone Problem in the Commune of Thies

Abstract

Senegal's drinking water supply comes on the one hand from groundwater and mainly from Maastrichtian and Paleocene aquifers. The Tassette area included in the Thies region has such potential that the Paleocene is currently exploited to cover a certain part of Dakar's important water needs. In addition, the city of Thies is itself confronted with the problems of limestone present in its drinking water and generally creating problems of scaling pipes. A water transfer is therefore a possible option to deal with this situation. This study will consist of modelling the Tassette aquifer to determine if it will cover Thies' water needs over a period of 20 years. To assess the responses of the groundwater to pumping at this level and the changes that may occur, a numerical hydrogeological model is necessary. In order to have a better overview of the area, boreholes and piezometric tests were carried out, highlighting the different characteristics of the aquifer and the water it contains. Based on these, the model was developed according to a mesh system and more precisely by discretization and simulation according to the finite difference method from the Visual Modflow Flex software. The results observed for this modelling show that the city of Thies cannot be supplied as a whole. This mining model also causes brackish water intrusion. On the other hand, the additional withdrawal of a certain quantity of water compared to the current situation does not have as great negative impacts and would still partially meet the expectations of this modelling.