Physical Characterization and Evaluation of the Water Potential of the Watershed of the Ferlo Fossil Valley, Senegal: Louga Area

This study is an evaluation of the water potential of the Ferlo fossil valley in the Louga area in Senegal. It consisted in determining the volume of water that could be mobilized at the level of a confluence point of the waters according to the flow lines, where a dam would be placed to create a reservoir. This volume of mobilizable water was compared to the average water consumption of the area in order to evaluate its adequacy or not. To do this, a delineation, physical characterization and mapping of the Ferlo watershed was done using Google Earth, Global Mapper and Arc GIS softwares. A catchment area of 28,754 sq·km was obtained with a perimeter of 976 km, an average slope of 0.52% and a hydraulic length of 336 km. Then the decennial runoff of the watershed was calculated using the CIEH method, this flow is estimated at 1120 cm/s. On the basis of this flow, the annual volume of water that can be mobilized was estimated at 11,089,758 cm per year with a solid deposits of 93 cm per year. The conclusions reached are that there is a lack of mobilizable water resources in the area and that the entire fossil valley needs to be rewatered to provide a sustainable alternative water source.

Risk Assessment of Rainwater Overflow from Lake Warouwaye in the Case of a Ten-Year Rainfall in Yeumbeul North, Senegal

This study is a part of a global approach in which, the main purpose is to understand the reasons behind the upsurge of flood events in the peri-urban area of the city of Dakar. Hydrological and hydraulics simulations were carried out to assess the risks of overflowing of the Lake Warouwaye after a so-called exceptional rain. Data were collected through field surveys, as well as site observations of dwellings before and after rain episodes. The simulations were performed using EPA’s Storm Water Management Model (SWMM) software with input data obtained from sub-software and supervisory applications such as Google Earth, Excel, and Global Mapper. The simulation results show factors of natural and anthropogenic origin may contribute to dysfunction hydrological elements such as the watershed capacity to drain and store water. In light of the results of this study, institutional governance efforts are to be made and to be sustained in order to reverse the tendency to occupy rainwater natural flow channels. It will also be necessary to involve the first actors who are the potential victims of flooding caused by the recurrent overflow of reservoirs.