Evaluation of the Optimum Flooding Control and Water use Scenario for Agricultural Development along Senegal River, Mauritania

Recently, rice consumption increases rapidly in several West African countries as the staple food. Although, these consumptions are still covered by importation, government of each countries expects to strengthen domestic rice production from the food security of viewpoint. Paddy fields in West African countries are mostly irrigated by abundant water resource in large river.

However, productivity and number of rice farmers are sluggish due to the lack of water management system in these rivers. Risk of flooding and high fluctuation of water level between rain and dry season decrease the farmers’ motivation of agricultural investment. In order to develop the domestic food production, stable access to water resource should be achieved by construction of hydraulic facilities.

In our study, we try to evaluate the optimum flooding control scenario by computational fluid dynamics (CFD) simulation conducted to Senegal River bank in Mauritania as the case study.

Sahara Dessert is occupied 80% of Mauritanian lands. Owing to this geographic constraint, self-sufficiency rate of rice is sluggish as 50%. Government expects to improve the rice production in southern region where Senegal River flows. However, river flooding occurs frequently and damages rice farming. As the solution for that, we suggested to convey the flooding water to Lake R’kiz which locates near the river as the dry lake for flood mitigation. Moreover, these storage water can be used for the irrigation in the dry season.

Based on this suggestion, flood control impact was evaluated by comparison of CFD simulation results between current condition without water conveyance and consideration of water conveyance. Flood control impact is affected by the scale of flooding event, conveyance timing of flooding water and inflow rates to Lake R’kiz from conveyance channel. For considering these factors, some types of weirs were introduced at entrance to Lake R’kiz in the water conveyance channel.

In addition, double cropping system of rice is promoted by taking advantage of the mild climate. In order to improve that, certain growth stages of rice which are damaged seriously by flooding in rain season and required irrigation water in dry season were extracted from rice cultivation schedule data. Each growth stage was compared with simulation results of inundation area and water storage quantity in Lake R’kiz to evaluate the optimum flood control scenario.