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Titre : | Hydrogéologie du bassin de l'Ouémé supérieur : Ressources en eaux souterraines |
Auteurs : | Agathe LE FLOC'H ; Timothée HUGOT ; Timothée HUGOT |
Type de document : | Projet d'initiation à la recherche apprenti |
Concepts : |
BENIN
HYDROGEOLOGIE AQUIFERE |
Résumé : | In a Sudanian climatic context characterized by a dry and a rainy season, influenced by the west African monsoon, the water scarcity in some region is a major problem. Hence, a French foundation named « Le Coeur de Vivescia », asked us to identify every underground water stock in order to irrigate the crops localized in some parts of the Oueme basin. Since most of the plots are localized in the Donga basin (a small part in the northeast of Oueme basin), a particular attention has been paid to this area. A second spot situated in the south of Oueme basin, around the city of Manigri, has been studied because 3 isolated plots are located there. After a brief summary of the social, climatic and geographical context, the first part dedicated on geology allowed us to observe area's structure. Under some potential recent alluvium and aeolian deposit, a laterite layer with a thickness between 0 m and 25 m is present on the study area in the form of alteration silts and lateritic armour. This layer is on top of the magmatic and metamorphic basement rock, composed by Dahomeyen granite and gneiss, which is showing up to the surface on some points. Underground water stock is generally located at the interface of two different geological layers, the aquifer had been searched between the top of the basement and the bottom of the laterite layer. A second part about hydrology and hydrogeology focus on this aquifer. Thanks to AMMA-CATCH database, a cross analysis of rainfall, river-gauging and piezometers, added to a bibliographic work on the area, make it possible to identify the hydrogeological function of this laterite aquifer. This phreatic table being interrupted, it is not the main source of surface's water flow. Vegetal evaporation and ground transpiration are the main way to empty the aquifer. The way of filling up the phreatic table is through wildlife macroporosity, when the soil is saturated. Looking at the water resources needed by the farmers, studied in a third part, the laterite's aquifer seems to be usable. Yet, no precise evaluation of water resource had been done, due to aquifer's discontinuity. A second stock had been found into the broken basement. However, this water being motionless, it can degrade its quality. Another solution would be to install rainwater tanks next to the plots, which could be a temporary resource in case of a water shortage. Geophysical campaigns could be interesting in order to quantify the depths and the height of water resources precisely on the plot helped by « Le Coeur de Vivescia ». |
Spécialité : | Géologie |
Numéro de promo : | 81 |
numéro MIR : | 19 |