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International symposium - Aquifers Systems Management - 30 may-1th june 2006, Dijon, France Colloque international - Gestion des grands aquifères - 30 mai-1er juin 2006, Dijon, France

DARCY 45 Etude hydrogéologique et modélisation mathématique du système aquifère du bassin sédimentaire de Taoudeni au Burkina Faso
DEROUANE Johan 1 & DAKOURE Denis
2

1 MRW DGRNE Division de l’Eau, Jambes,Belgique, j.derouane@mrw.wallonie.be 2 MAHRH DGAEP Programme VREO, Bobo-Dioulasso, Burkina Faso, vreo@fasonet.bf

Abstract
The south-west of Burkina Faso shares with the south of Mali a regional aquifer system that forms part of West Africa’s large sedimentary basin of Taoudeni. With a surface area of around 40,000 km? inside Burkina Faso, and a depth that can reach more than 2,000 meters, thissedimentary aquifer system provides most of the water resources exploited for human (drinking water) and economic (mainly agriculture) needs in the country. In a critical semi-arid context characterised by the notable decrease in pluviometry observed in the last 40 years, and by a demographic explosion resulting in a highly increased need of water for human consumption and for economic development,the management of this important groundwater resource has become a priority not only for the Burkina Faso authorities, but also for the international community. A hydrogeological multi-disciplinary approach, combining amongst others stratigraphy, hydrodynamic field-data, geochemistry and isotopic techniques with geological and hydrogeological modeling, is being implemented to improve theknowledge of the aquifer system and the efficiency of its management. While geochemistry and isotopic techniques performed in the studied area do not provide convincing elements to consider the existence of individualized aquifers inside the identified sedimentary geological formations, the question of vertical hydraulic continuity over the whole part of the sedimentary basin in Burkina Faso stillremains, as well as the estimation of the effective recharge rate. The observed piezometry of the system shows a typical behavior of a drainage basin with local flows discharging into Burkina Faso’s main rivers, but considering the low relief of the topography compared with the depth of the base of the flow system, a regional flow system towards the Bani and Niger rivers in Mali - as a main dischargearea - can not be excluded according to Toth’s model approach. A conceptual representation of the hydrogeological context, based on the results and interpretations of the collected field data, is developed and implemented into a geological (aquifer geometry) and groundwater flow model. Further studies, crossing the borderline with Mali, should contribute to validate some of those assumptions that arestill to be considered as conceptual hypotheses, and should lead to improve the current knowledge of this important aquifer system.

Contexte de gestion et d’exploitation des ressources en eau souterraine au Burkina Faso Le Burkina Faso, pays enclavé au centre de l’Afrique de l’Ouest, compte environ 12 millions d’habitants dont 80% vivent en milieu rural. Situé en zone aride à semi-aride, sasuperficie est de 274.000 km2. La majeure partie du territoire est constituée par un plateau latéritique d’une altitude moyenne de 300 mètres, qui s’incline du Nord-Est au Sud-Ouest. Le climat, de type soudano-sahélien, est caractérisé par des variations pluviométriques spatiales et interannuelles considérables, allant de 350 mm au Nord (climat sahélien) à 1100 mm au SudOuest (climat sud-soudanien).La saison des pluies s’étale sur trois mois au Nord et sur sept mois au Sud-Ouest. Le réseau hydrographique est réparti en quatre bassins versants nationaux (Comoé, Mouhoun, Nakambé et Niger) et comprend deux cours d’eau majeurs permanents : la Comoé et le Mouhoun.
Geological and hydrogeological modelling / Modélisation géologique et hydrogéologique
Etude hydrogéologique et modélisation...
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