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Rheinischen Friedrich-Wihelm-Universität Bonn (2007)

Groundwater potential to supply population demand within the Kompienga dam basin in Burkina Faso

Sandwidi, Wennegouda Jean Pierre

Titre : Groundwater potential to supply population demand within the Kompienga dam basin in Burkina Faso

Auteur : Sandwidi, Wennegouda Jean Pierre

Université de soutenance : Rheinischen Friedrich-Wihelm-Universität Bonn

Grade : Doktor der Agrarwissenschaften 2007

Résumé
Groundwater recharge is constrained by various factors with rainfall playing a key role. The Kompienga dam basin located in southeastern Burkina Faso displays semi-arid climatic conditions with rainfall occurring five months per year. The average long-term (1959-2005) mean annual rainfall amounted to 830.2 mm with high temporal and spatial variability. During the year, evaporation always exceeds rainfall, except for a few months in the rainy season when recharge can take place in the basin. In addition, the crystalline rocks of granites and amphibolites mainly underlying the basin have a poor water storage capacity. Therefore, groundwater recharge in the basin is estimated to be as low as 43.9 mm, which represents 5.3% of the rainfall in 2005 for a potential groundwater volume of 259.5 million m³. The estimation based on the water balance method, the chloride mass balance method and the water table fluctuation method shows that the basin recharge is mostly through matrix flow with considerable spatial variability based on soil textures, crystalline rock fracturing, land-use/land-cover and topography. Thus, preferential flow processes are dominant in the basin recharge in the southwestern part around Tanyélé, where the chloride concentration in the groundwater is about that in rainwater. Annual recharge in the basin is determined by an annual rainfall threshold ranging between 314.3 mm and 336.6 mm reached during the first two to three months of the rains. This relationship provided the equation for deriving annual groundwater recharge in the basin. According to Eddy correlation measurements, actual evaporation in the basin depletes the aquifers at an average rate of 0.6 mm per day during the dry season. This situation contributes to the reduction of the groundwater resources and limits the possibilities of developing these resources to improve the population’s livelihoods. The basin population in 2005 was 270 000 inhabitants living in 15 departments in 5 provinces, and water withdrawal was estimated at an average rate of 76 l/c/d (including livestock watering) in the dry season period. This represents 5 million m³ of water, making up 2 % of the annual recharge to the aquifers. In anticipation of decreasing rainfall and increasing population in the Kompienga dam basin, scenarios of recharges against withdrawals show that the annual recharge will support the demand for water till 2030 at a supply rate of 25 l/c/d from 1260 functional boreholes operating 12 hours per day at an average unit yield of 1 m³ per hour. The nationally formulated norm for rural water provision of 20 l/c/d was found to respond to basic needs only, and 35 l/c/d is considered the required supply rate especially from March to May when the water demand is highest. Therefore, the revision of the national norm and policy target for rural water supply is recommended

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