Evolution récente de la ressource en eau consécutive aux changements climatiques et environnementaux du sud-ouest Niger. Modélisation des eaux de surface et souterraines du bassin du kori de Dantiandou sur la période 1992-2003

Abstract : Near Niamey (Niger), a continuous rise in the groundwater level has been evidenced in spite of the drought that has been occurring for the last 30 years. Heavy environmental changes since 1950 have induced a runoff increase and indirectly the enhancement of the groundwater recharge. In order to better understand this rise, the strategy used in this study was to link runoff modelling with groundwater measurements because of the lack of significant runoff data at large scale and the lack of relation between rainfall and recharge.
To this aim, a regionalisation of the storm runoff production over a 5000 km² domain made of hundreds of ungauged, small endoreic surface-water catchments has been conducted. This is attempted through upscaling of an existing fine-scale, physically-based hydrologic model : abc-rwf. The upscaled model named Zarbhy combines three modelling components in a nested structure. A first component of rainfall filtering produces a very effective runoff-controlling storm descriptor. A relatively simple runoff functional structure can reproduce the fine-scale distributed model behaviour for a given basin. Finally, regionalization with respect to a subset of synthetic physiographic catchment descriptors allows to generalize the simplified runoff modelling structure within a global, non linear multi-catchment functional formulation. Runoff computation allows indirect recharge forcing for the simulation of the water table rise during the 1992-2003 period.
Coupled geophysical and geochemical survey and runoff modelling has evidenced the leaching of a mineralised band in the unsaturated zone situated between 5 and 10 m deep, systematically under sandy channels of an alluvial fan in the Wankama experimental basin. This promising experiment calls for further investigations for a better characterisation of local recharge processes.
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Submitted on : Tuesday, November 22, 2005 - 5:46:03 PM
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Sylvain Massuel. Evolution récente de la ressource en eau consécutive aux changements climatiques et environnementaux du sud-ouest Niger. Modélisation des eaux de surface et souterraines du bassin du kori de Dantiandou sur la période 1992-2003. Hydrologie. Université Montpellier II - Sciences et Techniques du Languedoc, 2005. Français. ⟨tel-00011097⟩

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