Land clearance and long-term changes in the water balance in semiarid Niger 2 – Quantifying an increase in groundwater recharge using hydrogeophysical survey

Favreau, Guillaume, Boucher, Marie, Massuel, Sylvain, Vouillamoz, Jean-Michel, Descloitres, Marc, Leblanc, Marc, Tweed, Sarah, Nazoumou, Yahaya, Legchenko, Anatoly, and Cappelaere, Bernard (2007) Land clearance and long-term changes in the water balance in semiarid Niger 2 – Quantifying an increase in groundwater recharge using hydrogeophysical survey. In: Proceedings of the Second Internationnal AMMA Conference, pp. 292-293. From: Second Internationnal AMMA Conference, 26 - 30 November 2007, Karlsruhe, Germany.

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Abstract

In southwestern Niger, land clearance has resulted in an increase in surface runoff (Favreau et al., 1-) that has, in turn, resulted in steady rise in the groundwater reserves. As groundwater recharge occurs mostly where surface runoff concentrates, the dynamics of the water table is closely related to the drainage network connectivity. A mean rise of 4 m has occurred since the mid-1970s (+15% in aquifer reserves). According to previous geochemical estimates, the recharge rate was a few mm/year in the 1950s, whilst the prescnt recharge was over 20 mm/year. In order to improve these estimates, hydrogeophysical surveys (Time Domain Electromagnetic (TDEM) and Magnetic Resonance soundings (MRS)) were carried out on about 20 sites in 2005 and 2006. TDEM soundings helped to define the aquifer basement with a good accuracy (± I m). MRS were interpreted in terms of aquifer porosity and compared to pumping test data. The average MRS water content was 13% in volume of the aquifer, indicating that the total porosity is higher. The estimated recharge rate was therefore in the order of 0.2 mm/year before land clearance and is now at least 26 mm/year. In terms of water subtracted from atmospheric recycling, this represents a repeated loss in evapotranspiration of about 5% of current rainfall (26/560 mm of annual rainfall, Niamey). Although obviously small, this loss could possibly be significant for the water cycle at a regional scale. These observations and analyses also have implications for freshwater availability and food security in the Sahel.

Item ID: 4919
Item Type: Conference Item (Abstract / Summary)
Date Deposited: 06 Sep 2009 23:46
FoR Codes: 04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040603 Hydrogeology @ 100%
SEO Codes: 96 ENVIRONMENT > 9609 Land and Water Management > 960999 Land and Water Management of Environments not elsewhere classified @ 100%
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