Présentations Colloques

Oral Presentation
Session 2.02: Groundwater for sustainable water supplies in developing countries
Mapping groundwater availability and renewability in rural areas in Cambodia- a multi-disciplinary approach including geophysics, hydrogeology and geochemistry
The French Red-Cross in partnership with the Institut de Recherche pour le Developpement have been running projects since nearly ten years in order to improve water access in Cambodian rural communities. Indeed, there is more pressure on water resources since the population had more than tripled during the last decade. 12 % of households were still drinking surface water collected from ponds and a large number of households have to walk several kilometers in order to get safe water. **Geophysics surveys had first been carried out with Magnetic Resonance Sounding (MRS) and Time-Domain Electro-Magnetics (TDEM) to develop a strategy for sitting boreholes, and the success rate increased from 60 to 95 %. Then, a four years study of water resources was implemented through the monitoring of all the components of the water balance. Geophysical surveys were still carried out in parallel in order to support the mapping of aquifers. **The water budget method allowed the estimation of annual volumes of rainfall, actual evapotranspiration, surface runoff and groundwater recharge. Rainwater is mostly split into an evapotranspiration component (annual mean of 54 % of the rainfall) and a surface runoff component (mean of 49 % of the rainfall) as groundwater recharge is very low (mean of 1 % of the rainfall, i.e. from 10 to 700mm per year). Isotopes analysis suggested that recharge is direct and rapid, and simulations of pumping indicated that the aquifer can easily supply 100 L of drinking water per capita daily, even considering the estimated population in 2030.**Empirical relationships have been drawn between the specific yield from 5 pumping tests, 60 MRS soundings and more than 500 TDEM surveys. The results allow the creation of a 3D model of resistivities which is used to produce a storage map. This map highlights higher storage aquifers especially in the North and the East of Oddar Meanchey province where sandstones lie.**