Properties of shallow thin regolith aquifers in sub-Saharan Africa: a case study from northwest Ethiopia

Pumping tests have been successfully conducted on shallow hand-dug wells in two areas of northwest Ethiopia. The drawdown and recovery data were analysed separately providing consistent results confirming suitability of methods. Hydraulic conductivity estimates ranged from 0.2 to 6.4 m/d (mean = 2.3 m/d, median = 1.6 m/d) in the dry season and ranged from 2.8 to 22.3 m/d (mean = 9.7 m/d, median = 6.5 m/d) in the wet season when the water-table was higher. This difference indicates the importance of excavating wells as deeply as possible to increase the likelihood of intercepting more transmissive (water-bearing) layers. Specific yield estimations have a wider range (0.00001 to 0.32) and are more uncertain though the mean of 0.09 (median of 0.08) is reasonable. Estimates of well yield average 0.5 l/s though this increases to >1 l/s in the wet season; giving opmitism that small-scale irrigation is achievable, therefore, potentially reducing the reliance on rain fed agriculture. These results from weathered basalt regolith add to the sparse available data on shallow groundwater resources in sub-Saharan Africa. Consistency of results from nearby and distant wells indicates homogeneity of shallow aquifer materials giving a high transferability of findings to other areas of Ethiopia. This knowledge of aquifer properties facilitates modelling for estimating impacts of climate variability and change, and for developing sustainable management strategies for shallow groundwater resources.