Abstract
Due to small annual rainfall and high temperature, the water resource utilized for social activities in Djibouti is almost exclusively groundwater. Groundwater is collected through shallow wells in the porous sediments of the wadis with estimated thickness of several meters to about 20 meters, and through deeper wells in the fractured zone of the basaltic base rock. The network of wadis on the surface can be recognized by satellite imagery relatively clearly, but high geological ambiguity associated with the wadis and fractures, finding new good groundwater locations is not an easy task in Djibouti. In this study, using various field data collected, we have attempted to explore groundwater potential employing numerical hydrological model together with various field survey technologies. This paper introduces the first stage trials of numerical modeling using a terrestrial fluid flow simulator GETFLOWS, in which surface/subsurface coupled flows under precipitation/evapotranspiration are treated. For the target site, we selected the Ali Faren catchment, a part of large Ambouli watershed that extends southwest of Djibouti City. The Ali Faren catchment was discretized into a three dimensional model, reflecting the shape of wadi networks and basaltic surface. Giving initial estimates of hydrogeological parameters, several trial equilibrations/calibrations were made in order to check consistency between the hydrogeological setting and the calculated subsurface water condition. Using actual records of rainfall, the model showed occasional flush floods through the wadis and infiltration at relatively heavy rainfall.
