Hydrogeology and groundwater flow in a basalt-capped Mesozoic sedimentary series of the Ethiopian highlands.

A hydrogeological study was undertaken in the Zenako-Argaka catchment, near Hagere Selam in Tigray,
northern Ethiopia, during the rainy season of 2006. A geological map was produced through geophysical measurements and ?eld observations, and a fracture zone identi?ed in the north west of the catchment. A perched water table was found within the Trap Basalt series above the laterized upper Aram Aradam Sandstones. A map of this water table was compiled. Water-level variation during the measurement period was at least 4.5m. Variation in basal ?ow for the whole catchment for the measurement period was between 12 and 276m3/day. A groundwater ?ow model was produced using Visual MODFLOW, indicating the general direction of ?ow to be towards the south, and illustrating that the waterways have only a limited in?uence on groundwater ?ow. The soil water budget was calculated for the period 1995-2006, which showed the important in?uence of the distribution of rainfall in time. Although Hagere Selam received some 724mm of rainfall per year over this period, the strong seasonal variation in rainfall meant there was a water de?cit for on average 10months per year.

Keywords:hydrogeology, groundwater flow, ethiopia, groundwater recharge / water budget