Groundwater recharge and contribution to the tana sub-basin, upper blue Nile basin, Ethiopia

Abstract

The Tana sub-basin exhibits one of the huge groundwater reserve zones in Ethiopia. While there is effective three months of precipitation, Lake Tana receives year-round recharge from the four major rivers in the sub-basin: Gilgel Abay, Gumara, Ribb, and Megech. Hence, the groundwater contribution to the Lake Tana is quite important to the aquifer-dependent ecosystem and environmental flow requirement in the area. However, the contribution of the groundwater resource to the Lake Tana water body is not well studied, and useful information for development planning and management is not available. The purpose of this study was to develop information that can better inform decision making on groundwater abstraction and/or lake water uses in the Tana sub-basin considering the volume of the groundwater contribution to the Lake Tana water body. Accordingly, the study combined stream flow simulation and baseflow separation. The stream flows at the junction of the lake water body are generated by the application of Soil and Water Assessment Tool (SWAT). The groundwater contribution of the streams is defined by baseflow separation using a reclusive digital filter method. The groundwater contribution to the Lake Tana water is through lateral flow from the vadose zone and return flow to shallow aquifers. The contribution of the four major rivers’ catchment area; Gilgel Abay, Gumera, Ribb, and Megech Rivers, is 718, 414, 451, and 350 mm/year, respectively. This accounts up to 60 % of the total annual in flow to the Lake Tana water body through stream flow.