ESTIMATION OF GROUNDWATER RECHARGE USING WETSPASS MODEL AND BASE FLOW SEPARATION METHOD: CASE STUDY OF GIDABO CATCHMENT IN RIFT VALLEY BASIN, ETHIOPIA

Abstract

Groundwater is a precious fresh natural resource in sub-surface formations that is very important for the water supply utilization of human beings. However, abstraction and consumption of the groundwater in the study area are not based on the understanding of the seasonal and annual amount of recharge the study area received as well as the effect of land use change and other variables on the recharging process. So, this study aims to estimate groundwater recharge of the Gidabo catchment using the WetSpass model and base flow separation method. Long-term hydrometeorological data and physical characteristics of the catchment such as land use/land cover, soil type, topography, groundwater level, and slope were used as input to the model. The available data of five river gauging stations in the catchment were used to validate the WetSpass model for its applicability in simulating the long-term averaged annual water balance using the baseflow separation method. The results showed that the long-term mean annual rainfall of 1272.23mm was partitioned into 17.61% of surface runoff (Qo), and 74.05% of actual evapotranspiration, and 8.01% of the water annually recharges the groundwater system. And also, from the baseflow separation method the area receives 123mm recharge annually, and this accounts for 9.75% of the mean annual precipitation of the catchment. According to the model results, the hydro-meteorological and geospatial physical variability of the area controls the spatial and temporal variation of water balance components of the catchment. Generally, analysis of the simulated results indicate that WetSpass works well to simulate the components of the hydrological balance for the Gidabo catchment and helps for sustainable management of the Gidabo watershed to enhance thegroundwater recharg