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Wondmyibza Tsegaye Bayou, Stefan Wohnlich, Mebruk Mohammed, Tenalem Ayenew

• The Sor and Gebba watershed has undergone several natural and anthropogenic changes, as evidenced by the physical alterations and artificial mismanagement of water resources in the watershed. These situations alter the underground storage aquifer contribution to the streams. Thus, understanding baseflow of the watershed enables us to identify the groundwater system potential and dynamicity. The main objective of this research is to estimate baseflow using several hydrograph analysis techniques as there was neither an organized groundwater resources research carried out at the watershed level nor studies on various methods on estimation of baseflow contribution to these streams. Hence, this research involves estimating baseflow from daily streamflow data using the manual hydrograph analysis technique, Flow Duration Curve (FDC), timeplot, Web-based Hydrograph Analysis Tool (WHAT), the US Geological Survey Groundwater Toolbox (USGS GW Toolbox), and the Baseflow index program (BFI+). The analysis result shows that most automated filtering techniques used with presumed parameters have estimated above-average baseflow compared to the FDC and the manual hydrograph analysis techniques. Moreover, FDC and manual hydrograph analysis resulted in a below-average value of underground storage aquifer contribution to streamflow. The BFI values are proportional for the Sor and Gebba streams and estimated about 33% for the entire watershed.