WATER RESOURCE POTENTIAL INVESTIGATION OF LAKE HAWASSA WATERSHED BY USING A SOIL AND WATER ASSESSMENT TOOL (SWAT

Abstract

Uncertainties in information about fresh water resource potential have created a critical situation for many countries. Investigating spatiotemporal variability of water resources is, therefore, a critical initial step for water-resource management. Successful planning and management of water resources require the application of effective integrated water resources management (IWRM) models that can solve the encountering complex problems in these multi-disciplinary investigations. In this work, the water resources of Lake Hawassa watersheds were modeled using the Soil and Water Assessment Tool (SWAT), which is a continuous-time, semi-distributed, process-based model. The SWAT-CUP program was used for calibration/validation of the model with uncertainty analysis using the SUFI-2 (Sequential Uncertainty Fitting program) algorithm over the period of 1990- 2015 at one gauge station. Parameter transfer method was used from gauged (Tikurwuha) sub catchment to ungauged one. The performance of the SWAT model was evaluated through sensitivity analysis, calibration, and validation. Ten flow parameters were identified to be sensitive for the stream flow of the study area and used for model calibration. The model calibration was carried out using observed stream flow data from 1995 to 2010 and a validation period from 2011 to 2015 years. Both the calibration and validation results showed satisfactory match between measured and simulated stream flow data with the coefficient of determination (R2 ) of 0.71 and Nash-Sutcliffe efficiency (NSE) of 0.66 for the calibration, and R2 of 0.64 and NSE of 0.59 of the validation period. The results reveal that the annual blue-water potential (water yield and deep aquifer recharge) of Lake Hawassa Watershed is 854 million m3 , Whereas the green-water flow (actual evapotranspiration) (ET) is 629 million m3 and green water storage (soil moisture) is 82 million m3 . Watersheds located around Wondo-Genet yield more blue-water resources compared to watersheds at the western side. The model highlights the water potential of the catchment under current circumstances and gives an insight into its spatiotemporal distribution over the watershed. This study provides a strong basis for the forthcoming studies concerning better water-resources management practices, climate change, and water-quality studies, as well as other socio-economic scenario analyses in the region.