Assessment of Water Balance of Deme Watershed, Omo-Gibe Basin, Ethiopia Using SWAT Model and ARC-GIS for Water Resources Management

Abstract

To deal with water management issues, one must analyse and quantify the different elements of hydrologic processes taking place within the area of interest. Obviously, this analysis must be carried out on a watershed basis because all these process are taking place within individual micro watersheds. Only after understanding the spatial and temporal variation and the interaction of these hydrologic components one can scientifically formulate strategies for water conservation. To achieve this goal the choice and use of an appropriate watershed model is a must. All the thematic maps and attribute information of the watershed have been collected from various Government agencies. SWAT model has been set up for the Deme watershed by inputting the digital thematic maps, physical properties of soil and climatic parameters. Total area of the watershed corresponding to the outlet chosen at Deme watershed is 11284.35km 2 and its elevation varies from 1138 to 3269m. Calibration and validation of the model have been done by comparing the river flow prediction with the observed values. Nash Sutcliff Efficiency (NSE), coefficient of determination (R 2) and Percent bias (PBIAS) has given very high values for the calibration 0.75, 0.75 and-0.7% respectively and validation 0.73, 0.74 and 6.3% respectively. The calibrated model has been used to predict the important hydrologic processes. The water balance components of Deme watershed resulted PET 388.5mm, Evaporation and transpiration 293.8mm, Precipitation 1147.5mm, Average curve number 76.38, Surface runoff 189.7mm, Revap from shallow aquifer 7.7mm, Percolation to shallow aquifer 37.59mm, Lateral flow 624.33mm and Recharge to deep aquifer 0.28mm. The study has revealed that SWAT model can effectively be used in the simulation of river flow and for predicting the water balance of a watershed. Water balance information of the basin is of great use in planning water conservation, drainage and flood control.