Assessment of Surface Water Potential Based On Watershed Modeling A Case of Sor Watershed, Ethiopia

Abstract

The successful understanding of surface water resources is fundamental to a country like Ethiopia for the growth of the national economy. Because, Surface water is the main source of water with only minimal dependence on utility. Knowing the potential, availability and use of surface water in Sor River would help to increase the productivity of agriculture. But, there is no detail study conducted to address surface water potential of this specified catchment with appropriate methods. Consequently, this study is aimed to estimate total surface water potential at the outlet of the Sor watershed and examine the associated uncertainty that can affect the accuracy in estimation of the surface water potential of a River. Sor River is one of the tributaries of Baro-Akobo River basin. According to watershed delineation using SWAT hydrological model an area of Sor watershed is about 1963.512 km2 . For assessing the surface water potential of Sor watershed, the Geographic Information System (GIS) based Soil and Water Assessment Tool (SWAT) has been used to assess surface water potential of Sor sub-basin. Model calibration and uncertainty analysis were carried with sequential uncertainty fitting (SUFI-2) that is linked with SWAT in calibration Uncertainty program known as SWAT-CUP. The calibration process was used to calibrate the model parameters using time series data from 1990 to 2005 and from 2006-2014 were used to validate the model using the sixteen parameters which is identified during sensitivity analysis. The calibration and validation of the model was found verygood as performance rating criteria value of coefficient of correlation (R2 ) and Nash Sutcliffe simulation efficiency (ENS) is found to be 0.80 and 0.74 for calibration and 0.79and 0.70 for validation respectively.In the equivalent order from the model uncertainties analysis the percentage of the simulated data within the uncertainty bound is just 49% for calibration and 44% for validation, which shows that there is uncertainty in the process. The result obtained from SWAT model, the watershed receives a mean annual rainfall 1700.7mm, Surface water runoff of the watershed 338.84 mm, and lateral soil flow is 143.73 mm. From total watershed area of 1963.512 km2 , 665.32MCm runoff was generated by the model from catchment annually. It has been concluded that the water demands from the River is not known, therefore further investigation is essential to use the available surface water potential of the watershed.