MODELING OF SURFACE WATER RESOURCES FOR WATER ALLOCATION: A CASE STUDY IN UPPER GIDABO WATERSHED, GIDABO SUB BASIN, ETHIOPIA

Abstract

The processes of population increase, urbanization, industrialization, and dependency ratio has resulted in a rapid demand increase for water resources in the developing world. Water managers in the watershed of the developing world face the increasingly difficult task of allocating the limited water resources among competing users for fulfilling their demands due to difference in available resources and water demand increment. Water resources management has limited in the Upper Gidabo watershed and there is traditional water allocation are vastly practiced. This was due to lack of sufficient awareness about available water resources and management in watersheds. Understanding the potential and use of surface water in upper Gidabo would help to increase the productivity of Agriculture and other sectors, to improve the traditional water management system. Therefore the objective of this study was to Modeling of surface water resources for water allocation under developed scenarios for maximizing overall benefits without compromising ecological requirements in the Upper Gidabo watershed in Gidabo sub basin. To achieve the aim of this study soil and water assessment tool (SWAT) model was used to determine the available surface water resources of the watershed after sensitivity analysis, calibration and validation of the model by SWAT_CUP sufi-2 algorithm. The simulated result revealed that the total average surface water potential from the watershed was 773.5 MCM annually during the study period (2021). Both the calibration and validation result for Aposto and kolla gauging station showed a good performance with a value of R2 and NSE of 0.83 and 0.65 for calibration and 0.81 and 0.6 for validation in Aposto and 0.79 and 0.62 for calibration and 0.78 and 0.61 for validation in Kolla gauging station, respectively. After this Water Evaluation and Planning (WEAP) model was used to assess water demands. To assess irrigation water requirement of the sixteen (16) crop types CROPWAT 8.0 software was used. After assessing the currently existing demands Different scenarios were also developed to determine the future water demand, and unmet demand from overall time period of 2021-2050, This scenarios namely: reference, population growth and increased water demand scenario was established to determine increasing demands under increasing human as well as Livestock population, agricultural areas and different industrial activities. The current (2021) utilization is about 110.4 MCM for consumptive use and non-consumptive (EFR) use, For EFR 10% considered from available flow to maintain ecological functioning and water resource development in the watershed. The current demands fully met with available flows and for scenarios the assessed total annual water demand may be expected to be 126 MCM, 195.1 MCM and 341.8 MCM for the reference, high population growth, and increased water demand scenarios, except increased water demand scenario the other scenarios is met fully, It is appropriate to shape more effective policies and regulations in the area for effective water resources management in reducing water shortage and achieving downstream water needs in the future