Modeling Long-Term Water Allocation and Analysis of Alternative Strategic Scenarios in the Catchment Area of Bilate River, Rift Valley Lakes Basin, Ethiopia

A water shortage stress might have resulted from the extensive water resources development plan in the Bilate catchment owing to the rapidly growing population, irrigation development expansion, climatic variability, and socioeconomic development. Furthermore, the lack of sufficient knowledge about available water resources and lack of coordination in water resources management skills in the basin often aggravates the competition of fixed waterresources among the users. Therefore, modeling long-term water allocation should be implemented to determine the optimal allocation of water resources, maximize the overall benefits without compromising ecological requirements, and propose mitigation measures that may alleviate the problem of water scarcity during peak demand periods. The Water Evaluation and Planning (WEAP) model is generally used in the formulation and evaluation of alternative plansfor responding to water-related problems and water resources developments. To assist in the assessment of spatialtemporal streamflow simulations within watersheds, the Soil and Water Assessment Tool (SWAT) employed in the Bilate River and its sub-catchments. The Indicators of Hydrologic Alteration (IHA) and CROPWAT 8.0 software programs were used to estimate streamflow requirement (IFR) and the crop water requirement, respectively. Three development scenarios include the agricultural and socio-economic development effect, climatic change, and alternatives that were built in the long-term planning horizons (2013-2050). The modeling water allocation for each sub-catchment was done by considering the Ethiopian water allocation and apportionment criteria and water act priority order. The result revealed that agriculture growth (increasing irrigation projects) and socio-economic development caused a significant increase in water demand. Hence unmet water demands in different parts of the catchments were increased. Similarly, the effect of climatic variation scenarios has been increased unmet demands in the middle year of the planning horizon(2030-2050). Therefore, developing adaptation strategies scenarios helps to mitigate water scarcity and improve water availability for productive use.