Arjo Didessa Reservoir Water Evaluation and Allocation System

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Addis Ababa University


The Abay basin is one of the Ethiopian basins endowed with abundant surface water and groundwater resources that require proper management and have to be wisely utilized in a sustainable manner. Didessa River is one of the tributary of Abay basin. Evaluating the seasonal variation of this river will provide management and fair distribution of water resources in Didessa catchment. Currently Arjo Didessa earthen dam is the reservoir found in the Upper Didessa River being utilized for Irrigation uses and in addition to irrigation uses different water users are found in Didessa catchment that will gain water from the same source. For this reason it needs evaluation and planning of the Didessa river water. To address water resources fairly to all users requires technical issues and specialized tools Arc view GIS tool to obtain hydrological and physical parameters and spatial information, Global Mapper to manipulate the DEM data in line with the shape files of the river basin and WEAP (water evaluation and planning) model to assess the consequences of climate change and irrigation expansion on current and future water use practices of Arjo reservoir. Records of hydrology and meteorological data have been statistically tested and arranged as an input data source to fit the model. Meteorological and grid climatic data were correlated with multi-regression and distribution mapping (DM) method respectively. The demand and the supply of water resource, baseline data and the future development activities of the area were compared using the mainly two different scenarios climate change and irrigation expansion. This study analyzed the model calibration, validation and its statistical measure were seen and the result shows that it is very good and the model can simulate the current and the future scenarios. After all of this done, the results revealed that unless the minimum flow requirements are maintained, the future irrigation demands are unmet in more or less. Due to the climate change the volume of reservoir evaporation in the (2016-2030) period was increased by 1.5%, in 2031-2050 periods was increased to 3.1%, and 2051-2080 period was increased to 4.3% when comparing with the current scenario. While compared with the baseline period, the first 15 years reservoir evaporation will increase but the Arjo Didessa Reservoir water has full supplement. There should be more detailed water resource management activity, including sustainable abstractions. In addition to this, the new projects on the study area have to construct for additional demand supply or supply with irrigation expansions



groundwater resources, Didessa River, Arjo Didessa reservoir water Evaluation