Water Resource Developments and Flow Alteration in Didessa River Basin
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Date
2021-10
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Addis Ababa University
Abstract
Water demand increases due to population growth and the associated economic growth and irrigation factors for food production. Water becomes scarce as the amount of demand exceeds the available supply. Didessa River is the largest tributary of the Abbay river basin in terms of discharge capacity per unit area and still susceptible to supply-demand misbalance issues. The study's main objective was to assess the impact of water resource development and flow alteration in the Didessa river basin.
The Water Evaluation And Planning (WEAP21) tool was used to simulate the catchments and integrate supply sources and demand sites. The hydrological model performances manually for calibrated (1990-2008) and Validated (2009-2017) of NSE and R2 are 0.89 and 0.68, and 0 9 and 0.73 respectively. The crops water requirement and degree of hydrologic alteration respectively CROPWAT 8.0 and Indicator of Hydrologic Alteration (IHA) programs were used to estimates.
Two different scenario development were built. The first scenario is based on increasing population growth rate divided into Reference (1990-2017), small population growth rate (2018-2035), and higher population growth rate (2036-2050). The results indicated the unmet water demand, 0.74, 297. 87, and 784.46 in a million-meter cube. The second scenario was developed based on the expansion of irrigation activity, reference, short-term plan, and long-term plan remained the results indicate that the unmet water demand values: 0.195, 0.55, and 7.5-billion-meter cube in respectively.
The results of the first and second scenarios specify that the population growth rate and irrigation activities increased the unmet water demand also increased. It was shown that the degree of flow alteration was low in most months, and the Didessa near Dembi gauge station has high susceptibility to flow alteration than Didessa near Arjo gauge station. It was found that when the environmental flow has taken 20 up to 50 percent mean annual runoff, the unmet demand was reduced accordingly. Finally, it can be concluded that any future water development shall take into account all possible scenarios that can address environmental alteration and extra water requirements.
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Keywords
WEAP21, IHA, Didessa river basin, Flow Alteration, Scenarios, Unmet, Impact