Abstract:
Increasing competition for water across sectors (agriculture, industries, domestic, and power
generation) increases the importance of the river basin as the appropriate unit of analysis to
address the challenges facing water resources management; and the basin requires proper
planning and management of water resources available to provide essential information for
policy makers in their resource allocation decisions. Hence, this study mainly focuses on water
balance and reservoir operation analysis for optimal power production for cascaded hydropower
plants in the upper Omo-Gibe river basin. SWAT model was used to simulate the current inflow
to the cascade reservoirs. The performance of the model has been evaluated through calibration
and validation process. Model sensitivity analysis at Abelti gauging station shows ESCO, Soil_Z
and Alpha_Bf as the most sensitive parameters. The overall evaluation indicated that SWAT
model satisfactorily simulates river flows in the study area with R
2
of 0.84 and NSE of 0.81
during calibration. During validation, R
2
of 0.79 and NSE of 0.69 were obtained.
HEC-ResSim (Hydrologic Engineering Center-Reservoir System Simulation) was used to
simulate water allocation and operation of existing, ongoing and planned reservoirs in Omo-Gibe
basin. Three water resources development scenarios were applied to analyze reservoir operation
of the basin (Scenario T, Scenario A and Scenario B). Scenario-A result shows that an average
annual energy output of 786.97, 1806.40 and 6446.00 GWh/year for Gibe I, Gibe II and Gibe III
respectively. The mean maximum pool level in Gilgel Gibe-I and Gibe-III was estimated to be
1671 m.a.s.l and 891.9m.a.s.l.in October whereas the minimum mean pool level was estimated to
be 1658.5 m.a.s.l. in May and 859.6m.a.s.l.in June respectively. In scenario B, due to regulation
of flow at upstream, the annual power production in Gibe III was increased and the simulation
result shows an average annual energy production of 6514.00 GWh/year. The mean maximum
pool level in Gibe-III was 895m.a.s.l.in September whereas the minimum mean pool level in
Gibe-III pool was 860 m.a.s.l. in July.
