Modeling The Water Balance, Reservoir Operation and Simulation Analysis for Cascaded Hydropower Plants: A Case Study of Upper Genale-Dawa River Basin

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Date

2019-06

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Addis Ababa University

Abstract

This research is intended to assure the equilibrium between energy production and consumption from hydroelectric energy. Hydroelectric power plant development on GenaleDawa River basin is, a part of development plan for Ethiopian energy production. Modeling of Water balance and Reservoir Operation is frequently required in Hydraulic engineering for reservoir management and to control fluctuation of water. This study mainly focuses on water balance and reservoir operation analysis for cascaded hydropower plants in the Genale-Dawa river basin by using HEC-ResSim and HEC-HMS model. The stream flow generation were estimated by using HEC-HMS model to enhance the water balance components at Genale cascade reservoirs in the semi-ungauged parts of upper river basins. A Digital Elevation Model (DEM) with 30 × 30 resolution of the study area was used to extract the physical characteristics of watersheds using Arc-Hydro and the Geospatial Hydrologic Model Extension HEC-GeoHMS. Then the HEC-HMS program was selected for this study, to attain the water balance components of the basin due to its versatility, capability for flow generation, automatic parameter optimization and its connection with GIS through HEC-GeoHMS. HEC-ResSim (Hydrologic Engineering Center-Reservoir System Simulation) was used to simulate the water allocation and operation of ongoing and planned reservoirs system in Genale-Dawa River basin. It is capable of modeling any reservoir system and designed to perform reservoir operation modeling at single or multi reservoir system. The performance of the model has been evaluated through calibration and validation process. The HEC-HMS model was calibrated and validated on a monthly time scale, with reference to Chena-Mansa gauging station to estimate the flow from Genale-Dawa river basin using a time series dataset of 16 years from 1990-2005. For calibration the model results in the performance criteria of R 2 = 0.903, and NSE = 0.8926, and D = -0.0002%, and for validation performance criteria of 2 R = 0.866, and NSE = 0.8447. Thus, HEC-HMS model has the ability to predict the water potential of the basin. Following the configuration, and application of HEC-ResSim model, the position of guide curve was fixed at a minimum operative level for GD-3 and assigned at top of conservation zone for GD-5, and GD-6 along with explicit system storage balance which is used to force the upstream reservoir, GD-3, to fill first, allowing the downstream reservoirs, GD-5, and GD-6 to stay empty as long as possible when operating for flood control. The results of annual average hydropower energy generated by the model from joint operation of the reservoirs system is 4,311.25 GWh/year. The whole cascade power generation increment is 381.25 GWh/year and it is a 9.701% improvement over the current design which is 3,930 GWh/year. Also, Combined reservoir system operation model is capable to store 517.13 million cubic meter flood water resources annually which shows 16.75% total reduction of spill release over the current design.

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Keywords

Arc-GIS, Arc-Hydro, HEC-GeoHMS, HEC-HMS, HEC-ResSim, Optimal Water Release, Storage Balance, Genale-Dawa River Basin

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