An Assessment of Long-term Overtopping of Dam under Climate Change (A Case of Baro I and II Hydropower Project)
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Date
2019-10
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Addis Ababa University
Abstract
Current climate change is occurring in the world in serious cases, which affects all living and non- living things. Climate change will cause the problem of flooding, which damages the constructed structures (dam, road, buildings, bridge, etc.). This study assesses dam overtopping in case of Baro I and II under climate change on future projection representative concentration pathway (RCP) scenario RCP4.5 and RCP8.5 by using Regional Climate Model (RCM) and hydrological model by Arc SWAT model. The RCM data obtained from the Coordinated Regional Downscaling Experiment (CORDEX) Africa project using the driving force of General Circulation Model (GCM) of two institutions (MPI and CCLM). The downscaled RCM output bias-corrected by distribution mapping method and evaluated by the coefficient of determination (R2), NSE (Nash Sutcliffe Efficiency (NSE) and Percent of Bias (PBIAS) results in 0.988, 0.969, and 6.485, respectively. The input data used for the model meteorological data, digital elevation model (DEM), land use land cover map 2018, and soil. The sensitivity analysis, calibration, and validation of the model is done by using SWAT-CUP model by using SUFI2 method. The model performance was evaluated using the coefficient of determination (R2) and Nash-Sutcliffe Efficiency (NSE) results for calibration of the value of 0.75 and 0.71 respectively, for validation 0.84 and 0.82 respectively on a monthly basis.
Inflow hydrograph developed by Hershfield method and reservoir routing was done. The result obtained for two scenarios (rcp4.5 and rcp8.5) Baro I present future of peak inflow flow 3783.2 m3/s and 5314.6 m3/s, outflow 2244.9 m3/s and 3004.9 m3/s, mid future peak inflow 3892.9 m3/s and 3314.6 m3/s, outflow 2299.0 m3/s and 2430.8 m3/s and far future of peak inflow 3177.36 m3/s and 3207.27 m3/s, outflow 1903.01 m3/s and 1918.68 m3/s respectively. The result obtained for two scenarios (rcp4.5 and rcp8.5) Baro II present future of peak inflow flow 2233.5m3/s and 2428.6 m3/s, outflow 2081.4 m3/s, and 2294.5 m3/s, mid future peak inflow 3286.0 m3/s and 3057.0 m3/s, outflow 2871.4 m3/s and 2544.19 m3/s and far future of peak inflow 1882.85 m3/s and 1898.42 m3/s, outflow 1707.97 m3/s and 1663.47 m3/s respectively.
After frequency analysis, the simulated out of the RCM data result for two scenarios (rcp4.5 and rcp8.5) present future 6483.6 m3/s and 6110.5m3/s, mid future 5364.5m3/s and 6304.7m3/s, far future 5134.8 m3/s and 4918.2m3/s respectively.
Generally, the outflow above the projected RCM output for two scenarios (RCP4.5 and RCP8.5) result shown next future the spillway would not pass it. Hence, the dam at Baro I and II would be overtopped next future period.
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Keywords
Baro-Akobo, dam, overtopping, climate change, spillway, RCM, Arc SWAT