Application of Integrated Modeling Framework for Managing Downstream Flood Risk in Hydropower Dams under Inflow Uncertainty

Effective reservoir planning and management are critical components in hydrology and water resource management. However, adopting appropriate operation policies after satisfying the downstream hydraulic requirements still needs to be explored. The potential of downstream flooding influenced by uncertainties of the inflow to the reservoir can impede the decision-making strategies of the dam operators, affecting the dam regulation. In this work, we have applied a coupled reservoir operation and hydrodynamic (CRO-Hydro) model for assessing the downstream flood risk under inflow uncertainty. The two models were coupled using a feedback system based on the output of one model. The system utilized downstream flood level data from the hydrodynamic part of the model to trigger the reservoir operation model. This enabled the reservoir to initiate an advance release by discharging water before the occurrence of the flood. Our approach quantifies the advance release using a simulation-optimization model to minimize downstream flood levels while maintaining an acceptable power production efficiency under perfect forecast conditions. A sensitivity analysis of inflow uncertainty, considering the peak flow and time of arrival of peak flow, was conducted to check the downstream flood risk. We demonstrate our methodology in the Ranganadi Hydro Electric Project located in Arunachal Pradesh, India. Results showed that under a perfect forecast, CRO-Hydro successfully lowered the flood levels to keep them below the danger level in the downstream flood-prone section. The sensitivity analysis revealed that the risk is higher with the early arrival of the flood peak compared to the late arrival of the expected flood. Even with a lag of 6 h, the power production efficiency has remained consistently above 85%. Thus, the inflow forecast should prioritize predicting peak flow and the early arrival time for decision-making by dam authorities.