Quantifying Flood Frequency Modification Caused by Multi-Reservoir Regulation

The construction and the operation of multi-reservoir has severely altered the downstream design flood. This paper quantified the flood frequency modifications caused by multi-reservoir regulation with recorded data and a numerical model composed of peaks-over-threshold (POT) samples and time-trend models. The whole research was carried out in Dongjiang River Basin, Southern China. Results showed that (1) Sampling with the POT method could eliminate fake changes in change detection and prevent the underestimation of the design floods with an exceeding probability over 90% and the overestimation of the design floods with an exceeding probability less than 80%; (2) Multi-reservoir regulation severely reduced design flood when the exceeding probability was greater than 1% and smaller than 95%. The 10-year floods were mitigated the most. However, when the exceeding probability was over 95%, the impact was insignificant; (3) Flood mitigation was positively correlated to the number of reservoirs, but negatively correlated to the distance between the affecting reservoir and the affected station. However, when multiple reservoirs took effect on the design flood in one station, the closest reservoir did not necessarily take the most effect. The results of this research will amplify the theoretical basis for flood protection and the planning of regulation.