Understanding the equivalent relationship of the flood control storage between Cascade Reservoirs

Abstract

Joint flood control operations in cascade reservoirs are critical for mitigating flood disasters. To explore the full potential of flood control in cascade reservoirs, it is necessary to find the equivalent relationship among the cascade reservoirs. After defining the concepts of equivalent flood control storage and the equivalent ratio, its general equivalent relationship has been derived for the downmost reservoir regardless of its flood regional composition and upstream reservoirs operation rules. The cascade reservoirs in the upstream of the Changjiang River and the Three Gorges Reservoir are taken as our case study. Driven by the six design floods, the impacts of flood magnitude, hydrograph, and the amount of the occupied upstream flood storage on the equivalent ratio of the Three Gorges Reservoir have been figured out. The results show that the equivalent ratio increases with flood magnitude. If the main part of the peak of the flow at the downmost reservoir is from the regional flow, and the flood peak at the interval region is part of the first half of the downstream flood peak, the equivalent ratio is approaching 0. The impact of the amount of occupied upstream flood storage on the equivalent ratio is found to be dependent on the magnitude and hydrograph of the inflow into the downmost reservoir. © 2026 American Water Resources Association.