Even more destructive: cascade dam break floods

The present work aims to bridge the gap of knowledge of how and to what extent a cascade dam break flood is distinguished from a single dam break flood over both fixed and mobile beds. A shallow water hydrodynamic model is deployed to resolve the floods because of successive and synchronous break of two cascade dams. A cascade dam break flood features a substantially raised peak stage, advanced timing, or both, at a downstream station as compared with that because of a single dam break irrespective of whether the impacts of sediment transport and bed evolution are considered or not. The dam‐to‐dam spacing and relative dam height in the case of successive break (or initial reservoir water depth in the case of synchronous break) play a central role in dictating the flood, and based on these variables, the threshold conditions for peak‐stage rise are evaluated. The present finding characterises a higher risk of flooding from a cascade dam break than a single dam break, which should be accounted for in flood defence design and alleviation schemes.