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.