Large sediment-retention dams, built in a cascade (a chain of check dams), can impose hazard (hyper-concentrated sediment flow, debris flow), if they fail during torrential flash floods or when destroyed by overtopping by a debris flow initiated on slopes or in natural torrential channels. Using estimates of specific annual sediment yields in torrential watersheds on one hand, one can use the area of the watershed and the storage volume of torrential check dams in order to estimate the maximum potential of sediment stored in the retention volume of the check dams—as a first approximation for the magnitude of the debris flows initiated by the dam failure. On the other hand, one can use debris-flow susceptibility maps to estimate likelihood for triggering of potential debris flows in torrential watersheds under investigation (we used debris-flow susceptibility map of Slovenia in the scale 1:250,000). A field study on the status of several tens of check dams in the Upper Sava River in NW Slovenia with regard to the question whether they should be taken as a possible debris-flow source was performed.