A continuous simulation model for design-hydrograph estimation in small and ungauged watersheds

The estimation of design hydrographs for small and ungauged watersheds is a key topic in hydrology. In this context, event-based procedures, which transform design storms deduced from intensity-duration-frequency curves by lumped rainfall-runoff models, are commonly applied. This study introduces a continuous simulation model that involves a two-stage rainfall generator, a geomorphological rainfall-runoff model and a flood frequency analysis applied to simulated runoff time series. The resulting design hydrograph with an assigned return period preserves peak and volume information. The case study results indicate that the continuous model is able to return a range of flood scenarios corresponding to a wide range of possible watershed physical conditions. Moreover, the rainfall-runoff model applied using empirical calibration without observations appears to be as accurate as other models based on regionalized information.