Suitability of HEC-RAS for Flood Forecasting

At present, most river flood forecasts are conducted using a two-step procedure. First, flood routing is conducted, normally using hydrological models. The resulting flood peaks are then converted to water level forecasts using a steady flow hydraulic model, such as HEC-RAS. Recently, the HEC-RAS model has been extended to facilitate unsteady flow analyses, and while the numerical scheme is not robust enough to handle dynamic events (such as ice jam release floods) or supercritical flows, it does have the capability to route simple open water floods and produce water level forecasts at the same time. Here, the viability of the HEC-RAS unsteady flow routine for flood forecasting is examined through an application to the Peace River in Alberta and it is shown that accuracy comparable to more sophisticated hydraulic models can be achieved. Since many agencies already have HEC-RAS models established for floodplain delineation purposes, it would be a simple matter to extend them to the flood forecasting application. An ancillary advantage would be that flood forecasting accuracy could potentially be improved and simplified into a one-step process, without necessitating a time-consuming transition to unfamiliar models.