Dernierement, le modele HEC-RAS a ete etendu afin de faciliter les analyses d'ecoulements non permanents. Les debits de pointe de crue qui en resultent sont ensuite convertis en des previsions de niveau d'eau a l'aide d'un modele hydraulique a ecoulement permanent, tel que le HECRAS. Tout d'abord, un calcul de la propagation des crues est effectue, normalement a l'aide de modeles hydrologiques. Resume : A l'heure actuelle, la plupart des previsions de crues des rivieres sont faites au moyen d'une methode en deux etapes. 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. 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.
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. 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. The resulting flood peaks are then converted to water level forecasts using a steady flow hydraulic model, such as HEC-RAS. First, flood routing is conducted, normally using hydrological models. Abstract: At present, most river flood forecasts are conducted using a two-step procedure.