Development of regional flood-duration–frequency curves based on the index-flood method

The aim of this research paper is to develop a statistical model that provides a more complete description of a basinʹs flood regime. The approach adopted in this paper is based on the flood-duration–frequency (QdF) analysis which takes into account the temporal variability of floods. This approach is analogous to the intensity-duration–frequency (IdF) model commonly used for rainfall analysis. The proposed model allows QdF curves for a given basin to be estimated while using a minimum number of parameters. This model is called ‘converging’ model because of the observed convergence of distributions towards small return periods. A local (at-site) model and a regional approach are developed. The regional approach uses classical concepts of regional hydrologic frequency analysis (index-flood (IF) method) and can be used for basins where no streamflow data is available. Results from 158 catchments located in the provinces of Quebec and Ontario (Canada) are used to illustrate the method.