Spring flood analysis using the flood‐duration–frequency approach: application to the provinces of Quebec and Ontario, Canada

Most often, flood frequency analysis describes a flood event only by its peak. However, the true flood severity is also defined by its volume and duration. This paper presents an approach allowing flood events to be considered in a more complete way: the flood‐duration–frequency (QdF) approach. In a similar manner to the rainfall intensity–duration–frequency analysis, averaged discharges are computed over differentfixeddurationsd. For each duration a frequency distribution of maximum averaged discharges is studied. Finally, a continuous formulation is fitted, as a function of the return periodTand the durationdover which discharges have been averaged. The proposed model has been tested for 169 catchments in the provinces of Quebec and Ontario, Canada. The shapes of the QdF curves enabled us to define different types of flood behaviour and to identify the corresponding geographic regions. This mapping of flood behaviour was the basis for the delineation of seven homogeneous geographical regions, containing catchments having the same hydrological behaviour as is required for regional flood frequency analysis.