REGIONALIZATION OF CATCHMENTS FOR REGIONAL FLOOD FREQUENCY ANALYSIS

An approach to catchment regionalization is presented, in which an agglomerative hierarchical clustering algorithm used to define homogeneous regions that can be used for regional flood frequency analysis. Catchment similarity is expressed using seasonality measures derived from the mean date of occurrence of the annual maximum flood and its associated dispersion. Regions that are largely geographically contiguous are obtained by incorporating. a distance measure into the similarity metric used within the clustering algorithm. The initial regions formed using the clustering algorithm are subsequently modified in an attempt to enhance the overall regional homogeneity. The approach is demonstrated through an application to a set of 217 catchments from the Saskatchewan-Nelson River basin in west-central Canada.