REGIONAL FLOOD FREQUENCY WITH HIERARCHICAL REGION OF INFLUENCE

Regional flood frequency analysis involves combining extreme-flow info rmation from numerous stations to enhance the reliability of the tempo ral characterization of extreme-how data at sites with short periods o f record. The region of influence (ROI) approach used herein, defines regions such that each site has a potentially unique combination of st ations. The similarity of the selected stations is ensured by incorpor ating a homogeneity test into the regionalization process. A hierarchi cal feature is added to the ROI approach to further enhance the effici ency of the spatial information transfer. This is done by taking advan tage of the different spatial similarity scales that have been observe d for different orders of moments for a flood frequency distribution. The incorporation of this concept into the ROI framework results in a set of ROIs for a site as opposed to a single ROI. The hierarchical RO I approach is evaluated through the use of a Monte Carlo experiment ap plied to data representative of a collection of unregulated catchments in the midwest portion of Canada. The simulation experiment shows tha t an improvement in flood quantile estimation is achieved.