Hydrologic regionalization of watersheds in Turkey

Hydrologic regionalization can be employed for importing data from gauged sites to ungauged sites. A number of techniques have been developed for hydrologic regionalization. This study presents an approach that combines three regionalization techniques in order to obtain homogeneous regions and compute streamflow at desired ungauged sites. First, an agglomerative hierarchical clustering algorithm is used to determine the number of homogeneous regions. Second, homogeneous regions are defined by the k-means partitioning method. Third, the flow duration curve (FDC) method is used to compute streamflow discharge at desired ungauged sites in homogeneous regions. The combined approach was then applied to 26 river basins in Turkey having 1,410 river gauging stations, where homogeneous regions were identified and streamflow discharge was calculated at ungauged sites. At many of the unguaged sites, small hydropower projects are being planned for development. It was found that these 1,410 river gauging stations (26 river basins) can be grouped into six homogeneous regions. Homogeneous regions were found to be better distributed in the nonhierarchical k-means method than in the hierarchical method. FDCs, constructed for each homogeneous region, fit monthly discharge data with correlation coefficients between 95 and 100% for 85.7% of the gauging stations, between 85 and 94% for 12.5% of the stations, and between 72 and 84% for 1.8% of the stations.