A Relook at Ohio Watershed Regions for Homogeneity in Flood Frequency Analysis

Regionalization approaches are widely used in hydrology to identify homogeneous groups (regions) of watersheds to facilitate prediction of hydro-meteorological extreme events in ungauged basins for various applications. This paper evaluates statistical homogeneity of watersheds in each of the regions of Ohio that were delineated in the past studies (Koltun, 2003; Koltun and Roberts, 1990) to arrive at regression relationships for estimating flood-peak discharges at rural and unregulated streams. Results based on L-moment homogeneity tests indicated that all the Ohio regions are heterogeneous. Consequently a new set of homogeneous regions are proposed in Ohio based on conventional and global fuzzy cluster analysis procedures. Regional growth curves are developed for each of the newly formed regions and it is shown that their use results in effective quantile estimates at ungauged sites in watersheds of Ohio when compared with those resulting from the use of regression relationships that are being used for quantile estimation by United States Geological Survey (USGS).