HYDRAULIC GEOMETRY RELATIONSHIPS AND REGIONAL CURVES FOR THE INNER AND OUTER BLUEGRASS REGIONS OF KENTUCKY

Hydraulic geometry relationships and regional curves are used in natural channel design to assist engineers, biologists, and fluvial geomorphologists in the efforts undertaken to ameliorate previous activities that have diminished, impaired or destroyed the structure and function of stream systems. Bankfull channel characteristics were assessed for 14 United States Geological Survey (USGS) gaged sites in the Inner Bluegrass and 15 USGS gaged sites in the Outer Bluegrass Regions of Kentucky. Hydraulic geometry relationships and regional curves were developed for the aforementioned regions. Analysis of the regression relationships showed that bankfull discharge is a good explanatory variable for bankfull parameters such as area, width and depth. The hydraulic geometry relationships developed produced high R2 values up to 0.95. The relationships were also compared to other studies and show strong relationships to both theoretical and empirical data. Regional curves, relating drainage area to bankfull parameters, were developed and show that drainage area is a good explanatory variable for bankfull parameters. R2 values for the regional curves were as high as 0.98

Bankfull Hydraulic Geometry Relationships for the Inner and Outer Bluegrass Regions of Kentucky

Bankfull hydraulic geometry relationships relate bankfull stream dimensions, such as cross-sectional area, width, mean depth, mean velocity, width to depth ratio, and slope to bankfull discharge. These relationships can assist in determining a design discharge for stream restoration and management projects. This study assessed 27 stable streams located in the Inner Bluegrass and Outer Bluegrass regions of Kentucky. Reaches were selected based on the presence of a U.S. Geological Survey gage, as well as other conditions such as presence of readily identifiable bankfull indicators, stability indices, and site accessibility. Bankfull channel dimensions and discharges were determined, and hydraulic geometry relationships were developed for both the Inner Bluegrass and Outer Bluegrass regions. These scaling relationships for karst-influenced streams were similar to others reported in the literature for non-karst areas. Significant differences between the regions were found only for bankfull width and width-to-depth ratio. Streams in the Inner Bluegrass tended to be more narrow and deep at bankfull discharges less than 10 m3s−1 and wider and shallower at bankfull discharges greater than 20 m3s−1 as compared to stream in the Outer Bluegrass. It is suspected that physiographic conditions related to local geology and/or riparian vegetation at three sites in the Outer Bluegrass accounted for these differences. Results of this study indicate that in instances of geologic variation within a physiographic region, hydraulic geometry relationships may require evaluation at the watershed scale