Bankfull regional curves that relate channel dimensions and discharge to watershed drainage area are useful tools for assisting in the correct identification of bankfull elevation and in stream restoration and reconstruction. This study assessed 28 stable streams located in two physiographic regions of Kentucky: the Inner Bluegrass and the Outer Bluegrass. Bankfull channel dimensions, discharge, and return period as well as average channel slope, median bed material size, sinuosity, Rosgen stream classification, and percent impervious area were determined. Significant relationships were found between drainage area and the bankfull characteristics of cross-sectional area, width, mean depth, and discharge for both the Inner Bluegrass and Outer Bluegrass regions (a = 0.05). It was also found that the percent impervious area in a watershed had minimal effect on bankfull dimensions, which is attributed to the well-vegetated nature of the streambanks, cohesive streambank materials, and bedrock control. No significant differences between any of the Inner Bluegrass and Outer Bluegrass regional curves were found (a = 0.05). Comparisons were made between the Inner Bluegrass and Outer Bluegrass curves and others developed in karst-influenced areas in the Eastern United States. Although few significant differences were found between the regional curves for bankfull discharge and width, a number of the curves differed with regards to bankfull cross-sectional area and mean depth.

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 OPEN ACCESS Water 2011, 3 924 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 m 3 s −1 and wider and shallower at bankfull discharges greater than 20 m 3 s −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.