Bankfull Regional Curves for the Inner and Outer Bluegrass Regions of Kentucky

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 (α=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 (α=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.