VOL. 38, NO. 3

JUNE 2002

Analysis of Hydraulic Geometry Relationships for Urban Streams throughout the Piedmont of North Carolina

Barbara A. Doll, Dani E. Wise-Frederick, Carolyn M. Buckner2, Shawn D. Wilkerson3,
William A. Harman2, and Rachel E. Smith2

Abstract: Hydraulic geometry relationships, or regional curves, relate bankfull stream channel dimensions to watershed drainage area. Hydraulic geometry relationships for streams throughout North Carolina vary with hydrology, soils, and extent of development within a watershed. An urban curve that is the focus of this study shows the bankfull features of streams in urban and suburban watersheds throughout the North Carolina Piedmont. Seventeen streams were surveyed in watersheds that had greater than ten percent impervious cover. The watersheds had been developed long enough for the streams to redevelop bankfull features, and they had no major impoundments. The drainage areas for the streams ranged from 0.4 to 110.3 square kilometers. Cross-sectional and longitudinal surveys were conducted to determine the channel dimension, pattern and profile of each stream and power functions were fitted to the data. Comparisons were made with regional curves developed previously for the rural Piedmont, and enlargement ratios were produced. These enlargement ratios indicated a substantial increase in the hydraulic geometry for the urban streams in comparison to the rural streams. A comparison of flood frequency indicates a slight decrease in the bankfull discharge return interval for the gaged urban streams as compared to the gaged rural streams. The study data were collected by North Carolina State University (NCSU), The University of North Carolina at Charlotte (UNC), and the Charlotte Stormwater Service. Urban regional curves are useful tools for applying natural channel design in developed watersheds. They do not, however, replace the need for field calibration and verification of bankfull stream channel dimensions.

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