Bankfull characteristics of Ohio streams and their relation to peak streamflows

Abstract

Regional curves, simple-regression equations, and multiple-regression equations were developed to estimate bankfull width, mean bankfull depth, bankfull cross-sectional area, and bankfull discharge of rural, unregulated streams in Ohio. The methods are based on geomorphic, basin, and flood-frequency data collected at 50 study sites located on unregulated natural alluvial streams in Ohio, of which 40 sites are located near streamflow-gaging stations. The regional curves and simple-regression equations relate the bankfull characteristics to drainage area. The multiple-regression equations relate the bankfull characteristics to drainage area, main-channel slope, main-channel elevation index, median bed-material particle size, bankfull cross-sectional area, and local-channel slope. Average standard errors of prediction for bankfull width equations range from 20.6 to 24.8 percent, mean bankfull depth equations range from 18.8 to 20.6 percent, bankfull cross-sectional area equations range from 25.4 to 30.6 percent, and bankfull discharge equations range from 27.0 to 78.7 percent. Field surveys were conducted at each of the 50 study sites to collect the geomorphic data. Bankfull indicators were identified and evaluated, cross-section and longitudinal profiles were surveyed, and bed- and bank-material were sampled. Field data were analyzed to determine various geomorphic characteristics, such as bankfull width, mean bankfull depth, bankfull cross-sectional area, bankfull discharge, streambed slope, and bed- and bank-particle size distribution. Various geomorphic characteristics were analyzed using a combination of graphical and statistical techniques. Simple-regression equations were developed to estimate 2-, 5-, 10-, 25-, 50-, and 100-year flood-peak discharges of rural, unregulated streams in Ohio from bankfull cross-sectional area. The average standard errors of prediction are 31.6, 32.6, 35.9, 41.5, 46.2, and 51.2 percent, respectively. The logarithms of the annual peak discharges for 40 gaged study sites were fit by a Pearson Type III frequency distribution to develop a flood-peak-frequency relation for each site. The peak-frequency data were related to geomorphic, basin, and climatic variables by multiple-regression analysis. The study and methods developed are intended to improve the understanding of the relations between geomorphic, basin, and flood characteristics of streams in Ohio and to aid in the design of hydraulic structures, such as culverts and bridges, where stability of the stream and structure is an important element of the design criteria.