Roughness Coefficients for Selected Residue Materials

Analysis of surface runoff on upland areas requires identification of roughness coefficients. A laboratory study is conducted to measure Darcy-Weisbach and Manning roughness coefficients for corn, cotton, peanut, pine needles, sorghum, soybeans, sunflower, and wheat residue. Varying rates of flow are introduced into a flume in which selected amounts of residue are securely attached. Roughness coefficients are calculated from measurements of discharge rate and flow velocity. The laboratory data are used to derive regression equations for relating roughness coefficients to Reynolds number and either percent residue cover or residue rate. Separate equations are developed for Reynolds number values from 500 to 20,000, and from 20,000 to 110,000. Generalized equations are presented for estimating roughness coefficients for other residue materials not used in this investigation. Accurate prediction of roughness coefficients for residue materials will improve our ability to understand and properly model upland flow hydraulics