Hydraulic Roughness Coefficients as Affected by Random Roughness

Random roughness parameters are used to characterize surface microrelief. In this study, random roughness was determined following six selected tillage operations. Random roughness measurements agreed closely with values reported in the literature. Surface runoff on upland areas is analyzed using hydraulic roughness coefficients. Darcy-Weisbach and Manning hydraulic roughness coefficients were identified in this investigation on each soil surface where random roughness values were determined. Hydraulic roughness coefficients were obtained from measurements of discharge rat巳and flow velocity. The experimental data were used to derive regression relationships which related Darcy-Weisbach and Manning hydraulic roughness coefficients to random roughness and Reynolds number. Random roughness values available in the literature can be substituted into the regression equations to estimate hydraulic roughness coefficients for a wide range of tillage implements. The accurate prediction of hydraulic roughness coefficients will improve our ability to understand and properly model upland flow hydraulics