Evaluating Manning's roughness coefficients for tilled soils

Abstract

A procedure for determining Manning's roughness coefficients from small field plots receiving simulated rainfall is presented. The procedure determines detention storage by hydrograph analysis and employs Manning's resistance equation to obtain effective Manning's roughness coefficients from field plots under different management practices. To validate the hydrograph analysis method, Manning's roughness coefficients and data of infiltration rate, obtained by the hydrograph analysis method, were used as inputs to the kinematic wave equation. Runoff hydrographs thus predicted, compared with observed runoff hydrographs, indicated that the hydrograph analysis method provides accurate determination of infiltration rate and of effective Manning's roughness coefficients; it also accounts for surface routing of runoff over small field plots.