DRAFT

Soil surface aggregates (random roughness) and ridges (oriented roughness) can reduce soil loss by wind erosion. The soil roughness factor (K’) is used to describe the effect of soil roughness on soil loss by wind. The K ’ in the Wind Erosion Equation (WEQ) model is a ridge roughness value which does not include the random roughness effect and is not modified by rainfall. This study was conducted to develop a soil roughness factor for the Revised Wind Erosion Equation (RWEQ) model. Wind tunnel data was used to generate the roughness factor which included both aggregate (random) and ridge (oriented) roughness. Surface roughness decay functions were used to predict K ’ (ridge and aggregate levels) after each rainfall event using rainfall amount and storm erosivity index (EI). A function was used to predict K ’ parallel and perpendicular to the wind for ridged fields. The soil surface roughness measurement obtained from the chain method and ridge height and spacing can be used to estimate K’. A look-up table was developed to obtain K ’ based on soil surface roughness measurements