MODELING SOIL-EROSION BY OVERLAND-FLOW - APPLICATION OVER A RANGE OF HYDRAULIC CONDITIONS

Modeling the erosion of cohesive soils on slopes where shallow overland flow is dominant requires practical and useable equations that rely upon key parameters: F, the fraction of excess stream power available for mechanical work, and, J, the specific energy of entrainment. Data from a series of rainfall simulator experiments were used to evaluate the consistency of F and J for two contrasting soil types across a range of hydraulic conditions. A summary of the conceptual model together with key equations used in the analyses of data is given. Parameter evaluation and the implications of using inappropriate sediment concentrations and/or assuming spatially uniform flow when rills are present are discussed. The two soils studied were a cracking clay (vertisol) and a slightly dispersive sandy clay loam (aridisol). From detailed information on rill dimensions and frequency, calculated values of F were found to be relatively insensitive to changes in hydraulic conditions for turbulent flow conditions. Its value was approximately 0.1 for both soil types. Parameter J was also reasonably consistent when rill dimensions and frequency were used in the analyses. The F and J values were more scattered by assuming spatially uniform flow across a surface when rills were present.