Overland flow on disturbed soil

A field experiment was conducted to investigate aspects of the erodible boundary of tilled soils under simulated rainfall; surface roughness storage and hydraulic resistance of overland flow. Experimental plots, with four types of tillage implemented roughness, were equipped with piezometer sets buried under the surface to measure hydrostatic pressure and a system of flow tracers composed of floating objects, border markings and clocks as spatial and temporal references of the surface process, and video cameras to record the rainfall-runoff process.The storage volume of surface roughness was evaluated using coefficient of storage or the degree to which hydrostatic pressure increased on the tilled layer during the process. Three physically based models were developed to predict time responses of depression and detention storage, and ponding using rainfall rate, porosity, initial moisture content and coefficient of storage.The overland flow resistance of surface roughness was investigated using a roughness index. The surface roughness index was determined as a unit hydraulic radius using spectral analysis to define surface geometry and hydraulic concepts of the boundary layer. Three commonly used resistance coefficients: Darcy-Weisbach friction factor, Manning roughness and Chezy resistance factor were evaluated for rill and interrill areas separately. Hydraulic roughness in interrill areas is generally greater than in constricted rill flow because the roughness in rills became inundated more quickly than interrill areas. During the rainfall-runoff event, the surface became smoother from the action of raindrops and flow erosion. However, as the event continued, surface roughness increased in some cases.On deformable boundaries of tilled soils, resistance is a function of the state of boundary roughness and flow. A physical relationship was developed to relate friction factor to the ratio of boundary shear velocity to flow velocity, degree of surface roughness inundation and degree of flow defect. This relation was found to be statistically satisfactory for the field data.U of I OnlyETDs are only available to UIUC Users without author permissio