How Surface Mounds and Depressions Change During Rainfall Events.

The soil  roughness, or microrelief, controls processes occurring on the surface.  Although there are numerous studies on how soil roughness affects soil erosion processes, little are focused on quantifying different roughness functions on surface hydrology and erosion, i.e., water diverging and soil eroding from surface mounds and water converging and sediment depositing in surface depressions.  The objective of this study was to measure the changes in surface depressions and mounds during rainfall events and to analysis how different surface forms affect  runoff and sediment delivery.  Rainfall simulation experiments were carried out on a soil box 1.2 m long by 0.6 m wide at 10% slope.   The soil was collected from the surface horizon of a Crosby-Miami complex alfisol with 20% clay, 66% silt and 14% sand. Four rainfall events with increasing intensity and total 120 mm of rainfall were applied to each rough surface (mound vs. depression). A laser scanner was used to measure microrelief and the digital elevation models (DEMs) before and after rainfall were analyzed for changes in surface elevation.  The sizes (volumes) of mounds and depressions were decreased significantly after rainfall, but to different extents. The mean volume of mound was reduced by 33.18 cm³. The mean volume of depression was reduced by 246.69 cm³. In terms of elevation changes at the highest and lowest points of the mounds and depressions, the average decrease for the mounds is 10.3 mm and the average increase for the depressions is 15.1 mm.  These differences in micro-scale morphological changes for mounds and depressions indicate that surface depressions trapped sediments generated from the mounds.  By analyzing how surface mounds and depressions evolve during rainfall events provides a mechanistic understanding on how soil roughness affects runoff and sediment production.