Characterization of rainfall - microrelief interactions with runoff using parameters derived from digital elevation models (DEMs)

The main objective of this study was to investigate how the interactions between rainfall energy and microrelief affect soil surface sealing and runoff. Furthermore, several roughness indices and geostatistical procedures were tested for their ability to characterize microrelief.Runoff boxes filled with soil from the plough layer of a silty Luvisol were subjected to simulated rainfall. Two types of microrelief (rough and fine) were tested at two rainfall intensities (30 and 60 mm/h). A photogrammetric technique was used to develop digital elevation models (DEMs) of the soil surface before and after rainfall with a resolution in height of 0.2 mm and a grid spacing of 2 mm.The random roughness coefficient according to Currence & Lovely (1970) was found to be sensitive to surface microrelief variations. Semivariograms of the data indicated that big clods were the main elements determining microrelief and the ratio of total surface are to map area. The observed variations in runoff as a function of microrelief were best explained by rainfall energy per total surface area and by the relative contribution of the effective normal component of kinetic energy with respect to the impact angle of raindrops. Microdepression storage was only 0.6 mm or less and was found to be negligible in terms of runoff.