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 interactio ns 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 Luviso l were subjected to simulated rainfall. Two types of microrelief (roug h and fine) were tested at two rainfall intensities (30 and 60 mm/h). A photogrammetric technique was used to develop digital elevation mode ls (DEMs) of the soil surface before and after rainfall with a resolut ion in height of 0.2 mm and a grid spacing of 2 mm. The random roughne ss coefficient according to Currence & Lovely (1970) was found to be s ensitive to surface microrelief variations. Semivariograms of the data indicated that big clods were the main elements determining microreli ef and the ratio of total surface are to map area. The observed variat ions in runoff as a function of microrelief were best explained by rai nfall energy per total surface area and by the relative contribution o f 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.