1 Scientific registration n° : 458 Symposium n° : 31 Presentation : oral Soil Erosion on Upland Areas under Different Hydrologic Regimes and Soil Surface Conditions Erosion des sols de versants sous différents régimes hydrologiques et conditions de surface du sol RÖMKENS Mat J. M. (1), HELMING Katharina (2), PRASAD Shyam N. (3) (1) USDA-ARS National Sedimentation Lab., P.O. Box 1157, Oxford, MS, 38655 USA (2) ZALF, Eberswalder Str. 84, D-15374 Muencheberg, Germany (3) University of Mississippi, University, MS 38677 USA INTRODUCTION Soil erosion processes are multifaceted and interrelated processes involving a host of factors and conditions, which combinations, variations, and interactions substantially affect the observed soil loss. Prediction of soil erosion is largely based on measurements of soil loss from natural runoff or rainulator plots, covering a spectrum of soils, topographic conditions, and management practices. The most notable example of prediction technology has been the development of the Universal Soil Loss Equation or USLE (Wischmeier and Smith, 1978), which recently was upgraded to the Revised Universal Soil Loss Equation (RUSLE) (Renard et al., 1997). To improve the reliability, generality, and accuracy of erosion prediction, the development of process based models and relationships is of paramount importance. While these models are often realisations and formulations of conceptional notions of the developer(s), the complexity of real situations requires that additional and realistic experimental efforts be made to obtain a better insight of the interacting role of many of the factors that are involved. A particular aspect that is of interest to erosion specialists and for which current soil erosion prediction technology is inadequate, is the role of surface roughness in soil erosion processes. The conventional wisdom has been to assume that surface roughness increases the surface storage capacity of rain and reduces the flow velocity and thus erosive power of runoff (Zobeck and Onstad, 1987). On the other hand, on rough surfaces flow concentrates and the potential for scouring action increases (Helming et al., 1998). The relative significance of these processes is further confounded by the rainfall intensity regime, surface seal development and breakdown, as well as the subsurface soil and soil water conditions (Römkens et al., 1997). This paper highlights recent research activities which examine the respective role of these interacting processes as they affect soil erosion.