Characterization and modelling of the spatial heterogeneity of snowmelt erosion

Recent studies about soil erosion show that erosion rates in winter can reach or exceed erosion induced by summer events. A factor of particular importance is the incidence of frozen soil, which modifies the surface runoff generation and also the erodibility of the soil. In this paper, investigations are conducted to characterize the snowmelt erosion events in the 1·44 km 2 ‘Schafertal’ research catchment that is located c. 150 km southwest of Berlin. Two runoff events of different initial conditions are compared and analysed. Although the net erosion rate in the catchment is relatively low, the described event with soil frost is considerably different from the event without soil frost. For example, the net erosion, maximum and median suspended sediment concentrations are significantly higher for the event with frozen soil. The results presented suggest that the sediment source areas differ for both situations. On one hand the channel or sediment flushing is identified as the source, while on the other hand hill slope processes and intra-storm variations are recognized for the soil frost situation. A model modification is presented to improve the estimation of spatial differentiation of surface runoff within the continuous hydrological model WaSim, which is linked to the erosion model AGNPS. Based on measurements of topsoil temperature at locations with diverse exposition and land use, an algorithm is developed. The average agreement of air temperature to the calculated topsoil temperature is r 2 = 0·75. The spatial information about soil frost is utilized to modify the infiltration characteristics of the soil. Hence, the spatial aspects of runoff generation in winter conditions and the related transport of sediment is considered in a more realistic way. The spatial results of the modelling are plausible but the estimation of erosion needs further improvement. Copyright © 2005 John Wiley & Sons, Ltd.