Rapid assessment of field erosion and sediment transport pathways in cultivated catchments after heavy rainfall events

摘要

This paper explores a scale-adapted erosion mapping method which aims at a rapid assessment of field erosion and sediment transport pathways in catchments up to several square kilometres and compares the results with the output of a well-known erosion model (LISEM). The mapping method is based on an event-defined classification scheme of erosion intensity (zero, weak, moderate and strong) that is applied to arable fields, in combination with incision measurements of erosion features for each erosion intensity class on a small sample of fields. Sediment deposition is classified on the basis of quantity indicators and abundance. In addition, relevant conditions and erosion factors are determined for each field.The method was applied to an agricultural catchment (4-2 km(2)) in the Sundgau (Alsace), after a short but violent thunderstorm in May 2001, to illustrate its potential use and its limitations. The rainfall event led to strong erosion on the arable fields and a muddy flow that caused significant damage in the built-up area. On the basis of the analyses of the incision measurements in combination with the mapping of erosion intensity classes, total erosion for the catchment was estimated as 15 000 t (an average of about 36 t/ha). Sediment deposition was found to occur in three major locations: (1) in thalwegs at the interface between maize and downslope winter wheat fields, (2) in downslope headlands where the flow direction suddenly changed due to oriented tillage structures in the perpendicular direction, and (3) the lowest corners of fields which collect all the runoff from the field. Preliminary data analyses suggest that erosion intensity is related to field size and/or tillage direction and to slope morphology. Model output (LISEM) appeared to depend more strongly on slope gradient than the results obtained with the mapping method.The method yields a database, which can be used as a foundation for conservation strategies in small regions with similar land use and geomorphology. The mapping and modelling methods are compared, and their complementary aspects are highlighted. Copyright (C) 2005 John Wiley Sons, Ltd.