Travail de fin d'études: Characterization of the spatial distribution of deposition in a small agricultural catchment. Comparison of a modeling approach using WaTEM/SEDEM with remote-sensing techniques (difference of DEMs)

Abstract

The new Common Agricultural Policy (CAP) has led to a new definition of the fields sensitivity to soil erosion. It revived the debates between scientists, farmers, and policy makers. Different methods and models exist to study erosion, but soil scientists point out a lack of data to study the spatial distribution of this phenomenon. This study focuses on an agricultural catchment of central Belgium in the Loess belt. We compared the model WaTEM/SEDEM (WS) enabling to model the spatial distribution of erosion and deposition at a catchment level to the difference of Digital Elevation Model (DEM) method. In this method, two DEMs, acquired at different periods, are subtracted from each other to spot the zones experiencing deposition (positive difference) and the eroded zones (negative difference). Different DEM data sources are exploited: Digital Terrain Model (DTM), Digital Surface Model (DSM), from Lidar and photogrammetry on a temporal scale of one decade. The results show that deposition modeled with WS is concentrated in the rills. The lidar DTMs, which seem the most reliable to study this phenomenon confirm this tendency, with a proportion of deposition 40% higher in the rills than in the inter-rills. In parallel, we carried out a statistical analysis of the maps of DEM differences to identify the variables influencing the spatial distribution of erosion and deposition. Our results show that it is possible to predict the elevation differences based on a model including variables that involve topography, climate and agricultural practices. Taking into account the uncertainty and the influence of vegetation, DTM and DSM show encouraging results in their usability to study erosion over one decade.