Environmental role and cartographic identification of waterlogged soils of bottom lands

Abstract

Environmental role of waterlogged areas of bottom land is related to three processes: interception of run-off waters contaminated by pesticides, heavy metals and suspended matter, adsorption on soil components of some of these pollutants and denitrification. In intensive farming zones, these waterlogged areas of bottom land do not play any longer their environmental functions. On the contrary, they can be a source of environmental risk for the channel network. Consequently, an important part of agro-environmental policy concerns these waterlogged areas of bottom land whose extent is about 20% of Brittany territory. The first step of agro-environmental policy is the cartographic identification of these areas. In this project, the cartographic identification has been performed using Digital Elevation Models. A 20m grid DEM produced by stereo-restitution of SPOT images was used. A topographic index derived from Beven-Kirkby index was used to identify these waterlogged areas of bottom land. Drainage network was also modelised with use of DEM. Watersheds boundaries, sub-watersheds boundaries and sloppy areas were also produced with DEM modeling.