Résumé
This project led to the development of a method in order to assess the surface water contamination potential by pesticides at the small watershed scale. This method considers both spatial and temporal dimensions. The central idea is to aggregate at the catchment scale water and pesticides fluxes simulated at the plot scale, taking into account landscape elements influence (roads, ditches, embankments, buffer zones) on the transferred flux. The goal is to elaborate statistical descriptors of contamination at the outlet. Each catchment component is treated as a typical element, according to its characteristics (soil, slope, land use, agricultural practices ... ), which limits the number of local scale simulations and will facilitate the transposition to larger watersheds (several tens of square kilometers). This approach profits on the knowledge that we have of the processes governing the fate pesticides at plot level or within the landscape features, without having the complexity of a “complete” pesticides transfer model at the catchment scale. The work was carried out on two small catchments where data are numerous but of different quality. They highlighted the need to carefully define the parameters set for the MACRO model, which was used at the plot level. When possible, data should be site specific. A tool making it possible to simulate a large number of simulations was developed. It was applied in order to study the factors which govern pesticides transfers in MACRO for each situation. A method which delineates the catchment in areal or linear homogeneous elements was developed. On top of that, it defines hydrological connections between these elements, which makes it possible to identify which plots are connected or on the contrary isolated from the hydrographic network. Thus a first diagnosis of vulnerability at the catchment scale is possible. Finally, a catchment scale aggregation method of locally simulated water and pesticides fluxes was developed. An analysis method, based on data warehouses, was developed, which makes it possible to perform a thorough analysis of the simulation results. The aggregation method still has to be validated and then applied to a large set of scenarios. Anyway, it will finally allow to qualify more soundly the risk of contamination at the catchment scale, and to identify the most contributive areas or the most problematic configurations.