Projet QualVados : Evaluation des mesures prises pour réduire les incidences de la pollution diffuse d’origine agricole et domestique sur la qualité des masses d’eau de surface et souterraines de la Région wallonne à l’aide du modèle EPICgrid

Wallonia (Southern Region of Belgium) implemented the Nitrates Directive through a first actions plan in 2002 followed by a second action plan in 2007. It designated vulnerable zones and introduced various mandatory practices in order to reduce the nitrate contamination risk. . In Wallonia, nitrate-related problems are obvious in several groundwater bodies and their trends over the past 30 years are worrying. The main part of the contamination level is due to agricultural diffuse pollution. Nevertheless, some pollution peaks are observed mainly coming from domestic sewage. In order to assess the global effectiveness of all the mitigation practices, we have been developing a hydrological model spatially distributed using a 1km² grid cell on the whole Region (16 900 km²). The EPICgrid model represents the root zone and the vadose zone. In Wallonia, groundwater tables are more than 30 m deep in 8% of the territory. It is therefore of major importance to fill the gap between the root zone and the groundwater bodies. It allows us to assess the nitrate transfer time and forecast the mitigation measures’ effect in time, space and amplitude. On the ground, runoff and sediment yield are modelled at the small watershed scale. This report presents an complete analysis of the mitigation measures implemented in Wallonia and their effects forecasted until 2015