Hydrological modelling of the EU Nitrates Directive Actions Programme: new developments in the Walloon Region (Belgium)

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. At the same time, the government decided to fund non mandatory practices focused on agro-environment. Some of these (like buffer strips) should also be useful in nutrient mitigation.

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 in order to assess buffer strips’ effect on sediment deposition and its consequences on N and P mitigation.

The poster will explain the more recent results that consist in forecasting action plans’ effect until 2015 (on both surface water bodies and groundwater bodies) and modelling of the current buffer strips’ effect.