Assessing the effect of a catchment-scale restoration project in Wallonia (Belgium)

In the context of fulfilling the Water Framework Directive requirements, the LIFE+ project Walphy allowed experimental restoration projects to be undertaken on two medium-size catchments of the Meuse basin in Wallonia (Belgium) between 2009 and 2014.
Before undertaking sustainable rehabilitation measures, a multi-scale assessment of hydromorphological conditions (catchment, stream and site) was conducted. It was based on a variety of variables characterizing the river system and its geomorphic processes (e.g. sediment transport), along with human-induced disturbances (e.g. barriers to river continuity).
The Bocq catchment has been subject to a large-scale restoration project through the removal or modification of 20 barriers (mainly old weirs), reconnecting the Bocq with the Meuse. In addition, 2.6 km of straightened courses were improved by restoring meanders or diversifying habitats through a wide range of rehabilitation techniques.
The success of the restoration projects was evaluated on the basis of a multi-disciplinary monitoring. We compared hydromorphological parameters and biological diversity of benthic invertebrates, fish and macrophytes. 2-3 years post-rehabilitation, hydromorphology was significantly improved. Depending on the rehabilitation measures, the restoration effects observed for invertebrates and fish differ. Weir removal and restored meanders have resulted in the most positive effects, while habitat diversification has led to more contrasted results, depending on the level of ambition. The geomorphological monitoring has focused on the effectiveness of spawning gravel rehabilitation and the effect of barriers on sediment transport. Topographic surveys and the use of pebble tracers have highlighted a natural bedload transport following a weir removal.