Vendredi 4 janvier 2013

Proposition de méthode agro-environnementale pour la gestion des crues.

Martine LEJEUNE (RIOU) | WP2 - Rétention naturelle de l'eau

Floods are common in Belgium, and specially in one of its larger basins, the Meuse River. Heavy rainfall on the Ardennes mountains causes the few rapid flowing rivers draining this high plateau to inundate in a delay as short as a couple of hours the Meuse Valley in Belgium, and thereafter the lowlands in the Netherlands. Protecting these highly populated and industrial areas is a major issue. But dams and dikes will not do the job alone.

Experts say flood management is greatly supported by water retention in the upper part of watersheds. The idea of using agricultural land – and more specifically grassland – as retention zones has been developed by many regions in Europe. Though Wallonia do not have yet a specific measure dedicated to water retention in agriculture. Therefore this report presents the specifications for an agri-environment measure « Grassland flooding » which should be implemented in the future propositions for the Walloon Program for Rural Development 2014-2020.

The measure itself consists in flooding permanent grassland plots thanks to a propitious natural land shape, or with the help of small earth dams. Inundation comes either from surface runoff  (for plots on plateaus and slopes) either from rivers overflow, and it must be temporary. The plot must still be adequate for grazing and mowing. The specifications include 1) no drain and no maintenance of actual drainage systems, 2) local flow retention eventually with small dams, 3) free meandering, 4) no fertilizers nor pesticides on the potentially flooded part of the plot (plus a buffer zone), and 5) planning of grazing and mowing.

The specs and the farming practices should ensure the relevance of the measure in flood control, but also in wet grasslands or riparian land restoration expecting a positive impact on biodiversity as well as on surface water quality.