Does the bocage of Brittany (f) mitigate floods ? From scientific controversies to public debate

In a context of sustainable and integrated flood management, it is tempting to favor small actions in the hillslopes and non-structural measures over large hydraulic structures – which may have severe impact on the river ecosystems. However, according to the scientific literature, the effect on flood of actions in the hillslopes (land-use modification, small storage facilities…) is difficult to assess, and their efficiency on flood mitigation varies according to the physical context - which explains contradictory results in different studies. Yet, many authors agree that the mitigation effect dwindles with distance and flood severity. This communication deals with the gap between expectations and scientific results, focusing on the case of bocage, in Brittany, and discusses its causes and the ways to bridge it. Bocage is a landscape where agricultural plots are delineated by hedges. The expected role of hedges on floods is often invoked to protect and promote this threatened traditional landscape, and some people even claim that for flood mitigation hedges are preferable to structures built in rivers . So, the first question addressed here is how to write a synthesis focusing on hedgerows, but also for whom it should be written, and through which medium. But it soon appeared that the main issue is to bridge the persisting gap between scientific and technical professionals on one side, and local inhabitants and associations on the other side.