Does surface runoff mitigation mean flood mitigation? Focus on hedges.

Abstract

In a context of sustainable and integrated development, it would be desirable to limit the use of civil engineering in flood risk management and to favour solutions that are more respectful of ecosystems. However, not all authors agree on the effectiveness of actions in concerning runoff to mitigate floods. In order to apprehend these disagreements, we first present some keys to understanding runoff phenomena, which are more complex to understand and quantify than they seem, especially at the watershed scale that is appropriate for a flood prevention strategy. It appears that actions in watersheds, including planting hedges, reduce runoff to a certain intensity, and that one should be wary of generalizations. It is not a question of dismissing actions in watersheds, but rather of specifying their limits. Finally, the notion of interest or efficiency must be placed in a multi-objective context. The stakeholders have different priorities. It is up to them to define together their multi-criteria analysis methodology, as well as criteria for each of the effects like hydrological (on erosion, local or downstream flooding and water quantity and quality), heritage or environmental.