Flood mitigation designs with respect to river ecosystem functions—A problem oriented conceptual approach

We formulated five proposals to improve specifications of flood hazard reduction projects and five proposals to preserve the river ecosystem functions, based on literature and authors’ experience. Starting from these, we established a conceptual approach using the notion of riverscape, with related function richness and bioassessment tools. We defined four riverscape types based on the gradient of artificialness, from type I (impervious bed) to type IV (less than 30% or no artificial bed). To apply our approach to dry dam designs, we individualized different parts of dry dams and characterized them by an ideal riverscape type, according to the hydraulic constraints of each part. Type I is unavoidable in the bottom outlet, and types I or II at the foot of the dam. Types III (30–50% of artificial bed) and IV were recommended at upper and lower parts of the dam, according to the risk of bank erosion and need for bank reinforcements. The approach appeared efficient to help biologists and hydraulic practitioners work together, and find technical solutions complying with both flood protection and biodiversity preservation requirement.