Hydromorphology auditing: a generalized framework at a nation scale to view streams and rivers in their landscape context

International audienceIn Europe, there are less than 10 % of total stream and river length that can be considered as relatively free of human pressures. Historical and contemporary human uses of landscape and watershed has produced situations where several cumulative impacts is very common. In that context, it is essential to analyse properly the risks of hydromorphological impairment and its causes, before defining appropriate restoration measures. We propose a multi-scale hierarchical framework named Syrah for The relational system of water course hydromorphology auditing. It is based on geomorphology functioning principles. This "top down" approach proposed relies on an assessment of large scale "damage risk": damage to processes (flow and sediment transport in particular) and structures (resulting morphology) are at the heart of the assessment. Fourteen types of hydromorphological damage have been identified. These are the most common types and are most likely to be the cause of impact on the ecological state of water courses. To process them, the audit relies on an evaluation of the layers of geographical data, existing databases, and on cross references between this information and the data required for management, programming, decision-making and assessment of restoration actions. "Land Use and Activities" (urbanization, agriculture, transport, energy) and resulting "Artificial Features and Uses", which are identifiable are quantified. Syrah multi-scale approach has been validated on selected regions, representing a diversity of hydromorphological situations and around 10 % of the France territory