Mappings extreme floods with numerical floodplain models (NFM) in France

- Hydrogeomorphological mapping is valid for low energy rivers, such as the Meurthe River.
- Usefulness of the LiDAR for HGM.
- Similarity between a major historical flood and the major bed of the HGM methodology.
- NMF is a representation of a maximum flood surface.
- NMF useful in combination with other flood hazard representation.

For more than 20 years, hydrogeomorphological mapping in France has been considered as an efficient method of flood mapping that contributes to sustainable land development by taking into account occurrences of extreme events. The European Floods Directive (2007/60/CE) requires the production of maps showing water depths during extreme flood events. This article provides an overview of the numerical floodplain models (NFM) methodology, which uses hydrogeomorphological observations and LiDAR DEM data to produce water depth mapping. This article focuses on the NFM realised for the Meurthe River, close to the city of Nancy, France. The NFM methodology initially charts the floodplain from hydrogeomorphological mapping, then uses simple hydraulics for validation, and finally produces water depth maps with GIS processing. The resulting NFM shows good agreement with the historic 1947 flood. This methodology is a simple and complementary solution to hydraulics modelling. It provides a better way to communicate information on the extent extreme floods and shows the importance of hydrogeomorphology in flood hazard study and management.