How can modelling assist decision-making in flood management and the implementation of prevention measures? The case study of Hauts-de-France.

Faced with increasingly severe climate change, some areas are having to cope with more extreme natural events. This was particularly true of the floods that hit the Hauts-de-France region (France), and more specifically the Pas-de-Calais department, in 2023.

Our study is part of an approach to prevent erosion and flooding in this region, with the aim of assessing the impact of sedimentation on bank erosion, but also to see how the implementation of new developments such as controlled flood zones could limit water stagnation. After analysing the characteristics of the areas concerned, peak flood flows for return periods of 10, 20, 50 and 100 years were estimated using hydrological and hydraulic modelling tools. Thanks to these simulations, we can identify areas prone to flooding on several sections of each catchment area.

The methodological approach includes statistical analysis of rainfall data using Hyfran-Plus software, extraction of geometric data from the hydrological network via ArcGIS, hydrological modelling to simulate rainfall-runoff transformation using HEC-HMS, and hydraulic studies to delineate and map eroded areas using 2D modelling with HEC-RAS, integrating the geometric and hydraulic data needed to simulate current conditions in the event of flooding.

The results of this hydrological modelling made it possible to estimate the peak flows specific to each area studied, providing key information for the design of structures to protect against natural hazards. The hydraulic modelling highlights several sensitive areas along watercourses with a high risk of overflow and erosion.

These results not only identify areas at risk, but also guide preventive measures, such as reinforcing riverbanks, installing retention basins and updating hazard maps for local authorities.