Different methods are used in hydrological and hydraulic modelling in a catchment. Deterministic modelling can be used to produce detailed information and optimize the organization of massive data collection. In the catchment of Paillons, there is a need to improve knowledge of hydrological processes through deterministic modelling. In fact, Nice Côte d’Azur metropolis faces numerous challenges in the Paillons catchment. The area provides water resources for large communities. However, it is exposed to flooding and droughts. Complex hydrological processes generate runoff over the 246 km2 watershed. Few existing monitoring stations provide runoff data. In addition, there are limitations in the understanding of surface hydraulics. Thus, this study uses DHI Mike21FM for surface hydraulics with 5 m grid size for riverbed and 2 m for tunnels. The study area is limited to the lower Paillons River. Observed and modelled water depths vary between 0.1 and 0.5 m for a maximum discharge of 38 m3/s in the tunnels. Flood maps created with a discharge of 1000 m3/s, show clearly high flood risk zones and flow directions. The selected CFL condition under 0.8 is respected. The tool is suitable for modeling flooding in areas of interest within the catchment of study. The results obtained are satisfactory and demonstrate that the constructed tool makes it possible to reproduce the overall behavior of surface hydraulics.
Nice Metropolis in Alpes Maritimes, France is prone to flood. The city is crossed by the Lower Paillons River (LPR). Its discharge for a return period of 100 years is estimated at 794 m3/s. Part of the river is covered by 2 km. In addition, there are two retention storages in the river bed and a floodable road tunnel on the left bank. Due to the increase in urban development, flood management is challenging. An existing decision support system (DSS), Aquavar, uses DHI Mike tools to reproduce runoff for the Lower Var River in the same region. To extend this system to the LPR and reinforce flood management, a new modelling tool adapted to the characteristics of the LPR is needed. Consequently, this research utilizes the DHI MIKEPLUS tool to develop a 1D–2D coupled model for real-time flood management. The results demonstrate that flood events like those in 2017 and 2019 were correctly reproduced. The linear regression R2 is above 0.8 for all stations. It was also estimated that the covered river (CR) should stay clean to avoid widespread flooding in the urban area. Overall, the model is useful for simulating flow in real time and can help sustain urban development.
The French Mediterranean region is vulnerable to flooding caused by extreme rainstorm events. To better predict floods and anticipate consequences, the technical managing services operating on the field need to analyze the hydrological situation, receive accurate forecasts and issue alerts to the exposed population. Within this context, the various needed modelling tools are integrated within a common framework of a Decision Support System (DSS). This approach has been developed and implemented in the Cagne catchment located in the French Riviera. The Cagne catchment covers 96 km2 area and it is densely urbanized with high risks of inundation in the downstream area. The hydrological model MIKE SHE covers 96 km2 with a 20 m resolution. The river network is represented in a 1D MIKE 11 model by 18 branches and 1899 cross sections. The downstream area is covered with a high-resolution hydraulic model built with MIKE 21 FM. The model receives inputs from the hydrological model and can produce detailed inundation maps and forecasts. A major rainfall event observed from October to December 2020 is currently used as validation situation and the built modelling system has demonstrated its efficiency to reproduce the observed processes and to deliver the forecasts on due time.
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