Development of an innovative water hazard and risk management strategy based on a pilot integrated modeling tool on the sensitive Thau Lagoon in France

The lagoon of Thau, located in the South of France, is a famous area, particularly attractive thanks to its geographical and economical context that is based on fishing and marine cultures, balneology and seaside tourism. The development process of the 14 municipalities that are located on its watershed is then completely bounded to the lagoon pollution control.

The lagoon was downgraded couple of years ago for not having reached the required quality conditions. Because of its environmental and economical pressure, the SMBT has been created in order to improve the situation through an efficient and adapted water hazard and risk management on the watershed. The office decided to develop and implement an innovative approach based on an integrated modeling of the entire water system.

An integrated superficial flow model was developed on the whole watershed and combined with the lagoon model. This pilot superficial flow model includes the sewer systems as well as the watersheds and rivers on the same interface. The water quantity and quality, including Nitrogen, Phosphorus and Ecoli, can be simulated in any part of the territory through a 1D or 2D approach. The dynamics of the flow as well as the pollutant behaviors can be estimated anywhere, including in the lagoon. The model was successfully calibrated on various continuous and storm events for both quantity and quality aspects. This unique model is used by the SMBT for 2 main objectives: (i) the water risk forecasting for both the quantity and quality aspects and (ii) the hydraulic development planning on the territory.

For the forecasting part, a library of many scenarios was created by the model based on various hydro-meteorological conditions. All the potential risks were considered in order to be able to manage in real time the flood, the bathing, the conchylicole activity, and the sewer network. Again, both the quantity and quality aspects were considered. Then based on the sensors measurements collected in real time on the territory as well as the hydro-meteorological forecasts, a platform is automatically selects and gives the predicted risk to expect on the area. The actors (municipalities, state, professional workers, partners…) can then decide which actions to take in order to avoid damages and loss.

For the hydraulic development part, the most sensitive areas of the territory can be identified with the model results in terms of both quantity and quality aspects. The SMBT can then organize its actions planning depending on the priority level.

The model is also regularly and successfully used as a powerful communication tool. Thanks to its user-friendly interface, the hydraulics works can be clearly presented and explained in a very didactic and open way, which facilitates the understanding for non hydraulics expert people. This aspect should not be neglected since the development acceptance by everybody is a guarantee for a harmonized and attractive context.