The Serein River: a lovely leaky catchment

The Serein River (the adjective "serein" means serene, calm) is a tributary of the Yonne River which then feeds the Seine River. The Yonne River is known as the "unruly child" of the Seine basin, as it is one of the tributaries with the flashiest response. In spite of its limited size (10,887 km²) in comparison with the Seine basin in Paris (43,800 km²), the Yonne River generates important amounts of water. Its flood waves are fast and reach Paris in 3 or 4 days. This may cause significant problems in terms of operational forecasts for the flood forecasting service (based at the Regional Direction for Environment DIREN) in charge of flood forecasting in the Paris area. The Serein River which contributes to this specific behaviour shows complex generation mechanisms and propagation of floods. However this complexity does not seem to originate from the spatial distribution of rainfall. Usual simulation and forecasting models do not simulate this complex hydraulic behaviour with a good enough accuracy. Therefore the DIREN decided to carry out a study to better understand the hydrological and hydraulic behaviour of the catchment and to improve modelling tools. To overcome modelling difficulties, a simulation scheme that couples a rainfall-runoff and a full hydraulic model was developed. The coupled model is evaluated on past observed events. This scheme should provide more accurate flood simulations to let forecasters issue forecasts more serenely on the Serein River.