Finding its natural bed: a natural thing for the Yvette

The Yvette is a river known to be capricious, especially when it has decided to leave its bed. A character with which BG must cooperate, as it was assigned by the Intercommunal Syndicate for the Hydraulic Development of the Yvette Valley (SIAHVY) to ensure the restoration of the ecological continuity of this almost 40 km long watercourse and improve flood protection for inhabited areas.

The 2016 Yvette flood is etched in the memory of residents. No wonder, since the flooding had been of an unprecedented scale and the damage described as exceptional. Mandated by the Intercommunal Syndicate for the Hydraulic Development of the Yvette Valley (SIAHV Y), BG is doing everything possible to prevent such situations from happening again. The Group is not only carrying out studies and project management to improve flood protection for inhabited areas, but is also working on restoring the ecological continuity of the Yvette.

One of the main interventions by BG will consist in the renaturation of the banks, that is to say a return to “natural”. “During the last century, civil engineering techniques, such as the use of concrete, sheet piles or contiguous pile walls, have been favoured to stabilize the banks of rivers and rectify their paths. The problem with this type of development, called anthropogenic, is the obtaining of recalibrated and strongly channelled rivers, as well as an impoverishment of the environments and habitats necessary for good biological quality. In addition, this results in an increase in flow velocities, which accentuates erosion phenomena,” explains Fabrice Dupont, head of the River hydraulics group.

To restore mobility to the rivers and improve their hydraulic operation, Fabrice Dupont and his team will remove a number of structures, such as dams and dikes. The slopes of the banks will also be softened. These measures will make it possible to restore an aquatic life cycle, in order to recreate an adapted and diversified physical environment for fauna and flora, and will boost the development of natural environments.

Regarding flood protection measures, it is notably planned to restore the flood expansion field in a wooded area south of a college. “The idea is to create a space in an uninhabited area where flooding can be encouraged during floods,” explains Fabrice Dupont. The project led by BG also includes a cycle path along the river. “In agreement with the SIAHVY, it is a rich and enjoyable living environment that we are helping to develop for residents,” he adds.

BG who started its studies in 2019, still has significant work to do. “We signed a four-year project management agreement with SIAHVY. It is therefore an enormous amount of work that is also extremely interesting,” says Fabrice Dupont.

(Article taken from BG Magazine 2021, updated version on the site)