Engineering and nature to help fight flooding

Causes and effects of flooding 

Sustained rainfall over long periods, storms, high winds and artificialisation of soil are all causes of flooding, and take different forms depending on whether they occur in rural, semi-urban or urban areas. There are a variety of solutions to manage the risk of flooding of waterways, run-off and breakage of structures. They involve two complementary systems: ecological engineering, which aims to restore the services offered by nature, and containment structures to limit damage.

Ecological engineering: restore nature's intrinsic properties

Wetlands such as ponds and bogs, earth rich in organic forest material and vegetation on the banks of waterways make a positive contribution to water containment and slow down flow, particularly during intense rain events. Maintaining the functions fulfilled by these ecosystems is therefore a lasting solution for fighting water-related climate events. Ecological engineering takes account of the many mechanisms for making improvements able to restore and preserve the functions provided by natural environments.

Slow down artificialisation 

Roads, residences, factories, car parks: in flood-prone areas, built improvements can lead to a worsening of damage caused by floods. In fact the sealing of soil blocks absorption of water, allowing it to flow fast into rivers, which then overflow. Water storage is also reduced by the disappearance of hedges and woodland. To slow down and reverse this phenomenon, certain ecological restoration solutions are effective. They enable living environments to better retain water in the soil and thus balance the hydrological cycle. 

Restore natural river beds

The digging and rectification of river beds, undertaken over the last centuries for the requirements of human activity, reduce the natural flow of water towards phreatic zones, accelerate the pace of its flow and limit its absorption. Hydromorphic restoration initiatives help to restore natural river beds and restore wetlands: oxbow lakes, marshes, non-flooding meadows, etc. Reconnecting them to the river is an effective solution for creating buffer zones in which water is stored during floods.

Improvements and infrastructures 

Containment systems  

Generally built parallel to a waterway or on the coast, these structures are created to prevent water from entering inhabited or sensitive areas, as far as possible. They generally comprise one or more dams, which help block access to docks or banks during a flood. These types of improvements also include road/rail embankments, as well as valve systems and pumping stations.

Hydraulic improvements

These comprise one or more water retention structures, such as flood-retarding dams or flood retention basins. Reservoirs temporarily store excess flows from the rain basin and release them once the flood has subsided. VINCI and its subsidiaries are conducting a number of hydraulic improvement projects: at Saint-Romain-de-Popey in the Rhône, in Seine-et-Marne as part of the Seine Grands Lacs project, but also abroad, on the Hostivar dam upstream of the city of Prague, and in Canada at the foot of the Rocky mountains.