Limit and prevent floods

Intense rainfall can cause flooding, either by river overflow, groundwater rising to the surface, run-off of large volumes of water and/or mudslides. In coastal areas, there is also the risk of marine submersion during storms or high tides. Floods occur at the catchment area scale, from upstream to downstream and finally to the sea.

In urban areas, heavy rainfall tests drainage and stormwater management systems: stormwater networks, combined sewers, treatment plants, storage and retention basins, or discharges to the natural environment.

Prevention solutions can be costly. That is why we are committed to offering you different solutions and defining with you the optimal action plan.

At the catchment area scale, this may involve:

• Relocating buildings or activities in areas highly exposed to risk
• Developing flood expansion areas upstream of sensitive zones
• Building new structures to protect against floods: dams, dykes, temporary protections and barriers (valves, cofferdams), etc.
• Protecting human activities by preserving ecosystems through differentiated ecological management, land restoration and other nature-based solutions

At the city scale, this may involve:

• Mapping existing structures and networks to improve their efficient management (via a reliable and updated Geographic Information System)
• Analysing the condition and operation of networks, with our proven and effective methodologies (such as our rapid DIAGRAP® diagnosis), with innovative network inspection solutions (such as the family of SewerBall® products) or targeted classic inspections (such as CCTV inspections)
• Maintaining network capacities to avoid overflows with our innovative solutions (such as connected gullies) or optimised maintenance actions (such as cleaning, macro-waste management, etc.)
• Keeping sensitive equipment safe in water treatment plants (identified with our digital twin solutions)

When we are responsible for the stormwater management (like in concessions or O&M contracts), our field teams take emergency measures to:

• Protect human lives (populations and staff)
• Manage the flood in rural areas (thanks to dams, flood expansion areas, etc.) rather than enduring it in urban areas, with a risk of important damages on habitats and high impact on local communities
• Execute crisis management plans as predefined and by mobilising emergency resources as soon as necessary
• Restore critical installations quickly
• Formalise and share feedback from past crises and adjust action plans in a continuous improvement approach, to prevent, limit, or even avoid the next crisis
  

To limit discharges, it is necessary to monitor natural environments at all levels of the catchment area. This involves:

• Restoring aquatic environments: restoring wetlands and watercourses which contribute to slowing the water flows
• Reducing inflows and infiltration in sewage and/or stormwater networks through permanent diagnostics to optimise the volume of water that can be managed by the networks and after, by the wastewater treatment plant
• Better collecting, storing and treating stormwater, through good management of networks, storage assets and treatment plants
• Avoiding discharges thanks to static storage and dynamic network management, with our Aquadvanced Urban Drainage solution, which allows real-time control of sewage networks and forecast modelling to reduce the risk of overflows and spills
  

Saint-Étienne is crossed by many watercourses (streams and rivers). In case of storms, the level of the Furan river can rise by one metre within a few minutes. The city has therefore set up a system to limit pollution discharges and urban flooding in case of heavy rain.

With Aquadvanced Urban Drainage, the management of the urban network has been modernised and digitalised. The system relies on real-time meteorological data coupled with information from sensors installed on the sewage network. It models the impacts of heavy rainfall and allows operating teams to adapt their actions in advance and in real-time.
The performance of the system was demonstrated in June 2015, during a very intense rainfall event: 25 mm of water fell on Saint-Étienne in less than one hour. Thanks to the system, the event was anticipated, the maximum amount of rainwater was sent to the treatment plant to relieve a stormwater collector. A district thus escaped the flooding it usually suffered.