Managing rainwater is essential in a collective water and sewerage network, particularly in urban areas.
The ground is impermeable and heavy rain can cause flooding. The first rain to fall becomes polluted when it comes into contact with the ground or buildings. It can also saturate existing infrastructure, in which case it overflows into watercourses and causes pollution. Local authorities build storm basins to address these environmental problems.
The original 50-year-old system of tunnels was designed to drain rainwater from the highway and surrounding districts. A series of urban development projects in this 12.5 square kilometre drainage area then increased the volume of water that needed to be handled by the storage tunnels.
A rainwater storage basin project was therefore developed to avoid the risk of flooding, its main objective being the construction of a basin that could contain flooding in the event of a 24-hour rain event with a 10-year recurrence interval!
To achieve this, six inter-connected diaphragm wall wells (14m in diameter and 34.5m deep with a 1.2m-thick wall) will eventually be built by Nicholson Construction, a Soletanche Bachy subsidiary in the USA, along with a pumping station to evacuate water and control the risk of flooding along I35W.