Deep storage tunnels

Cities with old combined sewer systems overflow raw sewage into rivers during heavy rain. This pollutes waterways and harms public health.

Large underground tunnels capture overflow during storms and hold it until treatment plants have capacity. The stored water is then pumped out and treated normally.

Deep bored tunnels, connection shafts to existing sewers, pumping stations, treatment works

Flow sensors in sewers and tunnels, rainfall gauges, SCADA control systems

Captures the vast majority of overflows; long design life (100+ years); works with existing sewer network

Very expensive (billions); takes years to build; does not reduce the volume of stormwater entering the system

Operational scenarios where this pattern is applied:

• Detect and report sewage overflows —

Real-world examples of this pattern in action: