Combined sewer overflow
Combined sewerage systems are designed to transport a certain amount of rain water as well as normal sewage flows. However, during storms there may be more rainfall than the sewers can handle. Pressure can build up in the sewers which, if not dealt with, would cause manhole covers to lift and sewage to flood roads, gardens and even homes.
To prevent this, combined sewers have emergency overflows that allow excess water to be discharged into a nearby watercourse and reduce the pressure in the sewers.
We have hundreds of combined sewer overflows around the region. Modern ones work in such a way that only liquid is discharged and the sewage's solid content is kept within the sewer. We have a number of older overflows and these are being replaced with modern ones in the next few years as part of our investment in environmental improvements.