Types of storm overflow
The annual return gives each outlet an asset type. The type tells you where in the sewer system the overflow sits.
What to do
Read the outlet type on the outlet page to see whether the overflow is on the sewer network, at a pumping station or at a treatment works. The type does not tell you how much it discharges.
Overflows on the sewer network
More than half the outlets in the return sit on the sewer pipes, away from a treatment works. Many sewers carry rainwater as well as sewage. In heavy rain the overflow lets excess flow out so that the system does not back up into homes and streets.
Pumping stations
Pumping stations move sewage along the network. A storm discharge at a pumping station releases flow when more arrives than the station can pass on.
Treatment works
An inlet overflow releases flow before it enters a treatment works. A storm tank holds excess flow during rain, which can go back for treatment afterwards. When the tank is full, it can discharge. The return marks some assets “with treatment” when it records treatment before discharge.
Names and codes
Outlet names come from the company and often include codes such as CSO (combined sewer overflow) or STW (sewage treatment works). The name and the asset type are separate fields, so check the type on the page.