Heavy rainfall in the city of London can cause many problems for the decades old sewer system. When rainfall levels are higher than normal the Victorian sewer system cannot cope with the amount of waste water that needs to be sent to the local treatment works, so instead it flows though emergency overflows into the River Thames.
To improve the water quality in the river and to bring the city in line with current environmental thinking, a super sewer has been proposed underneath the city, roughly following the current line of the river. Built at a depth of 75 metres this super sewer will be able to collect and transfer the excess rainfall from the Victorian system to improved treatment works on the outskirts of the city.
It is hoped that when the super sewer is complete that the 34 most polluting discharge points along the river will instead have their discharges sent to the Becton Sewage works in the east of the city. The cost for the completion of the work has been estimated at £4.1bn and construction has been provisionally scheduled for 2016.