London sewers unfit to deal with extreme rainfall as toilets blocked up with excrement

The type of heavy rainfall events experienced in London last July are made more common by climate change.

A report from the London Flood Review concluded that the capital’s drainage system is not suited to dealing with extreme weather events, which are only going to become more common with climate change.

More than 1,500 homes were flooded as sewers flooded and toilets backflowed with excrement in July 2021, on two separate days when London experienced above average rainfall.

Sewers can’t cope with extreme rainfall events

The extreme weather event affected 12 boroughs of London on 12 July and 25 of July, with the capital experiencing two months’ worth of rainfall in just a couple of hours.

The London Flood Review report stated: “Such events are likely to occur more frequently in the future, and the various organisations which manage flood risk will need to work collaboratively to ensure that the impacts of flooding are managed appropriately.”

Part of the problem with dealing with such events lies in the fact that different bodies have responsibility for different types of flooding, with the Environment Agency responsible for river flooding, while Thames Water is in charge of sewer floods.

London’s Victorian era sewage system was also seen as being an issue, with the London Flood Review report stating: “the evolution of the cityscape has had an effect on the ability of the sewerage system to cope with the current flows which drain to it, which has resulted in some areas now not being able to cope with a 1-in-5 year event.”

The report recommended setting up a single body to deal with such events, and better data and communication between boroughs whose flood risks may be interlinked. It also suggested green solutions for dealing with high rainfall events, such as “regreening” certain areas, should be explored alongside engineering solutions.

The London Flood Review assessment also highlighted how the same weather event can affect different areas in opposing ways, with sewers overflowing in Kensington and Chelsea because they exceeded capacity; while in Waltham Forest not enough surface water was able to get through the gullies down to the sewers which still had capacity.