Preventing sewer flooding
The damage caused by sewer flooding can be devastating. We're doing everything we can to prevent it happening now and working on a long-term solution too.
There are also some easy things you can do to prevent sewer flooding at home.
Our investment in sewer flooding prevention
We're constantly improving and developing our sewer system. Our investments include:
We're using CCTV surveys to identify structural defects in the assets such as cracks, fractures, holes and collapses. This allows us to find issues before they cause sewer flooding.
We review the CCTV survey data to determine the relevant type of work needed to fix the pipe. This information feeds into our sewer rehabilitation programme.
Sewer rehabilitation programme
The sewer rehabilitation programme aims to restore damaged sewers to a good structural condition. We use different rehabilitation techniques depending on the type of damage. This includes:
- Relining the whole length of a sewer between two manholes with an epoxy resin liner
- Covering a small section of damaged pipe with patch repairs
- Excavating and replacing the old pipe with a new section
We have a maintenance programme for regular sewer cleaning and inspections. We carry out acoustic surveys to check if the sewer needs cleaning. Then we use sewer jetting equipment to remove material from the sewers. This reduces blockages which can cause sewer flooding.
Over 80% of sewer blockages are caused by fat, oil and grease or paper and rag (including wet wipes). Most of the planned cleaning is to remove this type of material.
We also carry out specialised work, including:
- cutting roots from trees and vegetation
- descaling sewers
- removing silt and other material that may have washed off the roads
Interceptor trap removal
Interceptor traps are U-bends on the outgoing pipe of some manholes. They're usually found on the manholes in front of older properties. If they get blocked, they can cause sewer flooding to homes and gardens.
Over 20% of the blockages that we clear are at interceptor traps. The interceptor removal programme targets locations with repeat blockages and sewer flooding risk. We're replacing the U-bends with straight pipes, so sewage can flow more easily through the network.
The aim of the customer education programme is to reduce sewer misuse in the waste network. Over 80% of sewer blockages are caused by fat, oil and grease or paper and rag. This is mostly due to misinformation, lack of alternatives and habit.
We want to raise awareness and make it easy for customers to access advice and information. We now contact all residential properties within 30 metres of a sewer misuse related blockage. First by postcard and letter, then escalating to face-to-face visits if the issue doesn’t get resolved over a few months.
Sewer depth monitors
Sewer depth monitors (SDM) are installed inside a manhole chamber to track the depth of sewage flow. We use their data to remotely monitor the performance of the network.
Each SDM has an alarm level set. If the sewage in the manhole chamber rises above this threshold, then the alarm triggers. We can then arrange to visit the site and investigate the issue.
We have over 12,000 SDM across the waste network, with an ongoing installation programme. We prioritise repeat blockage locations. This is to reduce the risk of property sewer flooding or pollution to watercourse.
Rising main rehabilitation
Our burst main rehabilitation programme reduces the risk of sewer flooding from burst rising mains.
A rising main is a wastewater pipe that pumps sewage uphill. This means the pipe is always under pressure. When a rising main fails, it's usually in the form of a burst. This causes an escape of sewage that can lead to pollution incidents and property flooding.
Our rehabilitation program aims to improve the condition of a rising mains and prevent future incidents.
Tackling surface water is key to preventing our sewage system from getting overwhelmed during periods of heavy or prolonged rainfall. This is becoming a bigger issue with climate change creating more intense storms, and development meaning the loss of green spaces.
Our focus on surface water management includes:
Correcting misconnections of surface water to a foul sewer
When we find a misconnection, we divert surface water to an appropriate system. This could be a surface-water sewer, watercourse, land ditch or even a soakaway unconnected to the foul sewer.
Working with other surface-water risk management authorities
We're working with third parties to see how we can replicate natural run-off processes. This would mean our surface water systems are less likely to be overwhelmed by rainfall. This is a problem that will only become more challenging with climate change.
It's important that restaurants manage grease and food waste responsibly, to avoid blockages that can cause flooding. Our network protection team visits food service establishments (FSE) to advise and educate. We check compliance, then work with them to improve processes. This could be, for example, by installing a grease trap.
There is a staged escalation process. If an FSE is persistently misusing the sewer, our team can prosecute. We'll recover costs for damage to the network and associated maintenance work.