London flooding response
In July 2021, London was hit twice by extreme rainfall, which led to widespread flooding. At its heaviest, a month’s rain fell on some parts of the capital in just one hour.
This tested our sewers and local authorities' drains and gullies. The speed, severity, and scale of the rainfall was beyond the limits they were designed to cope with. This led to the flooding of more than 2,000 properties.
Forecasts suggest severe rainfall will become more common due to climate change. So, we've taken the following actions to reduce the impact of such storms.
1. Thames Water review
We know the service we provided our customers with following the storms was not good enough. Many people were unable to contact us and our teams were slow to get to some of the worst hit areas.
So, we carried out an internal review to examine the actions we took before, during and after the storms. This helped us to identify what we could have done better so we can develop these actions for next time.
2. Sewer network review
We wanted to find out if our sewer network may have worsened the impact of the extreme weather. This would help us to understand why the flooding in July 2021 was so severe.
For a transparent and impartial process, we commissioned an independent assessment. This was carried out by a group of experts and chaired by Mike Woolgar.
The independent report had four core objectives:
- Research, understand and report on the “what, when, why and how” of the two July storms
- Examine the flooding mechanisms. Consider the performance of drainage systems against design standards. Focus on Counters Creek and Maida Vale Flood Alleviation Schemes
- Consider changes to existing and planned drainage system works, operations or policies. Determine if they could've alleviated flooding and make London resilient to future storms
- Be as evidence-based as possible
The review is now complete and will help us put a plan in place for future incidents.
3. Sewer flooding surveys
To support our customers, we offered sewer flooding surveys for affected properties. We contacted over 3,000 customers who may have been impacted by the July 2021 storms. We promoted the offer through local events, social media and community groups. We also collected responses from affected customers through an online questionnaire. In total, we surveyed almost 1,000 properties in the affected area.
Sewer flooding resilience devices
For high-risk properties identified as suitable for individual mitigation, we installed tailored devices. The devices used included:
Forge non-return valve
These are one-way valves used for properties that can’t be connected to a large trunk sewer. They’re often put in the lightwell of a property or outside the boundaries in the road.
WaStop non-return valve
These are one-way valves used when properties are connected to a large trunk sewer. The sewer must be safe to access and wide enough for an engineer to go into and install one.
Flooding local improvement process (FLIP)
These are one-way valves with added pumps. They push flows from the property into a full sewer, when the valve is closed. We may install a FLIP if there's a risk to life or higher risk of flooding.
Counters Creek performance commitment report
Ofwat asked us to report on performance within the Counters Creek catchment. This includes the risk of flooding and level of resilience.
Read the full Ofwat requirements for this report. The requirements can be found in section 1.2.37 (pg 153) of the Ofwat PC commitments.