Wednesday 22 December 2021

Independent London Flood Review announced into flooding events of July 2021

The London Flood Review has been set up to examine the flash flooding that affected many parts of the capital in July 2021.  The review seeks to better understand the extent and causes of these floods, to assess how the drainage systems performed, and to recommend how the increasing risks of future flooding events can be managed.

The review, which has been commissioned by Thames Water, will play an integral part in ensuring the company future proofs its infrastructure to protect its customers, their communities and the environment as such severe weather events look set to become the norm across the UK.

The review will also play an important role in improving collaborative working between all parties responsible for managing future flooding risks. As part of its focus, the review will provide insights on London’s wider drainage infrastructure and broader recommendations that could be adopted by all organisations with surface water management responsibilities.



Terms of Reference

1. Why has Thames Water commissioned an independent review?


On 12 and 25 of July 2021, London experienced extreme rainfall events that led to extensive flooding, with more than a thousand homes and businesses flooded, and health, social and transport infrastructure also affected. Given the scale of the impact on its customers and local businesses, Thames Water has taken the unusual step of commissioning an independent review into the flooding as the organisation believes it is important to understand the root cause of the flooding, how its assets performed and to learn lessons so the company and other parties may better prepare for future risks, in an open and transparent way.

This review will also assist with Thames Water’s role (as a Risk Management Authority) in supporting Local Authorities in undertaking their flooding investigations as required by Section 19 of the Flood and Water Management Act (2010). Thames Water’s ambition is that the review should take no more than 6 months, with interim reports published as it progresses. This timeframe is planned so that the review concludes within a period where the findings are relevant to the key stakeholders and also are able to inform Thames Water’s draft PR24 business plan. As such, the review must balance the desire for comprehensive scope, level of detail and stakeholder engagement, with the need to complete within this timeframe.

This will mean that the review will primarily focus on the performance of Thames Water’s assets, within the context of other Risk Management Authorities’ assets, and be developed using existing Thames Water models.

A Brent Council spokesperson said: 

Brent Council welcomes the Independent Review into the flooding events of last summer that has been commissioned by Thames Water . We look forward to working with the review body to inform it's evidence base and to assist the review to meet its objectives.

2. What is the aim of the independent review?

The review has four core objectives. To:

1) Research, understand and report on the ‘what, when, why and how’ of the two July storms


Key to the investigation is capturing as accurately as possible what occurred, where and how customers were affected, i.e. the number and type of properties impacted, the type of flooding (internal/external, surface/sewer) they experienced etc. This needs to be undertaken in the context of understanding the storms that occurred i.e., characteristics of rainfall and also where it occurred because the impact will not be the same across the different affected areas. This will also identify whether there were other factors (such as high tide, time of day etc) that potentially contributed to the flooding and what impact
they might have had.

2) Examine the flooding mechanisms and to consider the performance of drainage systems against design standards.


This will determine how well Thames Water’s assets performed on 12 and 25 July in accordance with the duty set out in Section 94 of the Water Industry Act.


 The assessment should be of Thames Water’s drainage and sewerage assets in general in the affected boroughs, with a specific focus on recent flood alleviation schemes, including Maida Vale, Counters Creek and Westbourne Grove and their performance against their project objectives (this will include where Thames Water has installed FLIPs and other local flood risk management measures).

3) Consider how changes to existing and planned drainage system works, operations and/or policies might have alleviated the flooding and make London more resilient to future storms.  


Whilst the focus of the recommendations will be on the public sewerage system, these must be made within the context of the interaction between the Thames Water operated and maintained public sewerage system and third-party drainage and flood risk management systems. The review should highlight wider points on the future of the London’s sewerage and drainage system and identify key opportunities that should be considered in Thames Water’s DWMP and PR24 Business Plan, and other stakeholders’ plans and programmes.

4) Be as evidence based as possible.

Further lines of inquiry may be included as raised by the participants of the review, but as noted previously, these should not detract from the aim of achieving the core objectives within the stated timeframe.

3. How will the independent review be run and managed?

In order to be properly independent, the review cannot be led by Thames Water, but neither can it be entirely independent of Thames Water, as Thames Water is the major provider of information and resources for the review and will be a key recipient of its recommendations.

The structure of the Independent review is as follows:

1. An Independent Expert Group (‘IEG’) that will lead the review. The IEG’s role is to:
a. Agree the terms of reference and scope for the review, including the brief for thecontractors, in consultation with the Strategic Stakeholder Panel
b. Work with Thames Water to appoint the contractors to support the IEG
c. Work with the contractors to produce the interim and final reports in consultation with the Strategic Stakeholder Panel
d. Be responsible for the successful outcome of the review
e. Stand behind the findings of the review
f. Promote the review and the dissemination of its findings, including attending any potential scrutiny/inquiry meetings.

The IEG will consist of three experts with industry-leading knowledge and experience in sewerage and drainage modelling, legislation and regulation, and flood risk management. The experts will be appointed by and paid by Thames Water, but be otherwise independent.

A key early stage to the review will be an assessment by the IEG of available data/models in order to agree what gaps may exist and how best to resolve these gaps within the time available.

2. A Strategic Stakeholder Panel (‘SSP’) comprising representatives from the key strategic organisations in London with a responsibility for and interest in surface water and sewer flood risk management. The SSP will be consulted on the scope and objectives of the review, inputting into its course, receiving, and (where appropriate) endorsing, promoting, and
enacting its findings. The SSP will include senior representatives from:

a. Greater London Authority
b. Transport for London
c. London Councils

d. London Drainage Engineers’ Group
e. Environment Agency
f. Consumer Council for Water
g. Ofwat (as an observer)
h. Thames Regional Flood & Coastal Committee
i. Thames Water

The IEG will, as a minimum, meet with the SSP at each key stage (see ‘Key Deliverables’ below):
• Inception meeting to discuss and agree the Terms of Reference
• Meeting to review the work programme and agree data requirements from the SSP and other parties
• Review the findings of each stage of the review ahead of publication of the interim reports
• Review the findings of the final report and development of a non-technical summary

3. A contractor (Mott McDonalds) to provide the technical capability and resources to undertake the work detailed in a brief approved by the IEG. The contractors will be procured and funded by Thames Water, but report to and be managed by the IEG.


4. Key Deliverables

The following key deliverables are included to provided structure and clarity around what outputs are required. It is intended that each stage will build on the prior one:
• Stage 1: Full assessment of impact of the storms, detailing the nature of the storms that occurred and the impact (extent) of the flooding (who and what was flooded).
• Stage 2: Assessment of the flooding mechanisms and a technical view of where and how  flooding occurred.
Stages 1 and 2 together will form the ‘baseline statement’ for the review:
• Stage 3: Explanation of the performance of the sewerage system, including stating whether the sewerage system and key flood alleviation schemes performed to the intended levels of service.
• Stage 4: Lessons learnt - details of where improvements to the sewerage system and potentially third-party assets and policies may be appropriate. To be completed by end of April 2022.

A report will be published for each of the stages.


1 comment:

David Walton said...

This invetigations terms of reference will be pivotal. For example, the River Westbourne which historically floods and floods repeatedly, is for all reponsible agencies in consensus (including all local politicians) categorised as being simply a sewer!

Until this entrenched lack of environmental expert attention changes the situation regarding remediation, attenution, even not tall building next to this river (as if it is lowest level flood risk) remains a colonial development fix which local people must "learn to live with" and learn to pay for.

South Kilburn is urban project zone "the worse the better," but can South Kilburn sewage flooding of the Maida Vale Conservation Area sustain these roaring 2020's?