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Independent Reservoirs

Volume 673: debated on Monday 16 March 2020

On 3 September 2019 the then Secretary of State, my right hon. Friend the Member for Chipping Barnet (Teresa Villiers), commissioned an independent review following the Toddbrook reservoir incident (31 July-1 August 2019) where part of the spillway collapsed following significant heavy rainfall. The damage did not breach the reservoir dam itself, but as a precaution, some 1,500 people in Whaley Bridge were temporarily evacuated while the dam was made safe. The review has been led by Professor David Balmforth, supported with technical expertise from Dr Peter Mason and Dr Paul Tedd. The review panel has provided me with a comprehensive report. This sets out their findings into what might have led to the damage and whether there was anything that could have prevented or predicted it, and identifies lessons for wider reservoir safety. (Full terms of reference for the review are on

I would like to thank the review panel for their detailed investigation of what led to this incident.

Report findings

This report explores the causes of the spillway failure at Toddbrook and concludes that a combination of factors led to the partial collapse last August. It has identified that the original design of the auxiliary spillway was

“inadequate and not fit for purpose” and that this was “exacerbated by intermittent maintenance over the years”

which when combined with the level and force of flow over the spillway at the end of July ultimately led to the partial collapse on 1 August. It has not been possible to determine which factor was the primary cause of failure on the day, and the report finds that:

“ With consistent good quality maintenance over the years leading up to the event, the spillway might not have failed during this event. However, it would have been unlikely to survive the probable maximum flood which is many times greater than the flood in which it failed”.

The report identifies that there may be a lack of understanding of the risks to spillways within the reservoir community, and has made recommendations to address these. For example, the design concerns had not been identified previously, including at inspections prior to 2018, and the report notes that

“had the drawings been reviewed at the time of the 2010 inspection, the deficiencies in the spillway design might have been identified then and remedial action taken”.

Good practice examples have been highlighted, and used to inform recommendations for the whole reservoir community—this includes the provision of a package of historical information to inspectors, such as the original design drawings that were provided by the Canal and River Trust’s (CRT) supervising engineer for the 2018 inspection. These were used by the inspector to identify potential concerns relating to the spillways longer term viability leading to a requirement under a measure in the interests of safety (MIOS)1 for CRT to investigate further.

The review also found that communication between those involved could be improved and strengthened for the avoidance of doubt in the future. The inspection report

“was written in a style often found in inspection reports”,

but this

“did not convey any sense of urgency or require any precautionary measures”

which the CRT then relied on to determine their work programme. It further identified that although the inspector provided initial feedback on the need for a robust maintenance programme to CRT engineers at the time of the inspection, “it would appear that this had not been completed some eight months later when the incident occurred”. It was not until the CRT received the final inspection report in April 2019, combined with internal arrangements to communicate earlier, that full consideration was given to any of the required actions. The review panel find that

“Given the significance and credibility of risks to the reservoir, our view is that more could have been done to communicate the urgency of the MIOS and statutory maintenance to the owner at an earlier stage”.

As a result of his review, Professor Balmforth reports that compliance with the current legislation is good:

“Overall there is 97% compliance, so reservoirs are believed to be safe”, but have concluded “... as the incident at Toddbrook so aptly demonstrates, a compliant reservoir might not necessarily be safe”


“There is clearly a need to close the gap between compliance and safety”.

Report recommendations

Professor Balmforth has made 22 recommendations in his report for application across the reservoir network and community. These include:

Eight recommendations covering the inspection of reservoirs covering improved guidance, detailed inspections of spillways and the wording and timing of reporting to owners.

Two recommendations on the supervision of reservoirs covering the reporting of condition by supervising engineers and the actions needed by the responsible person(s) for safety within the owning organisations.

Four recommendations proposing further work is done to consider the implementation of or changes to the current legislative framework.

Five recommendations for improved operations and maintenance, including the responsibilities of the owners and greater powers for the regulator to enforce statutory maintenance requirements.

Three immediate actions to be taken as a result of the spillway design concerns identified at Toddbrook, which are already in hand.

The Government have accepted all the recommendations.

A full list of the recommendations and the Government response to each one is in table 1 in the attachment. The report will be published today on uk/government/publications/toddbrook-reservoir-incident-2019-independent-review.

Incidents such as that at Toddbrook are very rare and this report confirms that we have a strong record of reservoir safety and that compliance, including by the Canal and River Trust, with our safety regulations is good. We should not, however, be complacent and need to ensure our approach continues to be fit for purpose, so I will be asking Professor Balmforth to lead a second stage review, which will undertake a wider assessment of reservoir safety legislation and its implementation.

Reservoir safety work already underway

DEFRA and the Environment Agency have contacted all large raised reservoir undertakers to identify any which may have similar design concerns to those found at Toddbrook. Any identified will be expected to have an urgent inspection/investigation to ascertain what remedial work may be needed. The Government will also consult on making a requirement for all large raised reservoirs to have an emergency contingency plan in place.

DEFRA commissioned a research study into small raised reservoirs in 2017, which has recently been completed. The report will be published shortly and includes evidence about the number of small raised reservoirs and the risks they pose. This evidence will be used to assess any need for possible changes to the legal framework in determining if there is a case to extend current regulations to reservoirs between 10,000 cubic metres and 25,000 cubic metres capacity. The research also considered options for risk designation and my officials will review the findings and engage with stakeholders in assessing whether changes are needed.

1 Under the Act and to an engineer MIOS actually means that if certain work is not carried out within certain timescales then the reservoir could become unsafe.

The attachment can be viewed online at: http://www.