Toddbrook Reservoir – What Went Wrong?

Two reports have now been completed into the cause of the failure of the slipway at Toddbrook Reservoir in Whaley Bridge on 1st August 2019:

  • The “Toddbrook Reservoir Independent Review Report” by Professor David Balmforth, commissioned by DEFRA; and
  • Report on the Nature and Root Cause of the Toddbrook Reservoir Auxiliary Spillway Failure on 1st August 2019” by Dr Andy Hughes, commissioned by the Canal & River Trust (CRT).

Both reports are publicly available on-line.  Whilst I don’t pretend to understand the technical details, both authors are quite clear that there were multiple serious defects in the original design of the spillway.  This enabled water to flow under the slabs forming the spillway, eroding the fill beneath them and, ultimately, displacing the slabs themselves.

Interestingly though, the authors differ in the significance of the contribution of widely-reported maintenance issues at the dam: Balmforth views this as another primary cause of the failure, whereas Hughes sees it as a very much a secondary consideration.  Balmforth also mentions a third contributing factor, the failure of the CRT to lower the water level when the severe weather warning was first issued; but is unable to judge if this could have prevented the outcome on the day.

Whilst Balmforth and Hughes are concerned with specific issues of dam design, the general pattern of multiple “latent incubating defects” in a system is very familiar from studies of previous disasters from Aberfan to the Challenger Space Shuttle.  As in these previous incidents, various people in various different organisations (and indeed members of the public in Whaley Bridge) were aware that there were issues with the dam, but nobody was able to put the pieces together: what Barry Turner called a “Failure of Foresight”.  Turner went on to identify four common features in such failures, two of which are specifically highlighted again in the reports into Toddbrook Reservoir:

  • Division of responsibilities – both organisationally between CRT and DEFRA, and individually between Supervising Engineers and Inspecting Engineers; and
  • Poor intra/inter organisational communications – in particular people not having access to drawings and other documents that they needed, and the failure of the most recent Inspecting Engineer’s report to prompt urgent remedial action on the slipway.

Reflecting on the incident at Toddbrook Reservoir, if we can identify and address these sorts of problems in our own organisations then we are one step closer to preventing a disaster closer to home.

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