Unpermitted excavation on a flood storage reservoir

On two occasions at a large, washland flood storage reservoir, a third party (utilities and highways companies) excavated into a dam crest. A public road runs along the crest. One incident involved installation of a water main under the road. without the knowledge of the undertaker. The other incident involved?constructing a reinforced concrete structure under the public highway. Both occurred without the knowledge of the undertaker. The risk to the dam was that during construction, the integrity of the dam was compromised. The works had temporarily discontinued the site. If a flood event had occurred, increased erosion may have happened at the site. A bigger risk for reservoir safety would be if the contractors did not reinstate the bank to a standard appropriate for a water-retaining structure. In each event, the undertaker became aware of the works and they escalated it within the undertakers organisation. There was no evidence found that the works had a suitable permit or planning permission. The undertaker engaged with the organisations responsible for the works. They ensured that a QCE was consulted on the remaining works and reinstatement of the dam. Investigations are ongoing. The investigation aims to understand how construction works could occur on the crest of the dam without the knowledge of the undertaker. The undertaker aims to find out if there had been involvement of the local planning authority, or the Environment Agency permitting process.

Engagement of the local communities, farmers and other third parties to actively report any issues they observe is encouraged and was the primary source of the issues covered by these two incidents.

There is no instrumentation at the reservoir. It is doubtful whether the incident could have been identified by conventional instrumentation. The Undertakers staff visit the reservoir at regular intervals, there is a local Internal Drainage Board that has pumping assets associated with the reservoir, both within and external to it, who visit those assets regularly and report any issues they see with the dam or Cradge bank.

On the morning of 4 January, a member of the public reported the incident. The public provided aerial drone imagery.

Seepage is still being monitored and stopped when the water levels in the adjacent river dropped to their normal range. The two breaches were investigated and the cause of the failure identified, for each, as being the result of piping between badger excavations on opposing faces of the cradge bank. Each breach was repaired under the supervision of a QCE when suitable access had been arranged and the reservoir drained of all retained water that entered through the breach.