Unpermitted excavation on a flood storage reservoir
Publish date
02 September 2025
Case ID#
3268
Title
Unpermitted excavation on a flood storage reservoir
Nation
England
Regulator reference no.
537
Legal status
Statutory
Reservoir type
Impounding
Reservoir capacity
10 - 24,999m3
Year of construction
1970 - 1989
Main construction type
Earth fill embankment
Dam height
0 - 1.99 metres
Dam flood category
B
Hazard class
High-risk reservoir
Reservoir use
- Flood risk management
Owner type
Public body
Date & Time of incident
08 July 2024 - 12:00
Date incident closed
08 July 2024
Observations that caused the incident to be declared
- Other (including pollution and unplanned scour release)
Describe the incident
During routine maintenance works, the undertaker of a flood storage reservoir noticed that someone had excavated into the dam. A contractor working on behalf of a developer had removed a section of the bank. The undertaker notified the supervising engineer and investigated the cause. The undertaker and supervising engineer visited the contractor within 24 hours. They instructed them to stop all works and reconstruct the embankment. The reconstruction was completed under supervision of the supervising engineer. The available documents on the Local Planning Authority website did not make it clear what the exact approved details for works on the dam were. The Environment Agency had been formally consulted, and they had provided details of their required conditions. Work on site suggested the contractor was not aware of the required conditions. The situation appears to have occurred by a lack of suitable communication. The undertakers have since discussed with the planning authority: how the incident was able to occur what corrective actions should be taken measures to prevent a reoccurrence.
Supporting photos
Natural processes which initiated or contributed to the incident
- None
What were the main contributing factors to the incident occurring?
Dam factors
- None
External factors
- Other external factors (describe below)
Shortcomings
- Process or procedural shortcoming
What was the root cause of the incident?
Impacts on the reservoir
- External erosion
Supporting photos
Describe any human factors which influenced the incident
Rapid attendance of undertaker and SE to construction site and instruction to cease works, and reinstate bank.
Describe any instrumentation at the reservoir and how this was used in warning of the incident or providing monitoring during the incident
Not applicable
Was instrumentation effective leading up to and during the incident?
Not Applicable
Describe any assistance by external parties and impacts on the downstream population
None
Summary of studies or investigations undertaken
There are investigations ongoing to ascertain the cause of the incident. The initial investigation indicates either a failure in communication between the LPA and the EA (in relation to application and discharge of planning conditions) and the contractor working for the developer or failure by the contractor to comply with approved conditions.
Lesson 1
- Regulatory
Improved communication is required to ensure all aspects of any proposed development that might affect a reservoir dam are encompassed with relevant conditions attached to any planning permission granted. It is advisable to involve the Supervising Engineer into the consultation process by the undertaker for this purpose. A suitable monitoring process of the works after planning permission has been granted should be conducted by the undertaker to ensure all works comply with the approved details and conditions.