Erosion during overflowing from water flowing over piles and onto embankment
Publish date
02 September 2025
Case ID#
3119
Title
Erosion during overflowing from water flowing over piles and onto embankment
Nation
England
Regulator reference no.
309
Legal status
Statutory
Reservoir type
Non-impounding
Reservoir capacity
10 - 24,999m3
Year of construction
1950 - 1969
Main construction type
Earth fill embankment
Dam height
5 - 9.99 metres
Dam flood category
A
Hazard class
High-risk reservoir
Reservoir use
- Other
Owner type
Public body
Date & Time of incident
26 June 2007 - 12:00
Date incident closed
Observations that caused the incident to be declared
- Dam or embankment overflowing or overtopping
Describe the incident
In one case, a flood storage reservoir overflowed because its capacity was exceeded. In the other, a river overflowed the defences surrounding it and water flowed into the adjacent flood storage reservoir. In both cases, the embankments had been raised with steel sheet piles. When the water overflowed the sheet piles it dropped vertically onto the earth embankment below causing erosion.
Supporting photos
Natural processes which initiated or contributed to the incident
What were the main contributing factors to the incident occurring?
Dam factors
- Deterioration of materials
External factors
- None
Shortcomings
- No apparent 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
Describe any instrumentation at the reservoir and how this was used in warning of the incident or providing monitoring during the incident
There is no instrumentation.
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
The cause of the damage is known. It will be appropriate to carry out localised site investigations (trial pitting) to determine the length of the piles and whether or not water has passed through or beneath them. Investigations should also be carried out to determine the extent of previously reported corrosion of the piles. The remedial scheme must take into account that overtopping of sheet piles in the crest of an earth embankment causes erosion and a suitable design detail should be engineered to ensure that, when the remediation measures are completed, it does not happen again. The undertaker should look at other of their sites where there are sheet piles driven into earth embankments and satisfy themselves of their integrity against damage from overtopping.