Seepage from voids in masonry and tree roots
Publish date
02 September 2025
Case ID#
3116
Title
Seepage from voids in masonry and tree roots
Nation
England
Regulator reference no.
305
Legal status
Statutory
Reservoir type
Impounding
Reservoir capacity
25,000 - 99,999m3
Year of construction
< 1800
Main construction type
Earth fill embankment
Dam height
2 - 4.99 metres
Dam flood category
D
Hazard class
High-risk reservoir
Reservoir use
- Other
Owner type
Private individual(s)
Date & Time of incident
05 July 2006 - 12:00
Date incident closed
Observations that caused the incident to be declared
- Leakage or seepage from a new leakage point
Describe the incident
The owner of the reservoir noticed leakage passing around the outlet structure at the toe of the embankment. The reservoir level was lowered by pumping water over the crest. Leakage through the masonry wall forming the upstream face of the dam and through the sides of the drop shaft on the line of the dam crest had been occurring for many years. Drilling was carried out vertically from the dam crest and from within the spillway drop shaft to fill voids and stem the leakage. The voids behind the drop shaft wall, possibly together with rotten tree roots within the embankment, probably contributed to the new seepage path developing between the drop shaft and the downstream toe.
Supporting photos
Natural processes which initiated or contributed to the incident
- None
What were the main contributing factors to the incident occurring?
Dam factors
- Other dam factors (describe below)
External factors
- Damage by trees (tree fall, instability, etc.)
- Other external factors (describe below)
Shortcomings
- Maintenance shortcoming
What was the root cause of the incident?
Impacts on the reservoir
- Internal erosion (fill deterioration)
Supporting photos
Describe any human factors which influenced the incident
Daily surveillance and prompt reporting of this incident to the Supervising Engineer, together with a precautionary drawdown of the reservoir, prevented the incident from resulting in a dam break.
Describe any instrumentation at the reservoir and how this was used in warning of the incident or providing monitoring during the incident
None present
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
Vertical drilling into the masonry wall and horizontal drilling into the embankment fill were undertaken to establish where water was flowing through the wall.
Lesson 1
- Emergency response
- Operation and maintenance
- Surveillance and Monitoring
Daily surveillance and prompt reporting of this incident to the Supervising Engineer, together with a precautionary drawdown of the reservoir, prevented the incident from resulting in a dam break.
Earlier grouting works around the drop shaft may have prevented the incident arising.
Lesson 2
- Emergency response
Pumps should have been used from the outset rather than siphons. This may have allowed earlier completion of the remedial works.