Dam Outlet Repair – Case Study

Client: Earl Percy Southern Estates

Project: Sherbourne Dam Outlet Repair

Scope: Backslope Stabilisation to Dam

At the beginning of 2020 – well before everybody’s lives were dramatically changed, we were contacted by a privately owned country estate in Surrey who were experiencing problems with dam stabilisation and they asked us to come up with a solution for them.

The problem was caused by increased traffic to commercial units on the land which was a disused farm. Because the road across the top of the existing dam was constructed of a thin layer of concrete, it had cracked due to the downstream batter being too steep and it was starting to slip away. This needed solving quickly as the road was now heavily used.

After our site visit, we came up with the solution which was to strengthen the existing piling by construction of two wing walls which supported the structure currently in place. The walls were formed using GU21 trench sheets which were driven with a vibrating piling hammer.

Having stripped the existing decaying vegetation (which can be seen in the photo below), we reconstructed it with a clay material and compacted it into position.


We then repeated the process along the entire stretch to provide stabilisation.

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Gabion baskets were then put in place over the top of the outlet structure to stop any vehicles from going over the edge.

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The challenges were not necessarily technical on this project – the biggest obstacle we had to manage was coordination of the local businesses and residential tenants who needed to retain access to their properties and places of work, so we provided a full time banksman. Even our very own illustrious leader acted as policewoman, sorry bankswoman, during the project – nobody was going to argue with Mrs P!



Working beneath tree canopies also proved challenging and was overcome by adjusting our methodology and machinery selection.

Fibre optic cable was also present on site which we re-routed for the duration of the project and then reinstated into its original mapped position once we were complete.

Having completed the project on time and in budget, we had an extremely satisfied client.

Terraqua Environmental Solutions – not just lakes!

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