Preserving the Half Mile Pond at Longleat Safari Park

  • Project Reinforcing the dam at Half Mile Pond
  • Principal Contractor Land and Water Services LTD
  • Project Lead Andy Hember, Capital Sales
  • Key Benefit Using Sheet Piles to help preserve the idyllic Half Mile Pond, home to Hippopotamus’ and Sea Lions
Trench sheets at Longleat safari park


First opened in 1966 as the world’s first drive-through safari park outside Africa, Longleat Park is the UK’s number one safari park. Located at the east of Longleat House, the Half Mile Pond is a manmade structure built in the 1790s. As it is also classed as a reservoir, this requires ongoing prevention of flood risk. An impressive £2 million project was introduced in 2022 to help preserve and upgrade the reservoirs eighteenth century dam. It is one of many dams and reservoirs built by renowned landscape architect Lancelot Brown, whose nickname ‘capability’ stemmed from his habit of describing landscapes as having ‘great capabilities’.

Previous experience working with the customer meant that MGF were called in to help support the unique scheme with efforts starting in mid-October 2021.

As part of the scheme, the parks popular railway track was temporarily closed in October 2021. The railway track runs along part of the reservoir wall, allowing visitors an up-close view of the animals, so it is critical that it reopens in time for the Spring season so that visitors can continue to enjoy the attraction.

Trench sheets at Longleat
Trench sheets installed at Longleat
RHS 1 v2

The Solution

Due to the size of the reservoir, flood defence measures are necessary so that the water flow will not pass over the dam or affect the dam’s strength. The combination of ground pressure from the railway track along with movements caused within the dam from the 110,480 tonnes of water, has caused a build-up of pressure. As a result of this, measures put in place will move pressure from the water into one controllable area.  Despite an initial setback due to weather conditions in February pushing back scheduled installation as the team could not install the sheets safely or effectively in the rain, the rest of the project went ahead as planned.   

In total, 570 metres of GU13 Sheet Piles were required across the whole scheme. Brackets and timber cladding were incorporated into the design as a measurement guide so that eventually the earth can be brought up to the same level as the dam. Pontoons were floated on the lake to install the sheet piles safely, being careful not to disrupt the sea lions and hippopotamuses living in in the water.  

The scheme grew during construction so that sheet piles were now also required further down the railway track, extending the section of the reservoir being reinforced. The strengthening of the dam will also allow for additional locomotives to run along the railway line, making them more available for visitors.

The surrounding enclosures are dependent on the reservoir, as the gorillas need the wet land to safely separate their area from the rest of the park. Every part of the scheme has been co-ordinated with the safari team to help ensure the safety of those working on site as well as the animal’s continued welfare throughout ongoing construction.

Quick communication between MGF and the Longleat team allowed for speedy deliveries that met the parks accelerated time scale due to the need to reopen the railway track before Spring. The quick response time satisfied the customers’ requirements and allowed the scheme to continue without delay.

“MGF have been an integral part of the team and have supported the design engineers and contractors throughout the scheme. Longleat Estate are extremely grateful for their expertise and logistic support, for what has been a challenging project delivered within a tight timetable”

Jon Timney, Estate Director

Longleat safari
Longleat park
Trench sheets

The Verdict

Throughout the project, MGF had a close relationship to the park, engineers, and the Land & Water team onsite. This allowed for easy communication to ensure a quick and efficient service was provided so that tight deadlines were met.

Additional work is due in Winter 2022 to add wooden cladding to the sheets once the park is closed to help maintain a natural aesthetic, this is a big challenge for the team as they will again need to work alongside the animals living in the park to get everything done in time for the next season. 

To thank all those involved in the project, a plaque will be installed at either end of the reservoir with names engraved so that future visitors can be informed of the efforts made to the park that will help continue its ability to function and keep the animals living there happy and safe.  

The ongoing improvement of the park will help to bring in more tourism, ensuring the future of Longleat.