Lake Dredge

In April 2022, we began the first dredge of Queen Pool in over 100 years, removing enough silt over nine months to fill Wembley Stadium to the top. Dredging is the removal of silt from bodies of water. Silt is fine grains of rock, smaller than sand, that build up over time. This usually accumulates around one-two cm a year, but during severe storms deposits can reach up to 20cm. The biggest threat comes from the lake’s significant build-up of silt: the water is currently only 30cm deep when it should be around two metres to support the existent ecosystem and the creatures who depend on it.

Land & Water is a leading wet civil engineering firm that maintains and enhances the UK's network of waterways and is helping us to dredge the 300,000 cubic metres of silt from the Queen Pool. Charlie Oakes, Project Manager at Land & Water says, “our chosen methodology is designed to protect the lake bed as much as possible during the dredging with several pieces of equipment being specifically commissioned for this project”.

 

Remo-voles

One of the first things that happened was moving the water voles (which is part of our Remo-Vole programme) to their new home across the lake along with the fish which were moved back in 2018 when the water level was lowered for work on the bridge and cascades. We worked with Ecologists to make sure that the moving of the voles followed the good practice set out in the water vole Conservation Handbook, and fully licensed by Natural England.

What happens during the dredge?

The project will be using a wet dredge technique. We have three diggers set on a floating platform which will move slowly across the full surface of the lake, dredging over the course of about nine months. Along with the diggers are six hoppers which go backwards and forwards, bringing the silt from the platform to land. This removed silt is being relocated up to Great Park, where we will be creating a landform (a hill or mound) over 16ha. This land will then be returned to grassland.

Did you know? We had a local competition to name our Hoppers with names such as ‘Reg who likes to Dredge’ and ‘Mallard’ being selected as finalists.

Who designed the new lakes?

In 1763, the 4th Duke of Marlborough commissioned Capability Brown to redesign the entire parklands to reflect the changing fashions. Brown’s vision was a huge change from the traditional formal gardens that had been popular amongst the wealthy families of England. He focused instead on the creation of natural landscapes, using brand-new construction techniques coming from the Industrial Revolution to bring his idyllic designs to life, ‘building’ rolling hills, wooded clumps, undulating lawns and vast lakes exactly the way he wanted them. While there were two bodies of water in the landscape, Brown’s plans were to make them much bigger.

How did he do it?

He first built a dam at the point where the river turned south to stop water getting into the excavations. The shape of the new lake was then created by hand: the sides were dug and packed down before barrow runs were installed. These runs were raised pathways with pulley systems powered by horse, mule or donkey that would haul the dug earth and rocks from the bottom in a wheelbarrow that was steered by a man. Once the lake had been shaped, the bottom was lined to make it waterproof with a mix of sand, clay and water. To compress and smooth this lining, Brown used a more traditional method: he employed flocks of sheep to walk back and forwards to ‘puddle’ the clay into the earth. Once the new basins were completed, it took about a year for the lakes to refill!

Why is it called the Queen Pool?

The lake to the east had originally been named Duchess’ Lake after the 1st Duchess who had created the pool in 1715. When the lake was extended by Brown, as well as going up the Grand Bridge, he also took the lake further east towards Woodstock, incorporating the Queen Pool, a small fish pool that was known to have been a favourite place of King Edward III’s wife Queen Philippa. While the pool was submerged, its name stuck and the new lake became known as Queen Pool.

The Dredge in numbers

3 Diggers – on a floating platform

6 Hoppers – bringing the silt to land

9 months – how long the dredge will take

300,000 Cubic Metres – of silt will be removed.

100 Acres of farmland – where the silt will be transferred and spread for drying

3 months – how long it will take to remove all the equipment once the dredge is complete.

 

Our team preparing for the Lake Dredge