Blenheim Palace Lake Dredge

Why are we dredging?

An important part of the Blenheim Palace World Heritage Site – Queen Pool has an ecosystem rich in nitrogen and phosphates which is ideal for a healthy marine population. It also attracts overwintering wading birds which have given this area its status of Site of Significant Scientific Importance.

Unfortunately, the levels of silt threaten this delicately balanced ecosystem:

• Its current depth is around 30cm when, for optimum health, it should be around two metres.
• The dredge will remove around 300,000 cubic metres of silt, supporting the future wellbeing of the lake’s inhabitants by returning Queen Pool to that ideal two metre depth.

What is a dredge?

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 at a rate of around 1-2cm a year, but during severe storms deposits can reach up to 20cm.

Queen Pool has been dredged twice before, to our knowledge: partially in 1840 and then fully in 1895-96 when the 9th Duke of Marlborough received the dowry from his marriage to Consuelo Vanderbilt.

We are performing a wet dredge to remove the silt in Queen Pool. This means that there is no need to drain the lake or lower the water level any further, as is the case with a dry dredge.

How are we protecting the inhabitants during the dredge?

We have an area management plan to reduce the impact of the dredge on the lake’s residents.

The fish were moved from the Queen Pool to the Great Lake when the water level was lowered for the work on the bridge and cascades in October 2018.

We have been relocating water voles and safeguarding the area for all local wildlife from Autumn 2021. You may have seen our Remo-voles traps around the edges of Queen Pool.

What happens during the dredge?

We are now using a wet dredge technique for Queen Pool.

We will 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 then transferred to an agreed site of 100 acres of farmland where it will be spread evenly for drying. This land will then be returned to grassland.

We will have to close part of the route of Queen Pool, so there will be a period of time when the ‘loop’ around Queen Pool won’t be accessible.

We will put up maps showing different walking routes, we will also add interpretation boards and updating our website so everyone is aware of what will be happening as the Dredge takes place.