Chilterns Conservation Board’s statement on the Little Missenden sink hole above the HS2 tunnelling operations

Chilterns Conservation Board’s statement on the Little Missenden sink hole above the HS2 tunnelling operations

The Chilterns Conservation Board (CCB) is alarmed by reports that a 6m wide and 5m deep sinkhole appeared above the route of HS2 tunnelling very near to Shardeloes Lake, near Little Missenden, on Saturday the 13th of May.


Chilterns ANOB

The CCB and others have warned for many years that the unstable nature of the fractured chalk meant that HS2 tunnelling operations might lead to long term permanent damage to the chalk aquifer, River Misbourne chalk stream, the wider landscape and wildlife living above the route.

For example, geologists, including Dr Haydon Bailey, highlighted their concerns over 13 years ago in a report published by the Chiltern Society in August 2010 – just six months after the government announced its preferred route for HS2. At the time, Dr Bailey’s report summarised potential impacts including:

  1. long term damage to the chalk aquifer;
  2. pollution of the main water supply system for the north western Home Counties area and potentially further into north London (a point emphasised by Dr Bailey when he appeared before the High Speed Rail Select Committee in July 2015);
  3. running the risk of serious ground collapse in areas with deep sections of weathered chalk;
  4. depressing the water table in the Misbourne valley, resulting in
    • the total loss of surface flow in the Misbourne River system, and
    • the destruction of the adjacent habitats
  5. the aesthetic loss of the Misbourne River and its replacement by a dry valley.

Clearly point 3, the serious ground collapse, has now occurred.

Despite confident assurances by HS2 Ltd throughout the Select Committee process proceeding approval of the HS2 Bill, and repeated assurances by their contractors since, the Chiltern Society, the Chilterns Chalk Stream Project, the Chilterns Conservation Board, and many local groups and individuals have continued to express their concern that tunnelling operations will be extremely damaging. Unfortunately, our fears appear to be justified and we will now be urgently seeking answers and for appropriate action to be put in place to safeguard the landscape, wildlife and residents of the AONB.

CCB and Buckinghamshire Council's Position Statement from May 2021

Read Chiltern Conservation Board and Buckinghamshire Council’s previous Position Statement on the impact of HS2 on the Chilterns’ chalk aquifer and its chalk streams (May 2021).

In particular, refer to point 4: ‘Not only is the chalk bedrock fractured, but the River Misbourne is “perched” – the river-bed is above the water table – and so is particularly fragile. As the TBMs (Tunnel Boring Machines) tunnel a mere 20m beneath the river at Chalfont St. Giles and Shardeloes Lake below Little Missenden, disturbance to the riverbed may cause water to drain away, leading to permanent damage to this rare chalk stream habitat and loss of wildlife


The Chilterns Conservation Board has been involved in the High Speed 2 (HS2) project extensively since it was first announced in 2010 and together with many other local groups and individuals, argued that the route should not pass through the protected landscape of the Chilterns AONB.

Although the Chilterns Conservation Board remains steadfast in its view that HS2 will have a significant and lasting negative impact on the Chilterns Area of Outstanding Natural Beauty, it continues to work with the HS2 Review Group and relevant partners to secure the best possible outcome for the environment despite the decision. Read more about our work over the last ten years via the link below.

Related news

HS2: more sinkholes open up in the Chilterns

We are aware of a further two sinkholes appearing in farmed fields between Sibley’s Coppice and Frith Hill.

Hyde Heath Sinkhole

We have been made aware of a second sinkhole occurring above one of the HS2 tunnel boring machines (TBMs) in Hyde Heath.

Chilterns Conservation Board’s position on the cancellation of the Northern Leg of High Speed 2

The announcement by the Prime Minister cancelling HS2 north of Birmingham undermines the justification for the remaining section of the route.

Chilterns ANOB
Chilterns ANOB

Challenging HS2

Find out how we are actively working to hold HS2 and their contractors to account, to reduce environmental damage and seek the best designs possible.
Chilterns ANOB

Chilterns AONB Boundary Review

We are are working closely with Natural England to explore the case for and against extending the boundary of the protected area of the Chilterns AONB. Find out about the project, and how this could benefit people and the landscape on our Boundary Review page.
Chilterns ANOB
Chilterns ANOB

The Management Plan for the Chilterns National Landscape

The Management Plan sets out the policies and actions to be followed by all stakeholders to conserve and enhance this special place. The current Plan (“the Chilterns AONB Management Plan 2019-24”) has been extended to March 2025 and is currently under review.
Chilterns ANOB

Keep in touch!

Sign up for our email newsletter to ensure you never miss out on news about our work in the Chilterns AONB.
Chilterns ANOB