HS2 Update, March 2022

HS2 Update, March 2022

The Chilterns Conservation Board is working to hold HS2 to account and to minimise the effects of its construction works on the Chilterns landscape.

Leather Lane Oak Trees

Almost a year ago, we reported our concerns that most of the mature oaks along Leather Lane would be removed to allow for HS2’s construction road, rail cutting and Leather Lane diversion.  Each individual oak tree represents a significant landscape and wildlife habitat feature. Local people have demonstrated the importance of the tree line for foraging bats including the rare Barbastelle.  Following interventions by the CCB, Chiltern Society, Buckinghamshire Council and local community groups, designers have been looking over the last year at options to amend the design for the Lane diversion, to reduce numbers of trees being removed.  Progress is being made, though local people, who have commissioned their own experts, still believe that more could be done.  We will provide further updates as news reaches us.

Tunnelling at Chalfont St Peter

The tunnel boring machines (TBMs) were to break through into the base of the Chalfont St Peter vent shaft just after Christmas.  However, HS2 Ltd has advised that both TBMs have been stopped.  Apparently they were going too fast and the vent shaft wasn’t ready for them!

During the Select Committee stage of the HS2 Bill, a number of local experts predicted that tunnelling rates quoted by HS2 were far too conservative.  They argued that a far greater length of tunnelling could be achieved, avoiding above ground impacts, without delay to the HS2 programme.  It appears these local experts might have been right.

Stopping the TBMs comes as a surprise, given that HS2 has previously asserted that the programme depends on continual progress of the TBMs and that they wouldn’t be stopped.  Perhaps if, for example, issues around tunnelling beneath the River Misbourne are discovered, the machines will be able to stop after all?

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Chalfont St Peter vent shaft east (Image from The Chiltern Society HS2 photo diary)

Tunnelling and the River Misbourne

We are grateful to our friends at the Chiltern Society for sharing correspondence with the Environment Agency in which they set out concerns over the impact of tunnelling on the River Misbourne at Chalfont St Peter and near Little Missenden.  It has long been suspected that the top two or three metres of each tunnel will break through unconsolidated fractured chalk.  We understand that this has now been confirmed.

Our concern is that vibrations caused by the TBMs through this unconsolidated chalk could cause settling and even disruption to the riverbed leading to loss of flow of one of our internationally rare chalk streams.  As the TBMs approach the River Misbourne, it will be important that any risks are avoided.

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Misbourne Bridge showing HS2 work (Photo: The Chiltern Society)

Other impacts on the River Misbourne

It is not just below ground where threats to the River Misbourne may occur.  In mid-February, following a weekend of heavy rain, a local resident sent us pictures of silt-laden water flowing down Bottom House Farm Lane towards the river.  As many will be aware, the Lane has been significantly altered to allow for future traffic to the vent shaft further up the lane.

Sedimentation is a real threat to the delicate ecosystems of our chalk streams so we are asking HS2 what might be done to improve or mitigate this situation.

We are grateful for information provided to us by local people regarding works that impact on the AONB and its valuable habitats.  This enables us to ask questions of HS2 Ltd and its contractors and, together with others, push for improvements to designs or works to mitigate damage.

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