River Chess Association Meeting

We have been in consultation with the HS2 and the Environment Agency for some years about the potential damage that could be done to the chalk aquifer that supplies the water for the River Misbourne and River Chess. As part of the project HS2 plan to drill two tunnels and a number of ventilation/access shafts through the chalk, we are concerned that this work will damage the aquifer through pollution or blocking the migration route of the water that feeds our rivers. This could result in the loss of these rare iconic rivers and the habitat and wildlife they support. The Government identified this risk and in 2016 issued a financial indemnity worth up to £70 million to Affinity Water for the loss of their water source from the aquifer as a result of this work. HS2 have agreed to attend a meeting to give us a presentation on how they intend to mitigate the risks to our rivers.


  1. Overview - David McCann (HS2)
  2. Geology - Gareth Jones (Align)
  3. Tunneling Methodology - Jacques Didier (Align)

Notes on the talks


The River Chess Association organised a very well attended meeting with HS2 managers, Engineers and Geologists from Align JV (the Tunnelling contractor) and Environment Agency representatives. In the course of the meeting it became clear that although more Ground Investigations are needed, the contractors have no doubt that the tunnel can be constructed as proposed. However, it is also clear that the possibility of damage to the aquifer, and interference with the Misbourne and Chess water flows cannot be completely excluded – which is why Affinity Water have an indemnity of up to £70m to cover any expenses in case they have to find alternative water sources.

Other users of the rivers were well represented in the audience, and pointed out that their requests for similar treatment had been turned down, during the parliamentary select committee hearings.

One positive fact to emerge was that the Tunnel Boring Machines will shut down automatically, in the event of unexpected changes of pressure at the cutting heads – largely to comply with Health and Safety requirements. There will be meetings twice daily to consider progress, and data will be shared with the Environment Agency.

On the other hand, it is clear that despite drilling over 100 boreholes at 200m intervals, the structure of the aquifer is not well understood. The Environment Agency have to approve the final design, but it seems likely that they will at best impose some conditions on the contractors.

Post construction, monitoring of the rivers will be ongoing, possibly for a further 10 years. However, there was no mention about what could be done to restore water flows, if they are found to have been affected.