Legend has it that a Scots-NI link is a waste of money

This proposed tunnel between Scotland and Northern Ireland (“NI link ‘will be a tunnel’” LTT 20 Mar) is a romantic project – setting the skills of 21st century tunnelling engineers against the aspirations of Finn McCool who, in antiquity, allegedly built a Causeway from County Antrim to the Isle of Staffa in the Scottish Hebrides, only to later rip it up. 

The North Channel between Portpatrick and Larne is about the same width as the Channel between Dover and Calais, so it is tempting to draw comparisons! However, looking at the depths of water shows a huge difference – right in the middle of the North Channel is a deep rift called Beaufort’s Dyke which has a depth of over 1,000 feet, more than four times deeper than the English Channel above that tunnel. The Dyke is amongst the deepest waters on the continental shelf – and it is also about three miles wide.

Assuming any such tunnel would be an electric rail tunnel with suitable gradients it is easy to see that the tunnel length could exceed 40 miles – much longer than the Channel Tunnel. It could be amusing to compare the relative ‘benefits’ of the two tunnels using the made-up formula:    

B = P1 x P2 / L2

Where: 

- B is the benefit of the link

- P1 & P2 are the populations at each end of the link     - L is the link length 

Using the very approximate figures in the table below:

P1 P2   L

(million) (million) (miles)

Channel Tunnel   50  500 30 

NI / Scottish Tunnel   5  50 40 

The ‘Benefit’ for the Channel Tunnel would come out as:

50 x 500/ 900   = 27.8

The ‘Benefit’ for The Irish/Scottish tunnel would come out as:

5 x 50 /1600 = 0.156

Perhaps we can learn from Finn’s mistake!