NORPLAN suggest low-cost alternative to proposed Harris surface link
Norway-based underground construction experts NORPLAN estimate that a tunnel between Berneray and Harris should cost £50 - £70 million all inclusive, based on similar tunnelling projects in Norway.
In August last year, design consultants Jacobs Babtie published a feasibility study commissioned by Comhairle nan Eilean Siar examining different link options. It proposes a causeway and bridge link costing a projected £57-£75.5 million.
Such a link is likely to bisect Scotland’s first proposed Coastal and Marine National Park.
‘Many Norwegian sub-sea tunnels have been built for well under £5 million per km,’ says Richard Duncumb, Divisional Director of Underground Construction Technology for NORPLAN, the ‘largest centre of hard-rock tunnelling expertise in Norway’.
‘It’s exceptional for hard rock tunnels in Norway to cost more than 100 million Kroner [approx. £8.5 million] per km.’ He adds that labour and materials are cheaper in the UK.
The 124 page report by Jacobs Babtie dismissed the idea of a tunnel in 4 paragraphs on p72, claiming costs would be ‘approaching £1000 million.’
This is 14 to 20 times NORPLAN’s more pessimistic cost predictions.
The report also forecasts an additional yearly operation cost of £0.7 million per km: a total of £6.65 million per year.
Richard is baffled by this. ‘Yearly figures typical for maintenance of Norwegian tunnels have been in the range of £30 – 50,000 per kilometre - which is 15 times less than Jacobs Babtie’s estimate.’ Half of this is typically electricity for lighting, ventilation and pumping.
The tunnel line would be through Lewisian Gneiss: a rock Richard claims is ideal. ‘What is their basis for claiming a tunnel in the Hebrides in geology basically similar to Norway’s will be fourteen or more times the price?’
NORPLAN would happily be involved in developing a Sound of Harris tunnel. ‘We are interested in working on the project, but obviously that would be in competition with others.’
He suggests a two-week ‘pre-feasibility study’ costing around £10 000 to locate tunnel portal sites and verify geology on the ground. Should this go to plan, it would precede a full study including detailed geophysical and geological surveys.
Norwegians are world leaders in tunnelling the kind of hard rocks found beneath the Western isles, with over 1000km of road tunnels; 95km of them sub-sea.
The longest is 25km long.
‘I don’t think there’s any other country that’s bored quite so many tunnels,’ says Richard. ‘Norwegian experience is that tunnels are regularly the cheapest option. Exceptions are with very short crossings, very bad ground conditions, or where the water depth is so great a tunnel would be disproportionately long to maintain acceptable gradients.
‘From an initial look at the information available, the Sound of Harris looks very promising. I’d be very surprised if there are major problems. Its depth is modest. Norwegian road tunnels have been bored more than 200 m below sea level.
‘I imagine a Norwegian contractor building such a tunnel would want to maximise use of local manpower and resources,’ he says, ‘importing a small number of specialist staff to supervise.
‘Parts of Norway are more remote than the Hebrides: I wouldn’t anticipate a problem there. A tunnel of this type would normally be constructed by conventional drill-and blast, with no need to import expensive machines.’
But hard rock is a problem, isn’t it?
‘Absolutely not. The stronger the rock the better: you can save a lot of money on tunnel support. The figures I gave are based on a degree of rock support being necessary. In some Norwegian tunnels, they just drill and blast - and that’s it, with virtually no permanent support of the tunnel rock required.’
Is leaking a problem in sub-sea tunnels?
‘Not at all. As with any tunnel you get a certain amount of ground water, which is pumped out. There’s never been a major uncontrolled water ingress in a sub-sea tunnel in Norway. Statistically, Norwegian tunnels are safer than the roads outside.’
Can the excavated rock be used as aggregate?
‘Blasted hard rock from tunnels makes good road embankments, and can be graded. Its value would depend on local markets.’
A 9.5km circular section tunnel 8m wide could theoretically produce well over a million tons. Current aggregate prices would give this a value of several £million.
So why does Richard think Jacobs Babtie’s estimates are so different from NORPLAN’s?
‘Possibly because of relatively little recent experience of hard rock tunnelling in Britain. A different technology is involved in the soft ground of much of the UK. There is perhaps an assumption you need the same support in hard rock as soft.
‘It seems to me that a tunnel’s been dismissed without good grounds, which I can’t understand Jacobs-Babtie doing. I’d assume it was an omission, rather than anything deliberate.’
Page 6 of the Jacobs Babtie report states that the depth of the current study is constrained by a ‘lack of site-specific information’ - making it interesting to speculate how some of the conclusions arrived at or implied in the report have been reached.
Combined with the report’s list of recommendations, this suggests NORPLAN’s proposed £10 000 pre-feasibility study could be considerably more detailed and specific. ‘If we find rocks similar to Norway,’ Richard Duncumb says, ‘we could then refer to numerous similar tunnels built in similar conditions.’
Given the increased erosion and wave action noted since the Berneray and Eriskay causeways, the Jacobs Babtie report raises important questions regarding a surface link’s effect on offshore sediment and water movements, and also ecological effects (amongst other things the Sound is an important spawning ground).
The report seems to imply some impacts will be fully known only when a link is built, while recommending a raft of costly and lengthy impact studies.
A tunnel could sidestep both the uncertainty and the need for most of these studies.
Additionally, as Richard Duncumb says, ‘seas and weather are irrelevant for a tunnel’. An affordable surface link would use causeways similar to theEriskay causeway, which was storm-damaged shortly after completion.
Given the Jacobs Babtie report’s stated concerns regarding climate change and the need for renewable power generation, it seems ironic that its preferred option is the most vulnerable to predicted storm and sea-level increases.
And while an option for a high bridge allowing passage through the Stanton Channel is suggested (elevating costs to the report’s high estimate of £75.5 million), shipping freedom in the Sound would still be lost.
‘If decision makers are interested,’ says Richard Duncumb, ‘we could arrange visits here for people to get a feel of what we do first hand. If the Council were interested, we could come and give a presentation.’
In view of what might be gained – namely a cheaper, less vulnerable, low maintenance all-weather crossing with minimal or zero visual, environmental, shipping or fishing impact, which would be immune from weather and tide, allow more flexible renewable energy options, last for centuries, and generate valuable road aggregate - a tunnel surely deserves more than (according to the people who should know best) a wildly inaccurate few lines in a report which could dictate the future shape of the Western Isles.
On the face of it, NORPLAN’s proposed pre-feasibility study could be the best £10 000 the Comhairle ever spent. If it’s not seriously looked into, many will want to know why.
An informative 30-page report by the Norwegian Public Roads Administration, ‘Subsea Road Tunnels in Norway’ is available at: http://svvgw.vegvesen.no/http://svvbibsys01.vegvesen.no/epublisher/document.asp?func=show&id=513&type=0&service=0
Jacobs Babtie’s report can be viewed at: http://angusnicolson.blogspot.com/2006/09/berneray-to-harris.html
NORPLAN can be contacted via their web site at www.norplan.com
Both Comhairle Eilean Siar and Jacobs Babtie are invited to reply to this piece and NORPLAN’s suggestions. Their replies will be covered in next month’s issue.
The Hidden Link
Part of the Jacobs Babtie report’s favoured proposal for a Sound of Harris surface link is a tidal and wind power generation scheme to help recoup capital costs. The report suggests this would bring the estimated total initial outlay to £127-£145 million.
For an alternative scenario involving retaining the existing ferry, the report estimates capital costs of developing renewable energy sources in the Sound of Harris (presumably at a smaller scale) at £13.66 million.
Added to a tunnel this would mean an expected initial outlay of no more than £84 million while apparently generating a similar order of return over 50 years.
However, the nature of the connection between a road link and renewable energy generation implied by the report is perhaps surprising.
The link is described as providing tide-based power generation opportunities the report itself describes as less tested and economically viable than alternatives. Surely a poor bet, then, if the aim is to recoup capital? It also notes that better marine generation opportunities lie to the west. Additionally, some designs of tide and wave generator work best in open water. Given the relative success of existing open-water tidal schemes (e.g. Devon’s Lynmouth turbine) the connection between a surface link and tidal power seems tenuous at best.
On p66 the report admits retaining the existing ferry link would provide ‘more open’ scope for renewable energy opportunities, as these would be unconstrained by the location of the transport link or the need to integrate the two.
It anticipates a surface link will cut cable laying costs for the proposed wind turbines, while facilitating maintenance. Perhaps surprisingly, this would be by boat, gangway or bridge, suggesting the turbines will be sited at a distance from the causeway - possibly for safety legislative reasons.
‘The physical link,’ says the report, ‘may also be seen as a means of encompassing the renewables potential of the Uists into the grid upgrade [...] currently proposed to link only Harris and Lewis to the Mainland’.
According to both the report and NORPLAN, a tunnel can carry a cable as easily as a causeway.
In another passage, the report states:
‘This [a fixed transport link also joining the Uists to the upgraded Harris/Lewis electrical circuit] could offer the possibility of renewables expansion in the southern isles in the absence of specific reinforcement of the existing Loch Carnan link to Skye.’
For better or worse, this leads to the conclusion that any fixed link will mean wind factories in the Uists. Given likely economic pressures to maximise use of the Lewis-mainland grid link planned for Lewis’ proposed wind power schemes, it seems naïve to assume these will be small-scale.
This link, it seems, is as much about renewables expansion in the Western Isles as facilitating travel.