16 April 2008

A Cook Strait tunnel?

You may or may not find this hard to believe, but I was pondering the idea of a tunnel under Cook Strait the other day. When I did the usual follow-up, plugging the words 'Cook Strait tunnel' into a well-known search engine, I found absolutely nothing. Well, there was this quick discussion on Public Address System, which is a good headline but nothing more. This spurred me into action. So, for no good reason other than to fill a void and secure my place in blogging posterity as (possibly, sort of) the first poster on the topic, here's a brief discussion of the prospects for a Cook Strait tunnel.

It's often mentioned that New Zealand has a similar land area to that of the United Kingdom, the country from which many Pakeha colonists originated. New Zealand has a land area of 268,000 sq km and the UK has 241,500 sq km. While the UK does have the outlying territory of Northern Ireland over the Irish Sea, most of the land area of the UK is easily accessible by road or rail. However, New Zealand is an archipelago split by Cook Strait and Foveaux Strait, which hampers communications and commerce and generally makes getting about a real nuisance. In my years living in Wellington I certainly bemoaned the lack of driving opportunities from the capital – it’s north or nothing – and the car ferries to Picton in the South Island are expensive.

Another island archipelago nation is Japan (land area 374,750 sq km), which is divided amongst four main islands. Japan has the advantages of having relatively narrow channels between its three southern islands, Honshu, Kyushu and Shikoku, and the considerable wealth required to connect those islands. Even the broad Tsugaru Strait between Honshu and the northern island of Hokkaido has been conquered by the 53km Seikan Tunnel, 23km of which is underwater.

New Zealand’s Cook Strait is the major break point in the New Zealand economy and the transportation network. On days with foul weather and high winds – and there are many of those days – ferries are held in port and aircraft are grounded, thereby shutting down the only links between the North and South Islands. The cost to business and travellers alike is high.

So I started wondering: has anyone seriously considered a Cook Strait Tunnel? Obviously it would be ridiculously expensive, perhaps beyond the ability of a small country to afford. But in practical terms, is it a workable proposition? The factors to be considered are distance, depth, geology and cost.


On this front, it’s good news! In theory, that is. Tunnels far longer than the width of Cook Strait have been in operation for years. The shortest distance across the Strait is about 22km from Cape Terawhiti on the North Island to Perano Head on Arapawa Island in the Marlborough Sounds at the top of the South Island.

When we look for examples in other countries, there are several tunnels longer than 22km. The Seikan Tunnel, mentioned above, tops the list. Next is the most well-known to New Zealanders: the Channel Tunnel linking England and France, which has a total length of 50km, of which 39km is underwater. This list shows seven tunnels – six rail tunnels and one road tunnel – longer than the 22km between Terawhiti and Perano.


Cook Strait has an average depth of 128m. Surveyors charting a course for the Saikan Tunnel found that the western neck of Tsugaru Strait had a maximum depth of 140m, so they sited the tunnel there. The English Channel is much shallower at its narrowest crossing though – only 45 to 60m deep. One consolation is that it’s certainly possible – the admittedly much shorter Eiksund road tunnel in Norway is the deepest undersea tunnel, reaching a depth of 287m below mean sea level at its deepest point. So a Cook Strait tunnel might have to be built at the cutting edge of engineering technology.


Here I’m on shaky ground, if you’ll excuse the pun. I can draw a straight line from A to B, but I can’t tell you whether the intervening material that has to be drilled through is good or bad. Given the environment of the strait itself, I can't imagine the rocks underneath it will be particularly easy to tunnel through. Not a particularly substantive analysis is it? Perhaps one of these bods might know something.


There's another factor that makes a Cook Strait tunnel quite challenging. While the narrowest crossing point is 22km wide, the topography of the terrain on either side of the strait is particularly rugged. If a rail tunnel to the South Island was considered, extending the Wellington railhead from the Thorndon station westwards to the coast would take the rail lines up steep slopes to residential Karori (which could certainly do with some livening up, but perhaps not from a busy freight line) and on through hilly terrain that would require numerous tunnels to pierce the ridgelines, which are aligned southwest to northeast.

On the other side of the strait it's just as tricky. Arapawa Island has the same steep hills to negotiate, and it would also require a tunnel or bridge across the Tory Channel to reach the South Island railhead at Picton. Blimey. Oh well, here's a nice picture anyway.


Okay, here's where the idea falls down. I suspect this will only ever be affordable in the far distant future when silver-suited engineers will lazily instruct a cyborg drill monster to go away and dig the tunnel, leaving them in peace to carry on the crossword in the digital Dominion Post.


I think as a result of this investigation into the prospects for a tunnel under Cook Strait the only thing we can be certain about is that I wouldn't have made a good engineer.

But don't get me started on the idea of a Cook Strait bridge... now that's an idea with potential!



Alastair said...

Aren't there a number of active fault lines that run through the Cook Strait? Surely that can't be a good thing for a tunnel.

The idea might work for unmanned freight trains but I wouldn't suggest putting people down there.

eT said...

Fault lines in Cook Strait? But that means we've built our centre of government right on them! Whose dumb idea was that?! I bet it was an engineer... ;)

Ken said...

It comes down to cost and given our population it probably isn't feasible ?

Having said that there are several options we could consider if the cost can be justified. An alternative to a bored tunnel could be a submerged structure sitting on the sea bed. These would be prefabricated sections made elsewhere then transported and sunk into place.

As I understand it, one major obstacle is a deep trench on the North Island side. One idea is to bridge that trench and then go down to a submerged tunnel beyond. This method could also deal with any seismic activity by mounting on isolater bearings, as is done with the Houses of Parliament.

The approach work you've already identitifed as another major obstacle and these alone would represent a major portion of the overall cost. It would be better if both road and rail capable and not subject to tolls.

Will de Cleene said...

Gday ET, ta for the compliment. Yeah, there's at least five faultlines (up to 20?) through Cook Strait. As the links in my post describe, so what. It's possible.

Alastair, I'm against dedicated trains due to both NZers love of their cars and that fact the rail would have nowhere to link to. NZ's main trunk line is useless narrow gauge and there's a wiggle in it (Raurimu Spiral) that makes bullet trains impractical.

eT said...

What were we saying about a bridge? See today's Guardian:

'The world's longest sea bridge was formally opened yesterday linking Shanghai to the industrial city of Ningbo across Hangzhou Bay in China. The 22-mile bridge will reduce the driving distance between the eastern side of Shanghai and the port town of Ningbo by 75 miles'

(22 miles is 35km in new money)


Gerard said...

One of the stated side effects of all those fault lines (SH1 out of Wellington runs along one!) is the fact that the two islands are moving apart. Not overly quickly, but they are.
The Power cable ("tether") between the two islands already has to cope with this.

Also, I believe most/all Japanese rail is also narrow gauge.

But trains would go against our national love of cars!

Ted from NZ said...

In all of your comments you have forgotten one factor against any sort of link bar a tunnel (n/a due to fault lines) which is the weather. One extreme was when I flew across cook strait in a cherokee November 2008 and it was like glass, the other extreme, well who can remember the Wahine in 1968? Not me because that was the year I was born, but I met an old guy when tramping in the Urewera's who was on the same life raft as the captain, and his car and all his hunting gear is now at the bottom of the strait.

EF said...

I have also pondered about a rail tunnel or bridge given that rail transport I am sure will become New Zealand's primary mode of transport in the future. We simply need to look at Europe and the ascent of rail transport there, to see that both the car and the plane are inferior to the speed, practicality and cost of train travel. While planes are limited by practicality, cost and security and automobile travel will be limited by safety and speed, a high speed train service linking the country on a new rail network will link our country in ways the plane and car will never achieve.

A tunnel across Cook Strait would be the center piece of this rail network and link our islands together into one land rather than the split archipelago that it is today.

The practicality and economics of the tunnel will hopefully be resolved by time and technology.

Anonymous said...

You should look at the many undersea tunnel in Norway, they are a good example. I have been there. It shows it can be done there for only a few thousand islanders and in some cases only a few hundred.

I think the cost of a road tunnel will depend on the amount of traffic. One car every 5 minutes or 5 car per minute makes a difference.
You dont have to look at the cost of the English Channel tunnel because you cannot compere the amout of traffic.

A rail tunnel makes no sense because of the terrible state of the railway lines in NZ. You cannot compaire NZ railways with the ones in Europe or Japan.

Ethan Tucker said...

Yeah, when I was in Iceland a few years ago I remember being impressed that a tiny country could build the Hvalfjörður tunnel to cross a fjord north of Reykjavik in 7 minutes instead of an hour (it's 5.7km long and 165m at its deepest point). Of course Iceland is considerably more wealthy per head of population than NZ, but it showed what is possible.

I think on balance a rail-only system would be easier to manage, safety-wise, and it would be easier to drill than a dual rail/road tunnel. True, NZ railways cannot compare with those in wealthier countries at the moment, but I think a Cook Strait crossing would provide a huge boost to the effectiveness of the rail network while at the same time reducing the environmental impact of heavy goods vehicles.

Anonymous said...

A rail tunnel would not be easier to build because a road can be build at a much steeper angle, the train tunnel would be much longer than a road tunnel.

Trains would only run few times a day witch means long waiting times.
Loading and unloading takes time and is labour intensive.
Where in Wellington is space to build a terminal?
My advice keep it simple like in Norway.
Think more of a better version of the Homer tunnel with a good asphalt road and forget a high-tech-future-world tunnel.

And what would be the cost of a modern railway line from Christchurch to Auckland?
Even with speeds up to 250km/h
it would take many hours.
So people would still use air transport.

Fraight transport could continue to use a ferry or use the tunnel in off-peak periods

Zydaine said...

Hey Guys, I have actually sat around thinking about this for a while myself too, and I think it would be a great idea.

Yeh there are faultlines running throught the strait and that got me researching. There is actually a undersea Rail Tunnel currently under construction which will conect both parts of Istanbul (capital of Turkey). The tunnel, known as the Marmaray tunnel, will run across the Bosphorus strait, which seperates Europe from Asia. I realise the tunnel will only be 1.8km, but it is still an example of an underwater tunnel running across active faultlines. They are using earthquake-proof immersed tubes to build it. The tunnel, once completed, will also be the world's deepest undersea rail Tunnel.

If we look at the Seikan Tunnel, the Channel Tunnel and the above Marmaray Tunnel, we can see that it is most probably posible to do.

We would also, probably, need to hire the Japanese to engineer this project (just like the Turks did).

However, our current train system ain't the best. Auckland will have new Electric trains in 3 years, but they will most probably still be outdated compared to other nations rail systems. We could probably consider a nation-wide rail system consisting of both underground and aboveground railways (like the system in england - mainly london).

Zydaine said...
This comment has been removed by the author.
Anonymous said...

This is how the Cook Strait Tunnel could look like (copy&paiste)


Anonymous said...

What about a flying fox wire which could carry cars, a bit like a gondola; this would be a very cheap alternative to a bridge or tunnel. 20km isn't very far, a few poles drilled into the strait could provide adequate stabilty for the wire...

Anonymous said...

Has anyone considered a floating tunnel? That is a hollow tube - immersed in the water - that is would float to the surface but which is pulled down by chains connected to a cable. It would be rather like an inverted suspension bridge.

Anonymous said...

A brige would be far more productive in the long run, while a tunnel could end up being limiting. A bridge is also easier to maintain and far more appreciable as an engineering marvel!

Anonymous said...

Umm Cook Strait might be an average of 128 m but I believe there is a bloody great canyon running down the middle of it that is substantually deeper... oh and bit's of it fall down in earthquakes too.

Anonymous said...

I think you miss the point about road vs rail. Road will inevitably become over loaded and will be inefficient as a people goods mover. Rail with decent terminals each end will be able to load efficiently. Don't get hung up on the rest of the rail net work. The tunnel will be its own entity. The rest will catch up in time. A rail tunnel would generally be narrower electric trains won't need exhaust emission extraction and probably less safety considerations.

Clive Carter said...

A road tunnel would likely to be ruled out of the question for the same good reasons it was considered and dismissed for the English Chanel tunnel (risk of accidents; extra cost for ventilation, fire, inefficency etc.)

The more practical rail tunnel could invigorate rail throughout the north and south islands.

It may be decades before its built, but it should be built, knowing full well that at some point in the future, it would become subject to an earthquake.

Elfin-Saftee would object on risk grounds. However, any quake big enough to damage the tunnel (and possibly risk lives in it) is going to cause far more damage in nearby Wellington, yet no one has yet proposed shutting down the capital due to this risk.

There is risk everywhere at all times. It can be managed and minimised.

A rail tunnel could be designed and constructed so as to be earthquake resistant (not earthquake proof). Engineers are some of the most creative minds around and this is a purely technical problem to be addressed.

At some point in the next 200 years, an earthquake may damage the tunnel. Is it worth forgoing all the economic advantages of a fast, continuous, 24/7 all-weather link for that risk?

I suggest not!