Saturday, 10 April 2010

South Island Main Trunk, Dunedin-Palmerston, Part 2: The Route

OK, here’s part 2 of this series, and here we look at the route with the help of Google Maps.

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The above is an actual Google map rather than overlaying Google Maps with a KML file like I have often done. However, you can still get the KML file for this map and enjoy the superior functionality and detail of Google Earth by going to the NZ Railmaps website (Blog Maps).
The aim of this post is to detail significant features and what I know about them, between Dunedin and Palmerston. To do that, we’ll zoom in on bits of the map as we go along.

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The first bit of detail going north from Dunedin is the deviation at Pelichet Bay. This used to be an actual coastal bay in Dunedin and there used to be a station there. The green line shows roughly where the original railway route might have been and the round symbol is roughly where the station might have been. At a guess Parry St is roughly the route. When the railway was originally constructed, I believe that it followed the shoreline. Later on, a causeway deviation was built and the land in between was reclaimed. Since then there has been a lot more reclamation. The land where the line used to go was about where the South Seas Exhibition of 1925 was held – and that’s the year that the deviation was opened, apparently. Now that site is where Dunedin’s new World Cup stadium is being built. The causeway was opened as a double track, but before then, the main line from Dunedin to Pelichet Bay station was doubled around 1908.

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Getting a bit further north from Dunedin there were a number of shorter sections where the line wound in and out of the bays, following the shoreline of the time. Causeways were built to straighten, flatten and double the line in these areas also, but the bays were not reclaimed. NZRTA4 says that the first causeway was opened in 1931. We don’t have any readily accessible information on the curves and gradients of the original route, but it’s a reasonable assumption from the road that now follows the shore that curves were sharp and grades in places were steep by rail standards. So we can comfortably assume that there was a three part improvement in operating conditions.

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This map shows the longest causeway, over 1 km across two bays, which took the line into Sawyers Bay station. At its northern end a new 313 metre double track tunnel was dug beneath the suburb of Roseneath, replacing an earlier 103 metre tunnel. There is no obvious trace of the older tunnel today, and as a road follows the original railway route, it would be a reasonable assumption that the tunnel could have been demolished to make way for the road. As my previous post about double track in Dunedin notes, NZRTA4 raises a question mark over whether this double track causeway ever had the second track laid. The tunnel is dated 1939 and the deviation was opened for traffic in 1948.

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North of Sawyers Bay is about where the ability to make further improvements to the railway got a lot more difficult and expensive. I remember reading somewhere that a proposed solution was to put in a big tunnel between Sawyers Bay and Waitati to overcome the grades and curves. As the straight line distance between the two places is about 9 km, this would have been a pretty difficult and expensive project. Obviously it would never have got high enough up the priority list and today it will never likely happen because there is not enough traffic on the route to justify it. Sawyers Bay-Merton may be an unfortunate bottleneck, but the road is not really much faster so it is tolerable in the same way as the Dashwood Pass is tolerated on the Main North Line. In the railwaymania era there probably would have been deviations built but the likelihood of such things today is pretty small.
What was possible and necessary in the difficult 45 km section between Sawyers Bay and Merton has mainly focused around four of the five tunnels. Going north, the first of these is the No. 6 daylighted in 1971. After that you have the No.5 Mihiwaka Tunnel, and the work here has been mainly driven by necessity, needing to strengthen and repair the tunnel’s lining because of ground movement. There have been clearance problems here at times, too. I don’t know whether there are any long term plans at present for further improvements here, or whether the clearance issues currently pose any limitations for the type of freight than can be carried on the line. The most recent works done in the tunnel were just last year, a Dunedin firm cut out sections of the original bluestone wall/ceiling lining and replaced it with concrete. Repairs to this tunnel are a pretty regular event and must have driven the proposals for a new tunnel years back but I know nothing more about whether more significant work is on Ontrack’s list. The Cliffs Tunnel No.4 is an interesting one that I don’t know very much about at the moment. I have heard a story that there was not a tunnel here originally, that the tunnel was put through to bypass a difficult dangerous cliff face section. The photographs tend to support a contention that the track might once have gone around the side of the tunnel. Apart from  that I don’t know any more about it.

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The last of the four tunnels, No.3 is much more interesting; it is the notorious Puketeraki Tunnel.  This was built as 157 metres in length and was an original feature of the line. The area through which it passes is the same area where Seacliff Lunatic Asylum was built and where State Highway 1 passes over the “Kilmog”. It is all well known as an area of unstable land that has caused lots of problems over many years. The Puketeraki had years of work done on it before the Railways decided in the mid 1930s that they’d had enough and that they would put the track around the side of it. But this has led to a very sharp curve which I guess could be only 130 metres in radius, and trains have to go fairly slowly through it. However in the area curves around 140-150 metres are often seen and the grades tend to limit train speed anyway. The tunnel can still be seen today, particularly at the northern end where there is a distinct embankment approaching the clearly visible portal.
In between Tunnels 3 and 4 the line takes a long curving route around the coastline at Waitati, and this is the intermediate stage between the twin peaks of the Sawyers Bay-Merton route. Just north of Merton is a bridge across the Waikoauiti River then a long straight, flat approach to the eponymous township with its well known racecourse. About three years ago SH1 was deviated to the west of the township, bypassing a level crossing within the urban limits and also redundancing the highway overbridge at Tumai, though it remains in use for local access. There are one or two places where curves have been eased before the line enters Palmerston on a north-south alignment, turning north-east to run alongside the highway through the town.
The main map also shows the Dunback and Makareao Branches. This is largely as an interest factor in Palmerston, although on my trip I did take a walk along the first straight, this was limited by the fact the train only stopped for a little over half an hour. If we had been there longer I could have had a closer look at the line right up to where it crossed over State Highway 85.
Part 3 of this series is a little way off yet as I still have a lot of work to do on the photo album for this trip. Stay tuned…