Perhaps a lesser known feature of the original plans for the Midland Line was that the Midland Railway Company proposed a summit line over Arthurs Pass rather than the Otira Tunnel that we have today. The summit line would have run close to the current highway in a number of places and it incorporated gradients of up to 1 in 15 to achieve this.
Archives New Zealand have the drawings that were prepared of this proposed route dated 1899 which is probably the date that the Government received them from the liquidator of the Midland Railway Co, the company having been wound up after it failed to complete its contracted works. It had built the railway from “Brunnerton” (Brunner as we know it today) to Jackson on the western side of the route, but on the eastern side the line that had been started from Springfield was only complete to Otarama, with Tunnel 1 being completed but work yet to start on the Paterson Stream viaduct. There thus remained 92 km of very difficult railway through the Waimakariri Gorge and the Main Divide to be completed. The MRC sought a new contract in 1894 under which it would have undertaken to complete this section within a four year period but this was rejected by the government and eventually the works were resumed by the PWD. Otira was reached in 1900 from the western side, and on the eastern side, Otarama to Broken River was completed in 1906, Broken River to Cass in 1910, and Cass to Arthurs Pass in 1914. By that time the work was well in hand for the Otira Tunnel. This work was commenced in 1908 by the private firm of John McLean & Sons and was intended to be completed within four years. However at the time of expiry the company had completed less than half of the tunnel and the work was again taken over by PWD. Hole-through occurred in 1918. It was to be another three years before excavation and lining was completed, and in 1922 the rails were completely laid. The Midland Line was finally finished and opened to through traffic in 1923.
At the moment we have accessed drawings of the summit route from the top of Arthurs Pass down to Otira, approximately 6 miles. The below map shows the route coming down the Rolleston River valley with a big horseshoe curve and tunnel.
The route as shown with aerial photo background where it approaches the present day route.
By turning off the aerial photo background we can look at the contour curves with their heights marked in metres and gauge some idea of the way the railway climbed/descended. There does appear to be some sort of altitude markings on the drawings but we need to do some more work with these before using them. So at the moment we will go with the contour curves and what is marked on the drawings for gradients. At the bottom of the drawn section, 5 miles from the summit, the altitude is about 500 metres, while at 3 miles, it is 640 metres. This implies an average gradient of about 1 in 22 over that section. The gradients marked on the diagrams vary. From 3 miles the line is descending on 1 in 15 until just before the start of the tunnel, where the line levels out for the bridge over the Rolleston River (not marked). The tunnel itself is at 1 in 15 for a length of 1170 yards (1 km). At the bottom of the tunnel there is a longer level section which includes the bridge over Holts Creek (not marked) before a descent is resumed towards Otira at 1 in 15.
It will be interesting to put together the rest of the diagrams in the next few days to see what the line would have looked like as it came down from the summit and hopefully also the climb from Arthurs Pass up to the summit can be drawn in due course.