Thursday, 3 January 2013

On the Otago Central trail [2]

I have now completed detailing the map and am preparing to generate page views for the map document. For the meantime I am starting with the Cromwell end because of the work I have done here to determine where the line went, this will be published as an interim release of the map as the rest of it will take another day or so to finish. Here for now are the 15 images for the mapping of the Cromwell Gorge, because this is a substantial point of interest with the significant changes due to building the hydro dam and raising the Clutha River through Cromwell Gorge.
It should be noted that the below is an interpretation of maps and GE coverage and the exact route of the railway today is uncertain because of large scale changes in the Cromwell Gorge associated with the hydro development. For this reason the purported rail route is marked as, “Inexact Route”. However just because the highway alignment today is similar to what it was back in 1980 doesn’t mean that the bulk of the rail route is out of the water. There are one or two particular places where this is in fact the case and they are near Cromwell. For the rest of the route, most of it would be under water today, or buried by construction works associated with the dam.
It is generally documented and accepted that the highway was taken further up the side of the gorge and therefore the lower formation of the highway was abandoned with the railway alongside. There has been some speculation, particularly in a TV programme, that this means some rail remains could be found below the waterline. However, Dangerfield & Emerson states “nothing remains west of Clyde” although I believe there are a couple of pieces of formation still out of the water. It is important to note as well that there was large scale contouring of the gorge sides below the waterline in various places throughout the Gorge which was necessary to stabilise numerous landslips that exist throughout the Gorge. These works would have buried or destroyed any remnants of the railway line. I wouldn’t rule out some remains may exist but because of all of the earthmoving work done for the hydro development, which was a lot more than at most hydro sites, a lot will have disappeared.
Earlier in the week I did post in this same article my belief that the highway was simply higher on its existing site. This has proved to be a mistaken view. The railway formation is laterally displaced from the current highway by perhaps 100 metres in some places and at a lower level. Therefore rather than saying it is all buried under the highway, it is more correct to say that it is either underwater or buried under dam construction works. The NZMS1 maps show that the highway in the 1960s appeared similar to the current highway. In retrospect it is very difficult to see a 100 metre difference on a 1:63360 map, which at that scale would be of the order of 2 mm. The highway would appear similar because it still follows similar contours of the land. On the other hand the maps I have drawn are depicted at a scale of 1:6000 and it is possible to show what will be a significant change of location at such a scale. Therefore I am going to redraw the maps in the knowledge that the railway line is significantly displaced but this will not be easy to do, so it will never be more than an approximation.
The original maps with this article are temporarily withdrawn until the new maps have been assembled.