Monday 29 April 2019

Main North Line [0E]: Volume 10 Progress Report [4]

As we have reported in the last few posts in this series, we have been busy collecting aerial images for the Main North Line corridor from Christchurch to Picton and this work is now practically complete. Although a few extra downloads from Linz have been needed, most of the work has been completed and 150 GB of disk space was recovered by removing all of the download files that had been previously collected for the MNL corridor, which was the main object of this exercise. The majority of the work has been the effort needed to locate as many Retrolens aerial images of old stations as possible. 

Apart from the corridor surveys from NZR from the 1970s and a small number of dedicated station surveys, we have been fortunate to be able to draw on corridor surveys of State Highway 1, where it has been located close enough to the rail corridor, and since the earlier series of these date from 1961, it has been possible to capture many stations at an earlier time when they may have been open, and have closed by the time the NZR surveys were carried out.

Our knowledge of the Main North Line in Marlborough has been added to by discovering a previously undocumented series of realignments that were made on the former Picton Section prior to 1947/48 which in many cases is when the earliest historical aerial photos are available for the area. One of these is at Hog Swamp Creek just south of Seddon and is seen below.

We assume the key reason was to eliminate and bypass the bridge there, probably when it became due for replacement, as the curve was only slightly reduced in radius.

The next three photos show a series of realignments between Tuamarina and Para.

We don't have these mapped at present and it will be some time before we expect to draw these onto maps as probably mosaics will have to be made to enable them to be traced readily.

As one would expected some other useful discoveries have also been made along the way. 

Just north of Wharanui is the Waima River (previously known as the Ure River). Wharanui was the southernmost extent of the Picton Section, to which the line was opened in 1915. The section between Wharanui and Ward took four years to complete, which included 15 km of track, the No.3 tunnel (currently No.21 on the MNL and known colloquially as the Tar Barrel), and the bridge. This was the last single deck combined bridge on the Main North Line. To our best knowledge there were in fact only two single deck combined bridges on the whole of the MNL, the other one being at Parnassus and that was replaced about 1940. The road bridge at Clarence was originally intended to be a combined bridge, but in fact when the railway eventually reached Clarence in the early 1940s it got its own bridge. The double deck combined bridge at Seddon became rail only in the early 2000s when the new state highway bridge was built, but the redundant lower deck is expected to be reinstated for a cycleway.

Waima River combined bridge in 1969.

By 1972, work was starting to replace the bridge. It looks like the new railway bridge was built first.

By 1975 both new bridges had been built alongside the original. The highway originally crossed the railway on a one lane overbridge north of the river. This was replaced by a new overbridge south of the river, which took several more years to be built.

Another major river crossed in Marlborough is the Wairau between Spring Creek and Tuamarina. We understand there may have been some erroneous suggestions this was a combined bridge but that is not the case.

1937 aerial photo of the bridge. The highway at that time was some distance downstream and did not cross the river alongside the railway, as it does today.

This 1977 aerial shows work was underway to build a new curved railway bridge alongside the existing straight structure. Anecdotally we have heard the replacement was needed due to scouring of piers in the original but have not confirmed this. 

To conclude this post here is a 1986 view of the Awatere River double deck bridge just north of Seddon. There were a number of occasions that the road deck was closed for repairs (the bridge was built c.1902 and the deck was wooden) and generally, a temporary road was put through the riverbed as there was no convenient detour. The route of the most recent temporary highway on the upstream side of the bridge can be seen fairly clearly here (it was different from other occasions) and sealed highway in the riverbed, albeit on the downstream side, was still visible until the new highway bridge was built, after which it seems to have been dug up.