Waiau Branch Bridges: Research Notes

As part of the work of drawing the Waiau Branch, research was undertaken using Archives New Zealand files to locate and detail the branch’s 33 or more bridges. Les Dew’s book “The Great Northern” was also drawn upon as a source, although it contains some errors. For example, it states that there were 32 bridges on the line (p.106, top left corner). Whilst there were in fact bridges numbered from 1 to 32 by the time the line closed, this only reflects the number of bridges that were in existence at the time the numbering sequence was created. There are a couple of anomalies in bridge numbering that can be picked up from studying the bridge files in more depth. Firstly, bridges on the line were originally numbered in the Main North Line sequence, with the later Bridge 1 originally being MNL Bridge 43, and later Bridge 32 originally being possibly MNL Bridge 65. If these numbers are correct, about 9 other bridges were added in between the two sequences being created. Any other bridges that had been removed by the time the Waiau Branch bridge sequence was created would only have had MNL bridge numbers and would not have been filed under the Waiau Branch. An example of this is the 33rd bridge implied by the first sentence of this post. That is the Weka Pass viaduct, which was replaced by a culvert in the 1930s.

Here is a list of the bridges, starting with the less notable ones. The length details have 2 numbers referring to the number of spans and their length in feet (more than one time if several different span lengths were employed) and the material details have two descriptions, the superstructure and the substructure. Although some of the bridges were rebuilt with steel spans, the majority retained wooden components throughout their lives which kept bridge carpenters busy up until closure.

The more notable bridges will be referred to in a separate list following the first one. Refer to the published maps of the line to locate them.

  • Weka Pass viaduct: see below.
  • Bridge 1: Weka Stream, 7m 37 ch. 1/20′ steel/concrete. The only bridge on the Weka Pass Railway.
  • Bridge 2: Overhead bridge 12.1 km. 3/? wood/wood. After many years of use this was demolished recently.
  • Bridge 3: 9 m 64 ch. 1/14′ wood/concrete.
  • Bridge 4: 9 m 72 ch. 1/25′ steel/wood
  • Bridge 5: 10 m 46 ch. 2/25′
  • Bridge 6: 10 m 60 ch. 2/21’8″ steel/concrete.
  • Bridge 7: 13 m 39 ch. 1/?
  • Bridge 8: 13 m 59 ch. 2/20′ steel/concrete
  • Bridge 9: Washpen Stream. 13 m 71 ch. 3/25′ steel/concrete.
  • Bridge 10: 14 m 62 ch. 1/12′ wood/concrete.
  • Bridge 11: 14 m 75 ch. 1/12′ wood/concrete.
  • Bridge 12: 15 m 44 ch. 1/12′ wood/concrete.
  • Bridge 13: see below.
  • Bridge 14: 16 m 20 ch or 26.1574 km. 2/11′ & 6/13′ wood/wood.
  • Bridge 15: see below.
  • Bridge 16: 21 m 77 ch. 1/14′ wood/concrete.
  • Bridge 17: 22 m 16 ch. 1/12′ wood/concrete.
  • Bridge 18: Dry Creek. 23 m 74 ch or 38.5119 km. 8/13′ wood/wood.
  • Bridge 19: 26 m 24 ch.1/14′ wood/concrete.
  • Bridge 20: see below.
  • Bridge 21: 26 m 64 ch or 43.1433 km. 1/13′ wood/concrete.
  • Bridge 22: School Creek. 28 m 54 ch or 46.1581 km. 4/? steel/concrete.
  • Bridge 23: 29 m 27 ch. 2/15′ wood/concrete.
  • Bridge 24: 30 m 63 ch. 1/12′ wood/concrete.
  • Bridge 25: 31 m 5 ch. 1/12′ wood/concrete.
  • Bridge 26: 31 m 39 ch. 1/12′ wood/concrete.
  • Bridge 27: 32 m 9 ch. 1/16′ wood/concrete.
  • Bridge 28: 32 m 28 ch. 1/12′ wood/concrete.
  • Bridge 29: 35 m 58 ch. 2/12’6″ concrete/concrete.
  • Bridge 30: 36 m 47 ch. 3/12′ concrete/concrete.
  • Bridge 31: 37 m 66 ch. 3/20′ steel/concrete.
  • Bridge 32: 39 m 75 ch. 3/20′ steel/concrete.
  • Waiau River bridge (not formally part of Waiau Branch): see below.

The five most significant bridges were:

  • Bridge 42 MNL, no Waiau sequence number. Weka Pass viaduct near the 10 km peg. As this was not researched this time around, no other info is documented.
  • Bridge 13: Waitohi River. 15 m 58 ch. Its probable MNL number was Bridge 50 (uncertain). In the 1930s after a major rebuilding this consisted of 22 spans each 25′ length steel joists on wooden substructure. If it was a different length when originally built this information has not yet been documented.
  • Bridge 15: Hurunui River. 18 m 42 ch or 29.49 km. Dew refers to the original construction details being 2/8′ and 40/40′ Howe Truss spans. By the mid 1970s the bridge apparently had been partly rebuilt at the south end with beam spans (as visible in aerial photos). These appeared to be about 20′ long and covered approximately one third of the total length so there would have been about 27 of them. The two thirds of the bridge from the northern end could have been covered by 27 of the 40′ truss spans. This has not been formally confirmed in any documentation to date. NZR advertisements calling tenders for removal in the early 1980s state a length of 496 metres.
  • Bridge 20: Pahau River. 26 m 34 ch or 43.1433 km. Original details unclear but one file reference states it was 29/40′ truss so possibly similar superstructure to the Hurunui. Rebuilt in 1902 as 3/8′ & 78/15′ beam spans, it was described in NZR advertisements calling for removal tenders in the early 1980s as being 364 metres in length. Dew states one of the end spans was replaced by an embankment in 1916. Several times the possibility of substantially shortening the bridge, a section of which crossed dry riverbed, was considered (for as much as 550 feet on one occasion) but never implemented.
  • Waiau River bridge, Waiau. If the railway had proceeded beyond Waiau, as would have been the case if it had been continued as the Main North Line, it may have shared a bridge with the inland highway at this location. A bridge was built across the Waiau River in 1883 but it is unclear if there was ever any thought of it being designed for use by a future railway although this is suggested in Dew at p.222 (by contrast, the Waiau River bridge closer to the coast at Parnassus was a combined structure opened in 1912 for the then Cheviot Branch and remained so until 1940 when a new rail bridge was built alongside). The old wooden bridge at Waiau was replaced in 1965 by the present single lane concrete structure.

As this list makes clear, many of the bridges were tiny. On aerial photos, the 12′ ones are practically indistinguishable from the numerous culverts that followed a similar design (a lot of culverts were pipes under the track, but some of perhaps the early ones were beams on abutments just like the single span bridges). Dew shows a picture of a “bridge” with masonry abutments but this is believed to be a culvert, so technically there were no bridges with dressed stone abutments or piers and in fact the practice is virtually unknown in Canterbury (compared to Otago). Given the differences between the MNL and WB bridge sequence numbers, many small bridges were either added after the line opened or were reclassified from culverts. Another anomaly from Dew is that all the existing bridges between 1 and 13 were rebuilt with steel joists on concrete piers in 1930. Documentation sighted this time around suggests only a few bridges in what was then the MNL 43-50 sequence were proposed and completed to this plan, including Bridges 1, 6, 8, 9 and 13.

Now that you are all bored to death of reading bridge statistics here are a few photos from Patrick Dunford (or other photographers as marked).

Captions will show when the mouse is hovered over an image. The last two images are a bridge and a culvert near Medbury that look almost identical. What was the exact difference?