Tawa Flat tunnel unlocks capital
Construction of the Tawa Flat rail tunnel and deviation during the early 1930s opened up Wellington’s expanding northern suburbs and the area beyond while ushering in a new era of engineering technology.
Hemmed in by its steep hills, the capital had begun to slowly breath after the completion in 1886 of seven tunnels along the rail line to Johnsonville, which was then the rail route north.
But that tedious trip was replaced in the 1930s by the current main line route through to Tawa Flat, via the longest double-track tunnel in New Zealand.
Engineers employed machines used for the first time in domestic tunnelling, including a cement gun and a pneumatic pick known as a ‘‘mucker’’ that gouged out loosened soil and dropped it back into wooden tip trucks hauled by electric locomotives.
The muckers were described by The Evening Post on March 23, 1929, as ‘‘marvellously compact yet tremendously powerful’’.
The Post heralded the building of the £2.05 million ($236 million now) 11-kilometre deviation as opening up ‘‘a vista of greatly increased passenger and freight facilities for the Port of Wellington’’.
‘‘The complete combined scheme, which includes the new railway yard, in which will be incorporated the Thorndon sea wall and reclamation, provides for a central railway station, linked up with the ferry service.’’
Part of the connective tissue of the city, tunnels have played a crucial role in Wellington’s tricky expansion.
The Karori tunnel was completed in 1900 and in 1907, the Hataitai and Seatoun tram tunnels helped the suburbs move south and east.
The slopes of Northland were opened up in the 1920s by the Northland tunnel and with the automobile age came the Mt Victoria tunnel in 1931 and the motorway tunnel under The Terrace in 1978.
Tawa was relatively sparsely populated in the 1930s, but its population recently passed 15,000.
It is served by the five suburban passenger railway stations of Kenepuru, Linden, Tawa, Redwood and Takapu Road, with a significant number of commuters travelling daily by train into the Wellington CBD to work.
Tawa Flat tunnel under construction in the early 1930s.