Mohaka Viaduct

Mohaka viaduct
The Mohaka viaduct crossing the Mohaka River in Northern Hawke's Bay, New Zealand
Coordinates	39°04′07″S 177°07′33″E / 39.0686°S 177.1257°E / -39.0686; 177.1257Coordinates: 39°04′07″S 177°07′33″E / 39.0686°S 177.1257°E / -39.0686; 177.1257
Carries	Single track of the Palmerston North–Gisborne Line (mothballed 2012)
Crosses	Mohaka River
Locale	Raupunga, Northern Hawke’s Bay, North Island, New Zealand
Owner	ONTRACK (New Zealand Railways Corporation)
Characteristics
Design	Plate girder
Material	Mild steel
Total length	276.8 metres (908 ft)
Height	95 metres (312 ft)
No. of spans	12
History
Designer	John L. Cull and W. L. Newnham
Engineering design by	Components prefabricated by PWD workshops, Mt Maunganui, Bay of Plenty
Constructed by	The Public Works Department (PWD) for the New Zealand Railways Department (NZR).
Construction begin	1930
Construction end	June 1937
Opened	1 July 1937

The Mohaka Viaduct is a railway viaduct spanning the Mohaka River in northern Hawke’s Bay, on the East Coast of the North Island of New Zealand, near the small settlement of Raupunga. It was built between 1930 and 1937 by the Public Works Department (PWD) for the New Zealand Railways Department (NZR). It is 276.8 metres (908 ft) in length, and at 95 metres (312 ft), is the tallest viaduct in Australasia.

Construction of the railway line from Palmerston North to Gisborne line began in 1872, connecting Palmerston North with Napier in 1891. The northern portion from Napier to Wairoa, and thence to Gisborne followed much later, being built between 1912 and 1942. The section of line between Napier and Wairoa passed through difficult country, requiring heavy earthworks, five tunnels, five high steel viaducts to cross deep gorges, and numerous other bridges. Progress was slow, with portions of the line being progressively opened as sections were completed and handed over to the Railways Department.

After completion of the line from Wairoa to the viaduct site in late 1930, the pre-fabricated steel work was railed from the small port of Waikokopu, about 40 km east of Wairoa. A start was made with the driving of test piles, and the digging of 18.3 metres (60 ft) to 21.3 metres (70 ft) deep foundations in the river bed, enabled by the use of pressurised caissons.

However, the Government of the day faced major financial problems following the in the USA, and the onset of what would become the Great Depression of the 1930s. To cut costs work was suspended on most of the line, although foundation work continued at the Mohaka viaduct.