Wellington Taps Wainuiomata for Water

In 1878, Wellington experienced severe water shortages, despite having just spent £80,000 on their water supply. The water flow was stopped at night, extraordinary usage was charged for and fines introduced for wastage. There were devastating fires at the Princess Hotel and the railway station that couldn’t be extinguished. The city needed to find more water.

The Wellington City Engineer James Baird identified Wainuiomata as a new source –  Wellington rainfall averaged 1,200 millimetres per annum, Wainuiomata 1,900 millimetres.

Baird recommended damming the Wainuiomata River in Sinclair Valley. The council and ratepayers agreed. Pipes were ordered from Glasgow and tenders let for two pipe tunnels in 1880. Work commenced in 1881 and was sufficiently advanced by September 1883 for the water mains to be charged.

The dam consisted of a concrete wall with earth filling and a spillway. The impounded water flowed through a concrete headrace, 1.9 kilometres long, to a pressure-reducing well. Here it dropped 18 metres to enter a 750-millimetre cast-iron pipeline. This pipeline passed through two tunnels to reach Gracefield then proceeded along the Petone Esplanade and Hutt Road to Thorndon Quay.

The project was beset by problems. Transporting the pipes to the site was difficult and flooding caused damage during construction. On the night of 19 October 1883, after a fortnight’s heavy rain, waters scoured out the earth filling behind the dam, opening a large gap between it and the rock core below. Repairs to this nine-metre gash were hindered by another flood in November. And in January 1884 – on the day the city planned to turn on Wainuiomata’s water overnight floodwaters rose to above the dam crest. The dam was washed away along with all the bridges downstream. The damage took months to repair and the water didn’t flow to Wellington until May.

Wainui 1884
Damaged reservoir 1884 (Ref: PA-f-036-13-2, ATL)

Three years later the Wainuiomata dam was back in the news when the mains were turned off for repairs. Another disastrous fire occurred for which the flow from the Karori reservoir was inadequate to extinguish. There was a public backlash and a bitter public spat between Baird and the new City Engineer, Bernard Loughrey, over the scheme as a whole. The media lampooned the leakiness and frequent inspection visits. However a review of the scheme concluded that it was sound and had added significantly to the quality and quantity of Wellington’s water supply.

Wainui Water
Brown, Thompson & Company (Ref. B-034-020, ATL)

In the 1890s confidence in the abundance of the Wainuiomata supply led to over-use. The public were prohibited from filling swimming pools and watering gardens to conserve supply for domestic use. A  water inspector was appointed to monitor things. 

The flow of water was reduced as the pipes became encrusted. City Engineer, Richard Rounthwaite, was instructed to find ways to increase supply. Rounthwaite recommended new dams in the upper Wainuiomata and above the Karori dam. Test bores were sunk at the Wainuiomata site and ratepayers approved a loan for the project in 1905.

The council turned its attention to Wainuiomata after completing the Karori dam. The site was upstream of the first Wainui dam beside a hillock called Solomons Knob. The river had to be diverted and new roads and bridges built before dam building could start. Work was completed in November 1911.

Morton NZG_19100914_p0017_i001_b
NZ Graphic, 14 September, 1910

The new dam, named after city engineer William Morton, was made from reinforced concrete and was 164 metres in length and 12.5 metres high, and contained 485 million litres of water.

Morton recommended duplicating the 600-millimetre main from Gracefield to Wellington – this pipeline had frequently leaked and burst, particularly on the Wellington fault along the Hutt Road. In March 1907 a major flood of the Hutt River destroyed part of the pipe bridge, breaking the Wainuiomata main.

A new pipe bridge over the Hutt River estuary was built in 1909 and a duplicate main, connecting to the city’s reticulation at Thorndon Quay, was started in 1910. This reached Thorndon in 1912 and increased the supply of water from Wainuiomata by 1,075 million litres in its first year.

pipe bridge
AP Godber, Pipe bridge on the Hutt River, 1910 ( APG 0453-1/2-G, ATL)

However Wellington wasn’t done with tapping the area and in 1915 Morton recommended that the Orongorongo also be used for the city’s water supply. The Orongorongo River had been identified as a source in the 1880s. Work began here in the 1920s.

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