The waters of Lake Mahinerangi — whether still and sparkling in summer or grey and forbidding in winter — hide many of Waipori’s secrets. Beneath these waters lie the remains of the town and the evidence of decades of hard work by miners.
Living under a threat
Early miners harnessed the flow of the Waipori River to provide water for sluicing, powering dredges and producing energy for mining activities such as pumping. Other people saw the river’s potential too, and the river that was so important for miners ultimately led to Waipori’s demise.
In 1902 a group of businessmen formed a company to dam the Waipori River further downstream from the town, to generate electricity to power gold dredges and supply business and residential customers in Dunedin and the surrounding district.
Waipori Falls, some distance from Waipori township, was the spot with potential for hydroelectric power generation. Here the river descends rapidly through a gorge, creating sufficient head to power generators.
The Dunedin City Corporation (now the Dunedin City Council) didn’t like the idea of private enterprise being behind a utility company, so arranged for an act of parliament in 1904 to enable it to compulsorily acquire the Waipori Falls Electric Power Company.
The first hydroelectric station was built at Waipori Falls in 1907 and produced 2 MW of power. This posed no threat to the goldfields and town further upstream, but this station was the beginning of a series of developments that finally saw the end of the Waipori community and goldfield.
The beginning of the end
Demand for electricity continued to increase and it was soon apparent that the Waipori power scheme would have to be expanded. To start with, new dams were built on tributaries to the Waipori River to create extra storage capacity.
Then an earlier idea to build a higher dam and flood the Waipori Flats was resurrected, on the condition that an investigation showed that the remaining mining potential of the area was not great enough to outweigh the benefits of increased electricity generation. An investigation in 1918–1919 showed that the value of the gold to be covered by the new lake was not sufficient to prevent the construction of a higher dam that would flood the flats.
Acts of parliament were passed in 1920 and 1924 to give Dunedin City Corporation the right to build higher dams and flood the Waipori Flats, despite staunch opposition from runholders, miners and other residents. Existing mining claims were allowed to be worked out, but no new claims could be lodged.
The Dunedin City Corporation bought out the mining rights and plant of three miners and started building an 11.6-metre high dam approximately 1.1km upstream from the original weir at Waipori Falls. This was to flood the Waipori River flat to create Lake Mahinerangi, and bring about the end of Waipori town and much of the mining.
The day a town was closed down
In March 1924 a conference was held at Waipori to negotiate compensation claims for the land and other property that was to be submerged under the new Lake Mahinerangi. Mines Department officials, the mayor and other council officials from Dunedin and the local MP convened with about 30 residents, landowners and miners.
Over two days of long but generally good-natured discussion, compensation claims were settled. Tuesday 25 March 1924 was called ‘Settlement Day’ for the town.
By September a newspaper reported that the town was all but deserted, while a few miners lived in the area continuing with their claims. One, John Thomas Johnson, was specifically named in the empowering legislation as being allowed to continue taking water for sluicing and to continue mining.
(Evening Star 22 September 1924)
The lake kept rising
Because of poor ground conditions at the site of the dam built in 1924, it was decided that this dam couldn’t be further raised as first envisaged. Instead, to generate even more electricity a second dam, known today as the Mahinerangi Dam, was built a short distance downstream in 1931. This was constructed in stages; first to a height of 20.4 m (67 feet) and then raised to its present height of 34 m (112 feet) above the river bed in 1946, submerging the upstream dam.
By 1949 the lake had filled to its present level. John Thomas Johnson had to give up the last gold operation in the Waipori district.
The power scheme grows
Though the lake level wasn’t raised further after 1949, the power scheme was developed further over subsequent decades.
Two further dams and power stations were constructed downstream from the original 1907 power station in the 1950s. The original power station was completely replaced on a new site just upstream during the 1960s and 1970s.
In 1981, the Mahinerangi Dam power station was completely replaced with a new power station, intake tower in the lake and tunnel through the right embankment of the dam. A tunnel through the Lammerlaw Range was also constructed at this time, diverting water from Deep Stream into Lake Mahinerangi.
In 2008, two additional power stations were built on the Deep Stream diversion to utilise the flow and significant head between the tunnel outlet and Lake Mahinerangi. The Waipori scheme was fully automated by 1997.
In 2011, the Waipori hydro scheme was augmented by power from the newly developed Stage 1 Mahinerangi wind farm on the north western slopes above Lake Mahinerangi, bringing the total combined average annual output of the Waipori scheme to 280 GWh. That’s 140,000 times the output of the original power station.
Beneath the lake
Though the remains of the township are well hidden below the lake, sometimes the water level drops to reveal some of Waipori’s secrets.
This 2008 photo shows the site of the house of Robert and Margaret Cotton. Just before the lake was formed the house was moved onto higher ground, but over decades became neglected and was eventually demolished. On the original site the water tank stand, garden paths and some foundations are visible whenever the lake level drops significantly.