WHAKAMARU HYDRO STATION
The Whakamaru Hydro Station is about 40km north of Taupō.
Construction of the Whakamaru Hydro Station and Hydro Dam began in 1949, and the station became operational in 1956.
It was one of nine hydro stations and eight hydro dams constructed on the Waikato River from the 1920s through to 1970, which now comprise the Waikato Hydro System operated by Mercury.
The Whakamaru Hydro Dam was built using 270,000 cubic metres of concrete and 1000 tonnes of reinforcing steel.
The dam has short penstocks connected to four Francis turbines inside the hydro station. The original turbines had an installed capacity of 26MW per unit and were delivered by the former Dominion Engineering (Canada), now part of ANDRITZ Hydro.
In 2017, after 61 years of service, the turbines, generators and governors at Whakamaru were replaced with modern equivalents.
ANDRITZ, GE and MBCentury were contracted to complete the four-year refurbishment project, which added another 5MW per unit, moving total installed capacity to 124MW.
The new Francis turbines are able to generate more energy from the same volume of water, moving the station’s average annual output to 515GWh, enough to power the equivalent of about 64,000 residential homes.
Whakamaru is the main switching station for upper Waikato generation and supplies the transmission system that leads north. This includes output from Mōkai Geothermal Station fed through the Whakamaru G4 switchyard.
The road across the dam will be closed to complete work on the Diversion Gate.
Diversion Gate testing
We are planning to test the Diversion Gate at Whakamaru as part of our consent requirements under the NZ Dam Safety Guidelines.
The Diversion Gate is a crucial piece of equipment allowing water to be redirected to protect people, infrastructure, property and the environment from floods events.
The test will ensure the Diversion Gate is reliable and can perform as expected during high water flows.
We have planned this work for October and November 2025. State Highway 30 across the dam will be closed between October 13-17, and then again November 17-21, from 8am-7pm.
Yes. There is a west-bound detour travelling through Wharepapa South, Arapuni, Pūtaruru and Tokoroa, then on to State Highway 32. The east-bound detour travels through Mokai, Tirohanga and connects to State Highway 1 where it passes over the Waikato River to State Highway 30.
We need to close both lanes, so we have enough room to safely manoeuvre the crane into place. During the work, divers will be in the water and may need to be as deep as 40m to help guide the stoplogs into place. A compression chamber will also be stationed at the top of the dam in case it is needed by the divers.
We have asked New Zealand Transport Agency to close the road for five days at a time, but we are hoping to complete the work in fewer days. We acknowledge closing the road will be frustrating for people who rely on the route to travel every day. We hope the advanced notice will give people some time to prepare and plan their journeys.
The work needs to be done during the day so our team can have optimal visibility when maneuvering the stoplogs into place in the river. Performing this task at night would be dangerous, and the health and safety of our team is paramount.
We have lots of experience performing maintenance projects on all of our hydro stations and dams on the Waikato River. It’s important work to make sure these assets are safe for our staff and safe for the communities they neighbour, and that they can continue to generate electricity. At the Karāpiro Hydro Dam, the road was closed for three years while an extensive rehabilitation project was completed on the hydro station. At the Arapuni Hydro Dam, in 2026, we will need to close the road across the dam for 18-26 months to carry out heaving maintenance work.
Watch this page for updates, you can also email our Hydro Stakeholder Manager Larnie Chrystall: Larnie.Chrystall@mercury.co.nz