Wainuiomata WTW

New Zealand

This project was designed for Wellington Regional Council, with MWH Global NZ acting as consultants.

Raw water to the treatment plant is extracted from both the Orongorongo and Wainuiomata rivers. The Orongorongo system comprises intake structures on the Orongorongo River, Big Huia and Little Huia Streams. This water is transported to the Wainuiomata treatment plant by means of a 5.6km long pipeline and tunnel, where a series of pressure reducing valves have been installed just upstream of the water treatment plant intake. 

The turbine generator are located in a purpose built structure adjacent to the existing pressure reducing valves. Under normal operation the turbine will take all of the water treatment plant flow, with the valves being retained for periods when the turbine is out of service for any reason.

Under favourable weather and water demand conditions the turbine could be expected to operate for as long a six months without any need to shutdown.

The plant operation will be entirely automatic with plant condition being monitored from the water treatment facility control room, which is located about 150m away from the turbine building. The control room is manned 8hrs a day, with a continuously manned call-out roster. Inspections of the turbine generator facility are envisaged to occur at most once per week.

The turbine generator works in parallel to the grid.



  • Gilkes 15" HCTI Twin Jet
  • Leroy Somer 353kVA 415 Synchronous Generator
  • CPS Turbine Control/MCCB panel (380kW 400v)
  • Shipped to Wellington Port ready to be transported to site

Key Stats

  • Commissioned May 2011
  • Power 318 kW
  • Net Head 83 m
  • Flow 463 l/s
  • Turbine 15" Twin Jet Turgo