Scheme Operation
The Opuha scheme operates by releasing stored water from Lake Opuha via the dam into the Opuha River, which flows into the Opihi River.
Water released from the dam ensures the viability of the river system, while also allowing for the take of irrigation water for the Levels Plain, Kakahu, Totara Valley, and Sutherlands irrigation sub-schemes via distribution races and channels. Water is pumped from these races and channels by landowners. Some irrigators pump directly from the rivers either through galleries or adjacent bores. None of the schemes use borderdyke irrigation.
Water is also supplied to the Timaru District Council for commercial and domestic purposes.
During the irrigation season, irrigators determine what their water needs are and order it on a daily basis.
These water orders are aggregated, and sufficient water is released from the dam to supply the irrigation requirements while ensuring minimum flows in the river.
Opuha Water has its own management and administration structure and personnel. The company contracts out the maintenance operation of the Power Station and river control gate to Manawa Energy. Manawa Energy has its operation centre in Tauranga and provides maintenance support from its base at Lake Coleridge.
Power Station Generation
The Opuha Dam facility includes a single turbine, 7MW hydro station at the base of the dam that generates electricity from all the water released from the lake storage. The power station provides a valuable contribution to the local electricity network with revenue from electricity sales accounting for approximately half of the Opuha Water’s income.
The power station operates every day, but of its hours of running depend on the amount of water required for the river downstream. Water from the power station discharges into a large ‘regulating pond’ where a control structure, the downstream weir, regulates the amount of water released into the Opuha River. This arrangement means the power station can operate intermittently at full load to get the best electricity price, while the flow into the river is managed at a consistent, natural level.
The power station is monitored operated under contract by Manawa Energy from its Control Centre in Tauranga. and the Maintenance support is based at Lake Coleridge, approximately 60km northwest of Methven and 170km from Lake Opuha.
The electricity connection is into Alpine Energy’s network and on to Transpower’s national grid via substations at Fairlie and Albury. The amount of electricity generated annually is entirely dependent on the hydrology of the catchment (lake storage and downstream water demand). Output can vary considerably from year to year and for any particular month.
Some Facts and Figures:
Hydro Turbine: 7MW Horizontal Francis Turbine (made by Kvaerner of Sweden)
Operating Parameters: Maximum Head 50m (range 28m to 50m); 16 cumecs at full load
Generator: Horizontal Generator operating at 475rpm, 6.6kV
Output: 11kV connection to Fairlie Substation (Alpine Energy)
Grid Connection: Albury Substation (Transpower)
Average Annual Generation: 25 GWh (range 15GWh to 37GWh)
Producing enough electricity to generate approximately 5,000 Kiwi Homes annually (2022)
Image Below: Looking down into the Opuha Power Station
