The Opuha scheme operates by releasing water into the Opuha River which flows into the Opihi River. Irrigation takes are from both the Opuha and Opihi rivers.
Irrigation water is supplied to a number of sub-schemes (Levels Plain, Kakahu, Totara Valley, Sutherlands) off these rivers which distributes the water through distribution races and channels. The water is pumped from these races and channels by the land owners. Other irrigators pump from the river either through galleries or adjacent bores. There is less than 2% of the irrigated area remaining in borderdyke irrigation.
Water is also supplied to the Timaru District Council for commercial and domestic purposes.
Irrigators determine their irrigation requirements and order their water on a daily basis.
These water orders are aggregated and sufficient water is released from the dam to supply the irrigation requirements as well as ensuring the minimum flow is maintained 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 TrustPower. TrustPower have their Operation Centre in Tauranga and maintenance support from their base at Lake Coleridge.
Power Station Generation
The Opuha Dam facility includes a 7MW hydro station at the base of the dam that generates electricity with all the water that is released from the lake storage. The power station provides a valuable contribution to the local electricity network and the revenue from the electricity sales accounts for approximately half of the company’s income.
The power station operates every day but the amount of running is dependent on the amount of water that is required for the river downstream. The water from the power station discharges into a large ‘regulating pond’ and then a control structure at the bottom end of the regulating pond (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 operated and maintained under contract by Trustpower. The station is monitored and operated from their Control Centre in Tauranga and the maintenance support is based at Lake Coleridge approximately 60km north west of Methven and 170km from Lake Opuha.
The electricity generated from the power station is sold under a Power Purchase Agreement currently with Pulse Energy.
The electricity connection is into Alpine Energy’s network and onto Transpower’s national grid via the 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). The output can vary considerably from year to year and for any particular month. The graph below gives an indication of the historical variability.
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)
Average Revenue (2007-2014): $1.7m (range $1.0m to $2.3m)