Waikaremoana Scheme description
The 138MW Waikaremoana Hydro Scheme comprises three hydro power stations – Kaitawa (36MW), Tuai (60MW) and Piripaua (42MW).
Kaitawa power station (36MW)
Lake Waikaremoana was created approximately 2200 years ago by a massive landslide which dammed the Waikaretaheke River. The natural outflow of the lake was originally leakage through the natural dam. In the 1950s, an attempt was made to seal some of the leaks and occasional surface flow over a natural crest to the Waikaretaheke River when the lake level was high enough in the bed of Lake Waikaremoana, to allow more water to pass through Kaitawa Power Station.
Kaitawa Power Station, commissioned in 1949, was the last power station to be constructed as part of the Waikaremoana Power Scheme and generates a maximum output of 36MW.
The station was constructed upstream of Tuai Power Station, alongside Lake Kaitawa, and is supplied with water directly from Lake Waikaremoana via tunnels driven through the natural dam. Previous to Kaitawa Power Station being developed, the stations at Tuai and Piripaua had only utilised water that naturally flowed out of Lake Waikaremoana by leakage or crest flow. The development of Kaitawa Power Station meant that water was taken directly from Lake Waikaremoana. Water from Kaitawa Power Station is discharged into a short canal and into Lake Kaitawa for use in two power stations downstream. Spillway structures also allow water to pass into the Waikaretaheke River.
Water can also be taken from Lake Waikaremoana via either the siphon system or spillway, both of which discharge water into the Waikaretaheke River. The siphon system is used either to bypass Kaitawa Station when it is not generating (the water can be used downstream in Tuai and Piripaua Power Stations), or when it is necessary to contain rising lake levels.
Tuai power station (60MW)
Lake Kaitawa was originally a small spring-fed lake and wetland. However, the construction of an earth dam and weir across the Waikaretaheke River in the mid-1930s allowed the water level to be raised by 3 metres, converting it into a permanent lake.
The lake today is the operational headpond for Tuai Power Station and is fed by water diverted from the Waikaretaheke River, which also has a number of springs that flow directly into it. Lake Kaitawa has an operating range of 2.6 metres.
The Tuai intake, through which water is taken to Tuai Power Station, is located on the eastern side of Lake Kaitawa. Tunnels and penstocks carry water to Tuai Power Station. Tuai Power Station has the highest head and generates the largest proportion of the Waikaremoana Power Scheme's total output. The station has a maximum output of 60 MW.
Piripaua power station (42MW)
Water is discharged from the Tuai Power Station turbines into Lake Whakamarino. This lake was created by construction of an earth dam across the Kahuitangaroa Stream. The earth dam contains a spillway structure and a sluice gate structure. The spillway structure incorporates an automatic tipping gate, which allows water to pass directly down the Kahuitangaroa Stream. Water is released here into the Kahuitangaroa Stream, which joins with the Waikaretaheke River a short distance downstream.
The Piripaua intake is located at the south-eastern side of Lake Whakamarino. Piripaua Power Station is located in the bed of the Waikaretaheke River. The residual Waikaretaheke River is diverted around the station and rejoins its original course approximately 200 m downstream. Water discharged from the station's turbines flows into the natural riverbed via a tailrace. Piripaua Power Station was commissioned in 1943.