Tauhara Geothermal System
Location and general description
The Tauhara Geothermal Field is located within the Waikato Region, east of Taupo township and is part of the Wairakei-Tauhara Geothermal System. It interacts with the Wairakei Field, located 8 km north of Taupo; the boundary between the fields is placed at the Waikato River. The field covers an area of about 18 to 35 km2.
The Waikato Regional Plan classifies the Wairakei-Tauhara Geothermal System as a Development Geothermal System where the take, use and discharge of geothermal energy and water will be allowed, while:
- remedying or mitigating significant adverse effects on Significant Geothermal Features; and
- avoiding, remedying or mitigating adverse effects on other natural and physical resources including overlying structures (the built environment).
This classification is based on:
- The system is already subject to large scale energy use and development
- Existing surface features significantly impaired by legally established large takes.
- No evidence of a flow of subsurface geothermal fluid to or from a Protected Geothermal System.
Local Geology and geophysics, wells drilled, etc.
Tauhara has a shallow steam-heated aquifer that underlies part of the Taupo township and land further to the east and north. It has been extensively exploited, with over 400 shallow wells extracting heat or steam or water for domestic, commercial and other uses
The formations are:
- Greywacke basement – these ancient marine meta-sediments have been intersected in well TH17 at a depth of 2 km and will be found at increasing depths towards the NW of the field due to the rifting environment. Fluid flow will be through fractures.
- Tahorakuri Formation, Wairakei Ignimbrite and Waiora Formation – these are a series of ignimbrites and rhyolites, interspersed with other rhyolite and andesite units. In particular the Waiora Formation hosts a major geothermal production aquifer in the Wairakei-Tauhara Geothermal System.
- Huka Falls Formation – this consists of Upper, Middle and Lower units which in combination help to act as a leaky cap to the system and, while variable in thickness, extend to depths down to sea level.
- Oruanui Formation and Recent alluvium and tephra – these are relatively shallow strata that can host groundwater and some hot water tapped by shallow bores in the Taupo township.
The Crown drilled four deep (up to 1,200m) exploratory wells, TH1-4, in the 1960s and several monitor wells from the 1960s to 1980. Works Geothermal/Trustpower drilled TH5 to 500m in 1991. In 2002 Contact Energy initiated a drilling programme, with 25 wells drilled for field exploration, production and to carefully assess the subsidence potential. Deep wells drilled at Tauhara have found higher temperatures than Wairakei, adding to the evidence for multiple upflows. The maximum temperature recorded is 279°C. Production temperature is about 250 °C.
Significant Geothermal Feature types present include:
- Geothermally-influenced aquatic habitat (Onekeneke Stream)
- Geothermally-influenced water body (Onekeneke Stream)
- Geothermally-induced atmospheric microclimate
- Heated ground habitat
- Hydrothermal eruption craters
- Mud pools
- Recent sinter
Part of the Otumuheke area is of national significance because it is a good quality example of geothermal habitat, which includes nationally uncommon ecosystem types (geothermal stream margins, geothermally heated dry ground). The thermal swamp at the head of the Otumuheke Stream remains in excellent condition.
This site also contains sizeable populations of Christella aff. dentata (“thermal”) and Cyclosorus interruptus, and small populations of two other At Risk fern species: Hypolepis dicksonioides and Nephrolepis flexuosa.
Broadlands Road is of regional significance because it is protected under the Reserves Act (1977) as a Scenic Reserve, contains a large population of geothermal kānuka (an ‘At Risk’ species), and comprises a relatively large example of geothermal habitat, which includes nationally uncommon habitat types (geothermally heated dry ground, fumaroles).
Crown Rd site is of regional significance because it comprises a relatively large example of geothermal habitat, which includes nationally uncommon habitat types (geothermally heated dry ground, fumaroles). It provides habitat for geothermal kānuka, an ‘At Risk’ species. Areas of hydrothermally altered soils and heated soilfield are also present.
Waipahihi Valley is of regional significance because parts of the site are protected as a Conservation Area. It also provides habitat for four ‘At Risk’ species (geothermal kānuka, Hypolepis dicksonioides, Christella aff. dentata (“thermal”), and Cyclosorus interruptus).
Existing and historical geothermal uses
The Tauhara geothermal resource has been used for domestic purposes and bathing for centuries. As part of the Taupo township it has been used for bathing and tourism since the 19th century.
Other than the domestic use mentioned earlier, Tauhara has two separate major operations: production for power generation and production for industrial heat supply. Contact Energy commissioned a new 20 MW(th) process heat supply to Tauhara Tenon Kilns in 2006. Contact commissioned the 23 MW(e) Te Huka Power Station in 2010.
Contact Energy has been granted Resource Consents (a license) to generate up to an additional 250 MW(e) at Tauhara and the project is being progressed to a point that would enable the start of construction once market conditions are favourable. Development must take into account the potential adverse environmental effects on the surrounding Taupo urban area.
Inferred size of resource
Based on stored heat models, the energy development potential is about 220 MW(e). Recent numerical reservoir simulation have shown that greater than 250 MW(e) is sustainable.