7.2.1 Background and Explanation
The Waikato Region contains most of New Zealand’s geothermal areas. The Regional Geothermal Resource can be divided naturally into management units known as geothermal systems and this Plan is based on this distinction. A geothermal system is an individual body of geothermal energy (including geothermal water) not believed to be hydrologically connected to any other in the upper few kilometres of the Earth’s crust. There may be more than one heat upflow contributing to a geothermal system. A geothermal system may be indicated by geothermal surface features such as an isolated hot spring or set of hot springs, or a much larger set of features. Alternatively, there may be no visible expression at the surface.
The main geothermal systems in the Waikato Region are identified in Figure 7.1
Further background information on the geothermal resource within the Waikato Region, including the uses and values associated with the resource, can be found in the Waikato RPS and other documents produced by Waikato Regional Council (Waikato Regional Council). This Plan should be read in conjunction with the RPS.
The legend of Ngatoroirangi describes how geothermal energy arrived in New Zealand and gives a basis for understanding the relationship tangata whenua in geothermal areas have with the resource. The concept of kaitiakitanga requires tangata whenua to respect the environment and to ensure resources are available for future generations. Kaitiakitanga is an important concept in decision making that involves the notion of guardianship as well as tapu, mana, mauri and ahi kaa. It places an obligation on tangata whenua as Kaitiaki to ensure that geothermal resources are maintained and handed to future generations in a healthy condition. Tangata whenua with particular interest in geothermal energy are people from Waikato-Tainui, Te Arawa, Ngati Tuwharetoa, Ngati Tahu, Ngati Raukawa, Maniapoto and Hauraki.
Therefore, in the management of the Regional Geothermal Resource, there is a need to recognise the importance of protecting the variety, and as much as is practicable, extent of the characteristics and values that are associated with the resource, as well as recognising its development potential. The management framework put forward in this Plan seeks to meet these two directions while avoiding degradation of the Regional Geothermal Resource.
This is achieved by identifying the geothermal systems in the Region for different management regimes. There is a clear distinction between the Region’s large and small geothermal systems. The large systems are all found in the Taupo Volcanic Zone, the triangular-shaped active volcanic zone stretching from an apex at Mt Ruapehu out to White Island (Whakaari) and beyond. These systems each cover and area of several square kilometres at least, and contain large volumes of heated rock and geothermal fluid with temperatures of up to 350 °C. The small geothermal systems are scattered throughout the region, including the Taupo Volcanic Zone. They generally produce water of less than 100 °C, and are small in area and volume of water discharged.
Each of the 15 known large geothermal systems within the Region is substantially different from the others in terms of its extent and volume, local geology, reservoir dynamics, and surface outflows.
Horohoro is a waning system, with few existing surface outflows but large areas of ancient sinter, indicating that it has been substantially more active than it is today.
Mangakino is the western-most large system in the Taupo Volcanic Zone. It also has few surface features, most of which are now under Lake Maraetai. However, it does not appear to be waning in the same way as Horohoro.
Mokai has its main upflow near the Mokai settlement, with a subsurface outflow flowing eleven kilometres north to the Waikato River. It has few surface features and few natural and physical resources that would be substantially adversely affected by subsidence, should it occur as a result of system development. Mokai supports a power station and a glass-house complex providing employment for many local people.
Ngatamariki was postulated to have a hydrological connection to Orakeikorako; however resistivity measurement and other data have effectively ruled that out. It has unusual travertine sinters, but none of the springs vigorously deposit sinter.
Ohaaki was developed in the 1970s, but cold water drawdown near production wells has cooled the production aquifer and electricity output is decreasing. Before production commenced there were several geysers and sinter-depositing springs, including the spectacular Ohaaki Ngawha, which is considered a taonga by Ngati Tahu. The flow to these springs was destroyed by development, and now the Ngawha is kept full by the input of bore water. Production has also increased the surface expression of steam, and an urupa has become the site of new fumaroles. The site of the main Ngati Tahu marae, situated by the Waikato River, is expected to be inundated as a result of subsidence. As well as a geothermal power station, there is a geothermally-heated timber-drying plant at Ohaaki.
Rotokawa supports a power station that has plans for expansion. An extensive area of altered ground has been the site of a sulphur-mining operation, and substantial sulphur deposits remain. It has a few sinter-depositing springs, and a large area of geothermal vegetation. The geothermally-influenced Lake Rotokawa provides habitat for a unique species of leech, that is adapted to live in the highly acidic water, which has a pH of 2.
Wairakei-Tauhara once supported two large geyser fields, but the flow to these was destroyed by the geothermal development for the Wairakei Power Station and by works in the bed of the Waikato River associated with the installation of the Taupo Control Gates for hydroelectric developments. The Wairakei Power Station has been operating for nearly 50 years, and was the second geothermal power station ever built in the world. Part of the Wairakei field has experienced subsidence of up to 15 metres as a result of the geothermal development. Taupo urban area is built over part of the Tauhara geothermal field, and there are many geothermally-heated homes, motels, and swimming pool complexes.
Atiamuri has two large sinter pools in a Department of Conservation reserve. There are several other sinter-depositing springs in nearby farmland, and some that were submerged by the creation of Lake Ohakuri.
Tokaanu-Waihi-Hipaua has several geysers and sinter-depositing springs at Tokaanu, most of which are in a Department of Conservation reserve. Waihi village also has hot springs at the edge of Lake Taupo, and directly above Waihi there is a large expanse of steaming ground on a steep hillside at Hipaua. This has been the site of several fatal landslides, as chemicals in the geothermal steam destroy the structure of the soil, causing it to slip away and fall onto the village. There are many small uses of geothermal fluid at Tokaanu, including homes, public baths, and accommodation establishments.
Reporoa shares a boundary with the Waikite-Waiotapu-Waimangu system, and may be hydrologically linked to it. Many of the sinter-depositing springs at Reporoa are adversely affected by drainage of the surrounding land for farming purposes.
Te Kopia shares a boundary with the Orakeikorako system, and may be hydrologically linked. It has a relatively pristine area of geothermal vegetation extending from the base of the Paeroa Scarp to its top, all within a Department of Conservation Reserve and surrounded by mature forest. It has a rare mud geyser and many other pools at the base of the scarp, and several super-heated fumaroles pumping out large volumes of steam at the top of the scarp.
Orakeikorako has New Zealand’s largest concentration of geysers and sinter-depositing springs, and supports a tourism operation. There are now approximately 35 geysers within the tourist area, but before the creation of Lake Ohakuri drowned a large part of the geyser field, there were approximately 120 geysers.
Horomatangi lies under Lake Taupo which is the caldera of an active volcano. Investigation with a submarine has revealed sinter spires and fumaroles on the bed of the lake.
Tongariro on Mt Tongariro is New Zealand’s only high-altitude geothermal system. There are outflows at Ketetahi, Te Maari, and the Tongariro summit. Ketetahi Springs is a taonga of Tuwharetoa and is on private property with access denied, surrounded by the Tongariro National Park. Within Ketetahi Springs there are unusual acid geysers, and the geothermal area supports a high-altitude thermophilic midge that is not know to live anywhere else. Tongariro geothermal system extends into the Manawatu-Wanganui Region.
Waikite-Waiotapu-Waimangu system has many geysers, sinter-depositing springs, mud pools and other features, including the spectacular Champagne Pool at Waiotapu. There is a large tourist operation on the Waiotapu field, and one of the world’s largest bee-keeping operations uses geothermal heat for warming hives and processing honey. Most of the Waimangu field is in the Bay of Plenty Region. Waimangu is the youngest geothermal field in the world, having been created in the 1886 eruption of Mt Tarawera. It also has a large tourism operation.
In accordance with the policies and methods in the Regional Policy Statement, large geothermal systems are identified as Development, Limited Development, Research, or Protected Geothermal Systems. The Research category includes undiscovered large systems.
All other geothermal systems are treated as Small Geothermal Systems. The policy reflects the primary uses or values associated with those Small Geothermal Systems, while ensuring that the variety, and as much as is practicable, extent, of the regional geothermal resource is maintained.
Key aspects of managing the Regional Geothermal Resource are ensuring that use of the resource is efficient and that the potential of natural and physical resources to meet the reasonably foreseeable needs of future generations is not compromised. This is addressed by:
- Identifying some Protected Geothermal Systems, where the natural characteristics of the system will be protected;
- Requiring a System Management Plan for each Development Geothermal System which will promote the efficient management of takes uses and discharges in accordance with the objectives and policies in the Regional Policy Statement and this Plan;
- Ensuring that, in all other systems, use of the geothermal resource conserves geothermal energy and water as much as practicable;
- Recognising that future generations may have more and better choices than present generations as to how to meet their energy requirements, and therefore allowing controlled depletion in some geothermal systems while not compromising the ability of future generations to meet their reasonably foreseeable needs.
Another important aspect of the management of the Regional Geothermal Resource is avoiding, remedying, or mitigating adverse environmental effects. This includes not only the actual and potential effects associated with the use of the Regional Geothermal Resource, but also the effects of other activities on the Regional Geothermal Resource.
The following sections of this Module are intended to expand upon the issues, objectives, and policies of the Regional Policy Statement and provide clear direction in terms of regional council functions for addressing those resource management issues. This has been achieved by providing more detail in relation to the nature of the resource management issues associated with geothermal resources and providing specific objectives, policies, and methods that are intended to address those issues.
Figure 7-1: Map of the Geothermal Resources of the Waikato Region