Natural features at Ohaaki Geothermal System have been irreparably damaged by development for power generation.
Historically, there were alkaline hot springs and bathing pools at Ohaaki. Some of these springs and a sacred cave were flooded when the river level was raised to fill Lake Ohakuri for the hydro-electric power scheme in 1961.
The Ohaaki Ngawha (boiling pool) is the dominant remaining natural feature of the field. Before the area was developed, the large Ohaaki Ngawha with its clear, pale, turquoise-blue water and extensive white sinter terrace was described as "the most handsome pool in the whole thermal area"1.
When development commenced, the extraction of geothermal fluid made the water level in the Ohaaki Ngawha drop. This caused the partial collapse of the delicate sinter edge and the white silica formations weathered to a dull dirty grey. The sinter terrace is now cracking and has plants growing through it.
The Ngawha is now fed by geothermal bore water, which contains chemicals added to prevent silica depositing in the bore pipes.
Most of the other flowing surface features at Ohaaki have dried up because of the extraction of geothermal fluid. Before development Ohaaki had:
- several mud pools heated by steam
- hot pools isolated from ground water by a layer of mineralised earth, also heated by steam
- hot springs producing chloride water and depositing sinter.
Very few of these features now remain as anything other than dry hot ground. Most of the springs and pools have dried up and the mud pools have cooled.
The area of steaming ground has expanded, and now an urupa has steam rising through the graves, and the ground has opened up in places.
The only features still containing hot water are those near the Taupo Lucerne Plant, which has a resource consent to discharge geothermal water to large shallow natural geothermal pools.
Subsidence caused by geothermal development has caused a road to become covered by the Waikato River, and the Ohaaki marae is similarly threatened.
When the power station opened in 1988, it produced 108 megawatts of electricity. Because of cooling of the resource as a result of development, it now produces only 45 megawatts.