Zygadlo, M.; Rae, A.J.; Reeves, R.R.; Wallin, E.; Pohatu, P. 2015 Te Puia Springs, East Coast, New Zealand, low enthalpy geothermal review. Lower Hutt, N.Z.: GNS Science. GNS Science report 2015/04 36 p.
Abstract: This report summarises the character and historical use of the Te Puia Springs area from both a cultural and scientific perspective. It describes some of the traditional (indigenous) and historical uses of geothermal resources at Te Puia Springs and examines scientific findings and current collaborative work, in order that the resource may be better understood and managed in the future. The East Coast of New Zealand is an active accretionary prism of uplifted marine sediments, with Te Puia located near the south-eastern extent of the East Coast Allochthon. The community, or hapu, predominantly resident in the geothermal area of Te Puia Springs is known as Te Whanau a Iritekura. Historically, the thermal pools and springs have been used by Mâori for healing, medicinal and domestic uses. Commercial development of the thermal springs occurred in the early 20th century, with recent use of the thermal water in the Te Puia Springs Hotel and Te Puia Hospital. Geochemical data from previous work show that sodium and chloride are the dominant components of the geothermal surface waters, with a chloride/bromide ratio that suggests a seawater influence. The water temperature of the springs ranges from 54 – 69°C. Although previous geochemical work suggests shallow reservoir fluid temperatures of about 100°C, fluid temperatures of between 200 – 330°C could occur at depths (6 – 11 km) where normal conductive temperature gradients of about 30°C/km . Magnetotelluric (MT) and audio-magnetotelluric (AMT) studies were performed to determine the resistivity structure in the Te Puia area. Two-dimensional modelling of the data shows limited resistivity contrast in the shallowest two kilometres, but close correlation with surface evidence of faulting and calcite sinter (travertine) deposits. A region of high resistivity at 3 km depth likely corresponds to the interface between the East Coast Allochthon and the basement greywacke. There is no reliable evidence in the two-dimensional resistivity model of a large reservoir of hot water, or clear permeable pathways for the geothermal water to move from source to the surface. The potential exists at Te Puia for further direct utilisation of the thermal springs, in addition to usage by the local hospital (Te Whare Hauora O Ngâti Porou). The total flow rates from springs across the thermal area have been estimated to be 8.7 l/s, with a minimal thermal potential of 1.8 MW. These values are low for electricity power production, but do not preclude finding an appropriate application of the resource that suits the needs of local- and/or district-wide communities. Low-enthalpy geothermal resources can be used for a wide range of domestic, agricultural and industrial applications that involve direct use of the heat. Various low-enthalpy applications for resources with temperatures <100°C are summarised (including industrial drying and washing, aquacultural and horticultural, refrigeration and space heating applications) a nd several case studies of low-enthalpy direct-use applications in New Zealand and internationally, are summarised. (auth)
