Dawson, G.B. 1985 Ground temperature surveys at Parakai thermal area, Helensville (1956). [s.l.]: [s.n.]. Report / Geophysics Division 203 53 p.
Abstract: The Parakai geothermal area is about 3 km north of Helensville beside the Kaipara River. Prior to the development, in the late 1920's, of hot mineral baths fed from bores in the area, the only surface thermal manifestation was a solitary hot spring at what is now the Parakai Domain. In 1955 a contour map of the bore discharge temperatures was compiled by J. Healy. Because there were no bores to the east and north west of the Parakai Domain from which to obtain temperature data, a shallow temperature survey, measuring ground temperatures at depths of 4, 7, and 10 ft (1.22 m, 2.13 m and 3.05 m) was undertaken in 1956, to further determine the areal extent of the geothermal area. Bores in the area have depths varying from 23 m to 105 m. The highest bore discharge temperatures measured were about 65 deg C compared with the highest temperature of 32.9 deg C encountered at 10 ft (3.05 m) in the shallow temperature survey. The areal extent of the Parakai Thermal Area, shown by bore discharge temperatures greater than 40 deg C and 10 ft (3.05 m) temperatures greater than 20 deg C, was about 0.27 sq km. Bore discharges of greater than 30 deg C have been encountered over about twice this area. The ground temperature survey showed that, where there were data, there was fair agreement between a temperature contour map produced from bore discharge temperatures and temperature contour maps produced from temperatures measured at 4, 7 and 10 ft (1.22, 2.13 and 3.05 m) but less agreement with a contour map produced from temperature gradients between 7 and 10 ft (2.13 and 3.05 m). It was found that all wells discharging water in excess of 60 deg C lay within the 24 deg C isotherms at 4 ft (1.22 m), the 26 deg C isotherm at 7 ft (2.13 m) and the 28 deg C isotherm at 10 ft (3.05 m). Four cross sections have also been drawn to illustrate the relationship between the ground temperatures and bore discharge temperatures. Temperature measurements of water pumped from wells in the Helensville District outside the Parakai area showed temperatures of about 16 deg C. (auth)