Interpretation of Repeat Shallow Temperature Surveys at Wairakei and Broadlands Fields

Abstract

Repeat 1 m depth temperature surveys indicate significant cooling in the Wairakei production borefield, and little change at Broadlands field since the late 1960's. In the area of decreased temperature at Wairakei, the groundwater level has fallen by m, but the temperature at the water level has increased during this time. These changes appear to be due to the movement of water vapour in a 10-20 m thick zone above a boiling or near-boiling water surface. descends below about 20 m depth, the shallow thermal anomalies small and may be by other perturbing factors such infiltrating rainwater In areas with a falling groundwater surface, thermal anomalies may only persist if the groundwater is strongly boiling, and the steam flow is sufficient to reach the surface before significant condensation.