Simple Models for Changes in Spring Flows at Wairakei

Abstract

A model which considers mixing, Darcy flow, and geothermal reservoir pressure is applied to analyse the changes in flow rate and chemistry of spring SP18 during development of Wairakei geothermal field. The model suggests that, prior to development, the observed flow rate of 3 Vs was comprised of about 2.1 Vs from the deep reservoir and about 0.9 Vs from groundwater. As the pressure in the reservoir declined, the reservoir components declined but the groundwater component remained near constant until the spring had nearly ceased flowing. The source of the spring is estimated at -1 15 mRL, assuming the spring was fed by a single source. Values of KA for the spring feeder are between 2800 and 1 1400 m3/day.