Modern Heat Flow Estimates Of Whakarewarewa Geothermal Valley, Rotorua

Abstract

The Rotorua Geothermal Field (RGF) covers a surface area of approximately 18-28 km2 in the northwest region of the Taupo Volcanic Zone (TVZ). With an estimated natural heat-flow of 430 MW, the RGF is considered one of the larger geothermal systems within the TVZ. The RGF underwent a period of development and exploitation during the 1970s utilising fluids from the shallow ( less than 300m depth) aquifer. The mass withdrawal and consequent pressure reduction in the shallow part of the system resulted in diminished discharge and extinction of some natural surface features located around the Rotorua Township. A government-enforced bore-closure program was introduced in 1986 to manage and reduce effects of development on the shallow geothermal reservoir. Heat flow calculations from natural surface features are used to estimate the size of the geothermal reservoir and provide an insight into the health of the geothermal system. In 2010 a heat flow survey was undertaken by measuring temperatures and water flow of selected water features at Whakarewarewa, located on the southern boundary of the RGF. Lake Roto-a-Tamaheke is the largest geothermal feature in the Whakarewarewa area. This paper presents data and heat flow estimates for the Lake Roto-a-Tamaheke area and compares the heat flow measurements to previous estimates.