Response of the Rotorua geothermal system to exploitation and varying management regimes

Exploitation of the Rotorua geothermal system started in the 1920s, but during 1967± 1986 the number of wells and mass withdrawal greatly increased. Natural surface activity waned in the 1970s, prompting public concern, which led to a monitoring programme (1982), enforced closures of many wells (1987), and punitive royalty charges (1987). During the well closure programme, mass withdrawal was reduced by about 60%. Within one year, water levels increased by 2 m and pressures by 0.02 MPa. Since then, levels and pressures have continued to rise gradually. Many surface thermal features have shown recovery: geysers have resumed stronger or longer duration eruptions, springs have recommenced or strengthened over¯ows, and the frequency of hydrothermal eruptions has decreased. Some failed geysers have not yet recovered, indicating recovery is slow or that the bore closure programme may not guarantee recovery of all surface features. 7 2000 CNR. Published by Elsevier Science Ltd. All rights reserved