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

Exploitation of the Rotorua geothermal system started in the 1920s, but dur ing 1967-1986 the number of wells and mass withdrawal greatly increased. Na tural 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 inc reased by 2 m and pressures by 0.02 MPa. Since then, levels and pressures h ave continued to rise gradually. Many surface thermal features have shown r ecovery: geysers have resumed stronger or longer duration eruptions, spring s have recommenced or strengthened overflows, and the frequency of hydrothe rmal eruptions has decreased. Some failed geysers have not yet recovered, i ndicating recovery is slow or that the bore closure programme may not guara ntee recovery of all surface features. (C) 2000 CNR. Published by Elsevier Science Ltd. All rights reserved.