Recovery of Rotorua geothermal field, New Zealand: Progress, issues and consequences

Recovery of most surface features in many parts of the Rotorua geothermal field (RGF) has continued as water levels rose and pressures increased following bore closures that began in 1986. However, the pattern of recovery of features is very variable, even within a relatively small area, with no apparent consistency as to location or type of feature. Most features in the Whakarewarewa Thermal Area that were affected by the pre-1986 pressure drawdown have recovered, but some have not. More puzzling is the behaviour of a few features (such as Waikorohihi and Mahanga geysers) that initially showed recovery, but later ceased activity. Chemical data indicate that for some features there has been an increase in the amounts of deep fluid reaching the surface, but in others there has been no change. Examination of seismic records suggests that the unusual behaviour is not related to local seismic activity. The recovery of many thermal features has been beneficial from a tourist and environmental viewpoint. However, there have been some detrimental occurrences. Following the decline and disappearance of thermal features before the bore closures, the vents of some features were inadvertently filled in and the land around them reclaimed and used for buildings or services. As water levels recovered after the closures, discharge to the surface recommenced, causing damage to buildings and associated services, resulting in several houses being damaged or forced to be relocated. In all cases, however, the discharges were from historically active vents. The data suggest that while most natural thermal features may recover from the effects of geothermal exploitation some may not, and in the case of Rotorua there does not appear to be any pattern or explanation for such non-recovery.