Abstract
Abstract. The utilization of geothermal reservoirs as alternative energy source is becoming increasingly important worldwide. Through close-range aerial photogrammetry realized by unmanned aircraft systems (UAS), this study investigates the surface expression of a leaking warm water reservoir in Waiwera, New Zealand, that has been known for many centuries but remained little explored. Due to overproduction during the 1960s and 1970s the reservoir has suffered significant pressure reduction, which resulted in the loss of artesian conditions and led to the desiccation of the hot springs in close succession. However, shortly after the recent shutdown of the primary user (Waiwera Thermal Resort & Spa) renewed artesian activity was reported by locals but no hot spring activity has been observed so far. Therefore, this study was carried out in October 2019 to assess the actual conditions of thermal activity in the area of the former hot springs. UAS with coupled thermal infrared cameras were used for thermal mapping and the obtained data show renewed activity of the hot springs on the beachfront of Waiwera. Faults and fractures were identified as important fluid pathways, as well as individual fluid conducting lithologies.
Highlights
Geothermal reservoirs are closely linked to the tectonic structure, porosity and permeability contrasts and may be altered by extrinsic processes, yet the details of surface manifestations are commonly difficult to monitor
By use of unmanned aircraft systems (UAS), the surface expression, morphology and temperature anomalies associated with geothermal activity can be monitored and accessed even in regions difficult to reach (James et al, 2020)
The Waiwera Thermal Groundwater Allocation and Management Plan, which was adopted by the Auckland Coucil in 1987 allowed the geothermal system to slowly recover but the production rates did not allow the return to artesian conditions or the reactivation of the hot springs (Kühn and Stöfen, 2005)
Summary
Geothermal reservoirs are closely linked to the tectonic structure, porosity and permeability contrasts and may be altered by extrinsic processes, yet the details of surface manifestations are commonly difficult to monitor. The Waiwera Thermal Groundwater Allocation and Management Plan, which was adopted by the Auckland Coucil (former Auckland Regional Water Board – ARWB) in 1987 allowed the geothermal system to slowly recover but the production rates did not allow the return to artesian conditions or the reactivation of the hot springs (Kühn and Stöfen, 2005). Shortly after the primary user (Waiwera Thermal Resort & Spa) shut down in 2018, locals have reported overflowing bores to the Auckland Council. This indicates a progressing recovery of the geothermal system including the return to artesian conditions. The knowledge of its rock properties (e.g., lithology, porosity and permeability), diagenetic alterations controlling porosity and permeability and affecting mechanical properties, structural inventory as the fracture network, the heat transfer, and all resulting interactions are crucial
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