| Title | Groundwater Recharge to Geothermal Systems in the Taupo Volcanic Zone Assessed with Water Budgets and Three-Dimensional Geological Models |
|---|---|
| Authors | P.A. White, C. Tschritter, and R. D. Henderson |
| Year | 2012 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Water budgets, groundwater recharge, stream baseflow, Tauranga, Upper Waikato River, geothermal system recharge. |
| Abstract | Surface and groundwater budgets in the Taupo Volcanic Zone (TVZ) are developed at the sub-regional scale using hydrological observations and three-dimensional geological models to assess groundwater recharge to geothermal systems. Observations of rainfall, evapotranspiration, rainfall recharge to groundwater and surface flows (baseflow and runoff) show key features of surface and groundwater flows associated with volcanogenic units. Firstly, rainfall recharge to groundwater is typically a large percentage of rainfall. Rainfall recharge measurements with lysimeters at Kaharoa north of Rotorua show that rainfall recharge is approximately 50% of rainfall which is consistent with a surface water and groundwater budget study of the western Mamaku Plateau. Secondly, most rainfall recharge to groundwater discharges at the ground surface as baseflow in streams. Surface flows are dominated by baseflow and runoff is a small proportion of surface flow as demonstrated by field measurements and analysis of surface water hydrographs. For example, surface baseflow is typically 94% of total surface water flows in the Waikato River catchment between Karapiro Dam and Lake Taupo as demonstrated by an analysis of surface water hydrographs. Groundwater recharge to deep TVZ systems (including geothermal fields) is a small proportion of total rainfall recharge to groundwater. Groundwater recharge rates to the deep TVZ systems are possibly an important control on the location of geothermal activity as demonstrated in Ohakuri hydropower dam sub-catchments. In this area, many geothermal systems (e.g., Waiotapu, Te Kopia and Reporoa) are located in northern and western sub-catchments where deep groundwater recharge is relatively high. In contrast, few geothermal systems are located in eastern sub-catchments where water budget equations estimate no deep groundwater recharge from the ground surface. |