Rotorua geothermal data : 1982-1990

By: Bradford, E. (DSIR Physical Sciences, Applied Mathematics Group. Wellington).
Contributor(s): DSIR Physical Sciences, Applied Mathematics Group. Wellington.
Material type: materialTypeLabelBookSeries: DSIR Physical Sciences report ; 2.Publisher: Wellington : DSIR Physical Sciences, Applied Mathematics Group, 1990Description: x, 143 p.ISSN: 1170-4438.Subject(s): HOT SPRINGS | ROTORUA | MONITORING | GEOTHERMAL RESOURCES | NEW ZEALAND | HYDROLOGY | TIME SERIES ANALYSIS
Incomplete contents:
I discuss the Monitor well data in three phases: monitoring - 1982-87; closure - 1986-88; management - 1988-present. During the monitoring phase a seasonal cycle imposed by summer to winter withdrawal changes dominated the Monitor well level changes. The Ministry of Energy Bore Closure Programme in 1987-88 caused an immediate rise in pressure in the Monitor wells and a slower recovery of thermal spring activity. After The Bore Closure Programme, much of the change in Monitor well level can be explained in terms of changes in rainfall pattern and temperature changes in the Monitor wells. I also discuss the factors other than geothermal pressure which influence the Monitor well levels. Changes in the Roto-a-Tamaheke are not so sharply defined as for the Monitor well data and I do not split this data. The water-flow, heat-flow and chloride-flow from Lake Roto-a-Tamaheke have increased slowly since the Bore Closure Programme. Combining some historical data with the pressure rise and withdrawal change during the Bore Closure Programme suggests that perhaps half of the pressure drop in the Rotorua geothermal field came from causes other than geothermal withdrawal. The most likely cause is the drop in mean rainfall from the 1960s to the 1980s. Some discussion of rainfall changes is given, together with some suggestions of other factors which influence spring behaviour. The final part of the report is on the mathematical techniques which had to be adapted and developed to analyse the Rotorua geothermal data. The main techniques were needed for the analysis of a large quantity of good timeseries data. (auth/CMB)
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Many refs; 47 figs; 6 tables

I discuss the Monitor well data in three phases: monitoring - 1982-87; closure - 1986-88; management - 1988-present. During the monitoring phase a seasonal cycle imposed by summer to winter withdrawal changes dominated the Monitor well level changes. The Ministry of Energy Bore Closure Programme in 1987-88 caused an immediate rise in pressure in the Monitor wells and a slower recovery of thermal spring activity. After The Bore Closure Programme, much of the change in Monitor well level can be explained in terms of changes in rainfall pattern and temperature changes in the Monitor wells. I also discuss the factors other than geothermal pressure which influence the Monitor well levels. Changes in the Roto-a-Tamaheke are not so sharply defined as for the Monitor well data and I do not split this data. The water-flow, heat-flow and chloride-flow from Lake Roto-a-Tamaheke have increased slowly since the Bore Closure Programme. Combining some historical data with the pressure rise and withdrawal change during the Bore Closure Programme suggests that perhaps half of the pressure drop in the Rotorua geothermal field came from causes other than geothermal withdrawal. The most likely cause is the drop in mean rainfall from the 1960s to the 1980s. Some discussion of rainfall changes is given, together with some suggestions of other factors which influence spring behaviour. The final part of the report is on the mathematical techniques which had to be adapted and developed to analyse the Rotorua geothermal data. The main techniques were needed for the analysis of a large quantity of good timeseries data. (auth/CMB)

AM

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