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A preliminary study of the regional groundwater flow in the Meager Mountain geothermal area, British Columbia

University of British Columbia

The Meager Mountain geothermal area is situated 160 km north-northwest of Vancouver, British Columbia. Various types of existing and field-generated geological and hydro-geological data were employed to fully evaluate the groundwater flow regime of the study site. Mathematical modelling was carried out to determine the feasible range of regional groundwater flow characteristic in the area. Meager Mountain is a volcano comprised mainly of ande-site and dacite flows, breccias and ash. It became active in the Pliocene, fracturing the Tertiary and older granitic basement rocks through which it erupted. Subsequent alpine glaciation has deposited unconsolidated deposits of variable thickness in the valley bottom. It can be shown that the most likely position for the water table is at an intermediate elevation in the mountain system. Apart from a very few springs at higher elevations, the discharge area is believed to be confined to the portion of the valley covered by unconsolidated deposits. Meager Creek Hotsprings and Pebble Creek Hotsprings are both located in this suggested discharge area near stream level. Water balance calculations for the Lillooet River basin and baseflow determinations in the Meager Creek basin indicate that 14.5 to 17% of the total precipitation enters the groundwater system. Mathematical modelling indicate that the amount of groundwater discharge is dependent on the hydraulic conductivity distribution and water table configuration but independent of the depth of the flow region. The percentage of total precipitation entering the groundwater zone is calculated to be 14-18%, correlating well with the water balance and baseflow calculations. The simulations were used to estimate the hydraulic conductivity of the various materials in the Meager Mountain system. The representative hydraulic conductivities were found to be 10⁻² to 10⁻⁵ m/s for the unconsolidated deposits, 10⁻⁷ to 10⁻⁸ m/s for the basement rock and 10⁻⁴‧⁵ to 10⁻⁸ m/s for the volcanics. The vertical hydraulic conductivity may be as much as 5 times greater than the horizontal in the basement rocks. The horizontal hydraulic conductivity may be as much as 5 times greater than the vertical in the volcanics rocks. Similar vertical hydraulic conductivity values probably exist in the volcanics and in the basement. Recommendations for future work at the Meager Mountain geothermal area include the initiation of a detailed water balance in the south reservoir area, a fracture survey of the volcanic rocks, continued mathematical modelling, and hydraulic conductivity measurements in deep drill holes.

Text

2010-03-25

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http://hdl.handle.net/2429/22494

Geological Sciences

University of British Columbia

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