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University of British Columbia (2015)

Physical measurements of groundwater contributions to a large lake.

Pyett, Nicole Jean

Titre : Physical measurements of groundwater contributions to a large lake.

Auteur : Pyett, Nicole Jean

Université de soutenance : University of British Columbia

Grade : Master of Science (MS) Environmental Sciences, 2015

Population increases and climate change are expected to increase water stress in the semi-arid Okanagan Valley in the Interior of British Columbia. Groundwater discharge from the largest unconsolidated aquifer system in the Okanagan Valley to Okanagan Lake was directly measured between September 2011 and August 2013. Seepage meter measurements (331) and gradient calculations (73) were used to measure flow from the Kelowna aquifers in an effort to constrain groundwater values in a basin-scale water-balance model constructed to inform water use and planning decisions within the Okanagan Valley. The complexity of the subsurface environment in the Kelowna area led to the construction of a 2-D MODFLOW transect to provide a sensitivity analysis of the percentage of total flow captured within the study area using a reasonable range of hydraulic conductivity values for the known confining and confined layers. Forty-two MODFLOW scenarios estimated 26% - 100% of the total flow from the Kelowna aquifers to Okanagan Lake was captured within the study area. Long-term station seepage meter measurements showed a large range of annual variabil^ity with flux measurements which ranged from 10-¹¹ to 10-⁹/10-⁸ m³/m²/s. A substantial reduction in flows observed within the study area between study year one (4.1 x 10⁵ m³) and study year two (2.9 x 10⁵ m³) was potentially due to anthropogenic water extractions. The annual groundwater discharge estimate of 3.7 x 10⁵ m³ found flow from the Kelowna aquifers to be less than one percent of some previous estimates and likely less than seven percent of the volume being extracted from upgradient aquifers. Long-term provincial potentiometric monitoring indicated groundwater pumping rates have likely exceeded recharge in some Kelowna aquifers for the past 34 years. Other studies using modelling and geochemistry have suggested groundwater pumping is inducing recharge from adjacent fluvial water bodies in some areas. The low discharge from the Kelowna aquifers to Okanagan Lake suggests cautious groundwater extraction rates need to be established in the Kelowna area to ensure the groundwater system can continue to support both human and environmental water needs.

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Page publiée le 23 novembre 2016, mise à jour le 5 février 2018