HYDROGEOLOGY OF VALLEY-FILL AQUIFERS IN THE NORTHERN OKANAGAN

Groundwater in the North Okanagan was investigated using an integrated physical, geochemical and numerical approach. The North Okanagan Groundwater Characterization and Assessment (NOGWCA) project began with an investigation of the geology and hydrostratigraphy of the North Okanagan region. The Deep Creek and Fortune Creek watersheds were found to contain multiple valley-fill aquifers.

The main valley is composed of several confined aquifers. The Spallumcheen A aquifer ranges from 30 to 90 m depth and is 45 to 90 m thick. This is the main aquifer utilized in the valley. It is recharged from via mountain system recharge (MSR) and via direct recharge in the valley bottom to unconfined aquifers at the valley edge. Detailed hydrometric data indicates groundwater recharge within the alluvial fan of Fortune Creek, and discharge to surface water in the lower reaches of Deep Creek. Valley side recharge at alluvial fans generates artesian conditions in the valley center. A second continuous confined aquifer is found at depths of 200 to 350 m. Additional discontinuous aquifers are found between 90 and 200 m, as well as at depths below 350 m in the parts of the main valley.

Groundwater and surface water geochemistry and isotopic character were used to determine the overall groundwater flow regime. Chloride mass balance was used to estimate recharge in the valley bottom and within the mountain bedrock system. Additional recharge information was derived from a integrated climate dataset and from data on agricultural irrigation and wastewater irrigation. Efforts to accurately quantify and understand MSR are hampered by sparse data on the geochemical character of bedrock aquifers. Analysis of the groundwater chemistry has assisted in detailing the aquifer interactions. Conservative elements and deuterium/oxygen isotopes were used in a mixing cell model (MCM) approach to assess groundwater flow between aquifers

FEFLOW was used for numerical simulations. The first stage modeled steady state conditions within the Spallumcheen A aquifer. Integrated surface water and groundwater modeling is to be carried out in the future. The groundwater flow modeling will contribute to subsequent water management decisions at the watershed scale. Climate change and economic change scenarios will be considered in the integrated surface water and groundwater modeling.