| Abstract/Description or Keywords |
Groundwater-surface water interactions control the extent and character of floodplain hyporheic zones, and play an important role in the function of riparian ecosystems. This study used geologic, hydrogeologic, hydrochemical, and numerical simulations to characterize hyporheic zone and groundwater-surface water interactions within highly permeable floodplain deposits of the North Vancouver Outdoor School (NVOS), Cheakamus Valley, where groundwater-fed salmonid spawning habitat has recently been rehabilitated. NVOS floodplain groundwaters and spawning channels are recharged by a combination of Cheakamus River water and upwelling deeper groundwaters. Flowpath analysis and water level versus stage correlation reveal the Cheakamus River to be the dominant source for floodplain groundwaters and spawning channels. Vertical groundwater flow is insensitive to Cheakamus River stage, indicating that upwelling deeper groundwaters may be present. Floodplain field chemistry monitoring indicates that cation exchange, complexation, and mixing of recharging river water and deep upwelling groundwaters are the likely dominant chemical processes operating within shallow NVOS sediments. Two regional hydrogeologic conceptual models are presented for the lower Cheakamus Valley. Regional model A proposes that all groundwaters upwell into a shallow aquifer located above the Cheekye Fan. Regional model B proposes that deep groundwater diverges and flows in separate aquifers located above and below the Cheekye Fan. Regional groundwater flow regimes were numerically simulated using Visual MODLFOW. Both numerical models reproduce conceptual and observed groundwater flow regimes, but further regional-scale sampling is required to determine which model is more appropriate. |
