SNOWMELT-INDUCED HYPORHEIC PUMPING IN TUOLUMNE MEADOWS, YOSEMITE NATIONAL PARK, CA

Diel fluctuations in streamflow and stream stage were observed in Tuolumne Meadows, Yosemite National Park, California. These stream stage fluctuations propagated into the riparian meadow aquifer and caused a daily pumping of the hyporheic zone. A model was developed using Fourier analysis to represent the stream stage fluctuations to simulate the resulting watertable fluctuations using a solution to the 1-D, linearized Boussinesq equation for groundwater flow. The work demonstrates that a substantial volume of water is pumped in and out of the aquifer via this process on a daily basis. The model and data show that snowmelt-induced groundwater fluctuations exhibit both reduced amplitudes and increased time lags at increasing distance away from the stream. This previously undocumented process of snowmelt-induced hyporheic pumping may have biogeochemical implications in the hyporheic zone including provision of important ecosystem services related to water filtration, thermal buffering, nutrient cycling, and water quality. Recognizing, quantifying, and monitoring snowmelt-induced pumping of the hyporheic zone and the ecosystem services it provides is critical for proper management and restoration of mountain streams.