HIGH ELEVATION MEADOWS AS GROUNDWATER RESERVOIRS: QUANTIFYING VOLUMETRIC STORAGE

High elevation meadows trap and store snowmelt from the larger watershed, which is then later released through baseflow to streams and root water uptake. Previous storage models of high elevation meadows assumed a uniform thickness of meadow sediment. Although these previous models were able to close the water mass balance, it is unclear if these assumptions will hold under future climate scenarios that lead to earlier or less snowmelt resulting in drier and longer growing seasons. In order to test these assumptions, improved spatial resolution of bedrock depths are needed to qualitatively and quantitatively identify geometric controls of volume of groundwater storage. A ground-penetrating radar (GPR) survey was conducted in Tuolumne Meadows, CA in order to identify bedrock depths. Bedrock depths in Tuolumne Meadows were found to be relatively shallow (<5 m) in the central and eastern sides of the meadow, with more variable depths (0-24+ m) in the western side. A suite of numerical models tested the true bedrock geometry processed from the GPR survey against uniform depth models on spatial and temporal scales for a range of aquifer properties. In each model scenario, volumetric storage was quantified throughout the growing season with attention to the scenario’s ability to support baseflow and ecologic function. Preliminary results suggest that volumes of groundwater in high elevation meadows are most sensitive to bedrock geometry, but are also affected by stream inflow rates and heterogeneity.