Groundwater Storage Dynamics in High Elevation Meadows Affected By Complex Aquifer Geometry

Abstract:

The Sierra Nevada represents a cascading hydrologic cycle where snowpack, meadow aquifers, and streams are all hydrologically connected. Monitoring the water balance within high elevation meadows is vital in order to effectively quantify watershed scale storage dynamics, which support meadow ecological communities as well as downstream users. In this case, much of the San Francisco, CA water supply originates from the seasonally released snowmelt from high elevation meadows to downstream reservoirs. In previous studies of high elevation meadows, the water mass balance was closed under the assumption that the meadow sediment was spatially uniform in thickness. Here, complex aquifer geometry was identified in Tuolumne Meadows, CA from a high-resolution ground-penetrating radar survey. This new geometry was compared to the previous geologic model of high elevation meadow aquifers using numerical models simulating both current and future snowmelt scenarios. In addition, the impact of variability in meadow sediment and slope were evaluated to quantify storage properties of representative Sierra Nevada meadow types. Results demonstrate that the previous aquifer geometry model significantly overestimates both the spatial and temporal volumetric storage and release of groundwater to streams. These implications are noteworthy for ecosystem restoration and water supply strategies that aim to rectify water supply to and from these meadows especially when considering drought scenarios. In order to move forward and effectively and efficiently monitor the seasonal volume of water stored within the Sierra Nevada, complex aquifer geometry within high elevation meadows must be considered.