Impact of complex aquifer geometry on groundwater storage in high-elevation meadows of the Sierra Nevada Mountains, CA

Recent research has indicated that Sierra Nevada meadows are hydrologically more complex than previously considered. Improved understanding of the effects of aquifer parameters and climate change on water resources in and downstream of meadows is critically needed to effectively manage mountain meadows for ecosystem services and watershed contributions. This research investigates the roles of bedrock geometry, saturated hydraulic conductivity, and meadow gradient in affecting groundwater storage dynamics and surface-water outflows in site-scale high-elevation meadows. Under current and projected lower snowpack conditions, we modeled groundwater flow in representative high-elevation meadows considering 2 conceptual aquifer thickness models: uniform and variable thickness. Spatially, variable aquifer thicknesses interpreted from bedrock depths (0–28 m) were identified from a high-resolution ground-penetrating radar survey conducted at Tuolumne Meadows, CA. Our interpreted bedrock surface indicated several buried U-shaped valleys including a buried ridge that separates 2 U-shaped valleys. Groundwater flow simulations show that an increase in meadow gradient and hydraulic conductivity led to a decrease in seasonal storage and an increase in surface-water outflow. However, models with varying bedrock geometries change the magnitude and timing of these processes. Uniform thickness models overestimated storage at the model edges and resulted in higher projected volumes of water being released to streams earlier than previously observed.