Direct Observation of the Depth of Active Groundwater Circulation in an Alpine Watershed
Abstract
AbstractThe depth of active groundwater circulation is a fundamental control on stream flows and chemistry in mountain watersheds, yet it remains challenging to characterize and is rarely well constrained. We collected hydraulic conductivity, hydraulic head, temperature, chemical, noble gas, and 3H/3He groundwater age data from discrete levels in two boreholes 46 and 81 m deep in an alpine watershed, in combination with chemical and age data from shallow groundwater discharge, to discern groundwater flow rates at different depths and directly observe active and inactive groundwater. Vertical head gradients are steep (average of 0.4) and thermal profiles are consistent with typical linear conductive continental geotherms. Groundwater deeper than ∼20 m is distinct from shallow groundwater and creek water in its chemistry, noble gas signature, and age (dominantly >65 years compared to <9 years). Together these results suggest low vertical groundwater flow velocities and a relatively shallow active circulation depth of ∼20 m. This hypothesis is tested with a simple 2‐D numerical fluid flow and heat transport model representing a hillslope transect through the two boreholes. The modeling indicates that the subhorizontally bedded sedimentary rocks underlying the basin are highly anisotropic with low vertical hydraulic conductivity, and at most ∼10% of bedrock recharge (equivalent to <2% of stream baseflow) flows below a depth of 20 m. The study demonstrates the considerable value of discrete‐depth hydrogeologic, chemical, and age data for determining active circulation depth, and illustrates an approach for maximizing the utility of individual boreholes drilled for mountain bedrock aquifer characterization.
Local Knowledge Graph (32 entities)
Related Works
Items connected by shared entities, co-authorship, citations, or semantic similarity.
Baseflow Age Distributions and Depth of Active Groundwater Flow in a Snow Dominated Mountain Headwater Basin
Constraining Bedrock Groundwater Residence Times in a Mountain System With Environmental Tracer Observations and Bayesian Uncertainty Quantification
Quantifying Subsurface Flow and Solute Transport in a Snowmelt-Recharged Hillslope With Multiyear Water Balance
Constraining Bedrock Groundwater Residence Times in a Mountain System with Environmental Tracer Observations and Bayesian Uncertainty Quantification: Modeling and Data Package
Groundwater and Surface Water Flow (GSFLOW) model files to explore bedrock circulation depth and porosity in Copper Creek, Colorado
Copper Creek Baseflow Age Experiment using Environmental Gas Tracers in the East River Watershed, CO.
Hydrogeology 101
25 Facts About Water in the San Luis Valley
Gunnison Basin Power
Cited By (20 times, 2 in Knowledge Hub)
References (66)
1 in Knowledge Hub, 65 external