Year Established: 2019 Start Date: 2019-03-01 End Date: 2020-02-29
Total Federal Funds: $4,992 Total Non-Federal Funds: $2,596
Principal Investigators: Michael Ronayne
Abstract: Problem: As bedrock aquifers in the Denver Basin undergo regional hydraulic head declines from longterm pumping (>50 m in some areas), preliminary evidence documents a transition to induced downward gradients and increased bedrock aquifer recharge. An evaluation using modeling and field data to quantify fluxes across stream, alluvial, and bedrock interfaces showed that long-term head declines can increase seepage below streams, increase bedrock aquifer recharge, and produce complex saturation conditions below stream channels, including a perched saturated zone in the alluvium underlain by an unsaturated region in the bedrock aquifer. These results warrant the collection of additional field data to evaluate fluxes deeper beneath the streambed to verify model predictions and refine our understanding of the stream, alluvial and bedrock responses to regional hydraulic head declines. An existing two-year data dataset supplemented with proposed data collection will allow for a robust analysis of fluxes below the streambed. Methods: Expand an existing shallow piezometer network along East Plum Creek in Douglas County by adding 3 additional, co-located, deeper piezometers equipped with temperature and pressure sensors. Analyze new and existing pressure and temperature data sets for three depths beneath the streambed using Darcy flux calculations and 1D heat transport modeling. Compare flux calculations for different methods and depths. Objectives: To qualitatively and quantitatively evaluate vertical fluxes beneath a losing streambed to investigate the persistence of downward fluxes in response to bedrock aquifer pumping. To refine our understanding aquifer and stream responses to regional bedrock aquifer pumping specifically with respect to induced bedrock aquifer recharge and groundwater-surface water exchange. Expected Outcome: Vertical gradients are expected to persist deeper beneath the streambed indicating a losing alluvial aquifer and induced bedrock aquifer recharge. Flux estimates will merit and constrain future modeling investigations which attempt to quantify groundwater-surface water exchange, interaquifer exchange, and bedrock aquifer recharge in the Denver Basin, an increasingly pumped, multiaquifer system with declining hydraulic heads.