Controls on groundwater-surface water interaction in a glacial valley, northern Colorado
Date
2022
Authors
Doebley, Valerie, author
Ronayne, Michael, advisor
McGrath, Daniel, committee member
Kampf, Stephanie, committee member
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Abstract
In the last few decades, scientists determined that groundwater discharge may supply a significant portion of streamflow in mountain watersheds. However, difficulties with access and drilling typically limit the use of monitoring wells to study groundwater in high-elevation, mountainous catchments. The recent installation of two 10-meter-deep monitoring wells plus several riparian wells along the South Fork of the Cache la Poudre River at the Colorado State University Mountain Campus provided an opportunity for a unique hydrogeological study at a mountainous site. Data from these wells combined with numerical groundwater modeling helped quantitively and qualitatively characterize groundwater-surface water exchange along a ~2.7-km study reach. Analyses reveal complex temporal and spatial variation of gaining and losing stream conditions within the study reach. First, well water level elevations and groundwater modeling results indicate that the South Fork is generally gaining in the upper portion of the valley and losing near the downstream end. We suggest that valley geometry and channel planform influence the spatial differences in groundwater-surface water exchange along the study reach. Second, streamflow differencing and modeling results suggest that the study reach changes between overall gaining and overall losing stream conditions multiple times between May and October. We suggest that these temporal variations in groundwater-surface water exchange are driven by seasonal changes in surface water contributions to streamflow and evapotranspiration. Third, stable isotope (δ2H, δ18O) analyses and groundwater modeling results suggest that localized recharge from moraine ponds and stream leakage are important sources of aquifer recharge. These results indicate that groundwater and surface water at the Mountain Campus are highly interdependent, and that any disturbances that impact surface water contributions to streamflow may ultimately impact the groundwater contributions as well.
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Subject
groundwater-surface water exchange
groundwater modeling
mountain hydrogeology