Characterization of Groundwater Flow at a Mountainous Watershed, Niwot Ridge, Front Range, Colorado
Monday, May 5, 2014: 3:20 p.m.
Blake (Westin Denver Downtown)
Sarah Evans
,
Geological Sciences, University of Colorado, Boulder, CO
Shemin Ge
,
Geological Sciences, University of Colorado, Boulder, CO
We present a 3D coupled flow and solute transport hydrogeologic model for the Niwot Ridge Watershed in the Front Range of Colorado. This is the first 3D modeling attempt at detailing groundwater recharges at this site. The 7.6 km
2 watershed ranges in elevation from 3241 to 4082 m and is representative of an alpine setting. Its climate is characterized by a mean annual precipitation of 1.95 m, mean annual air temperature of -2.1ºC, and extensive snow coverage six months of the year with 80% of the precipitation falling as snow. In the middle of the watershed are six paternoster lakes connected by North Boulder Creek, the headwaters of the South Platte River. We use a transient flow and steady state solute transport 3D finite element model to characterize the groundwater and solute transport systems and quantify mountain recharge under averaged long-term conditions.
Field data including effective porosity, hydraulic conductivity, and solute concentration in surface water are utilized to constrain and calibrate model parameters. Preliminary model results indicate that regional groundwater flow is from northwest to southeast, towards North Boulder Creek. This groundwater flow pattern is consistent with field observations. The average hydraulic head gradient over the entire modeled area is approximately 0.12 m/m. Groundwater velocity varies from 1.4 × 10-6 to 1.8 × 10-3 m/s. Groundwater flow is primarily driven by a topographically influenced precipitation regime, with 7% of the total precipitation recharging into the subsurface. Modeled baseflow oscillates annually, with peak baseflow occurring after peak snowmelt runoff. Groundwater contribution to baseflow of North Boulder Creek is at an average rate of 0.03 m3/s or 23% of streamflow, which is on the same magnitude as observed values. Modeled discharge solute concentration (Na+) output values corroborate with observed surface water values, increasing with a decrease in elevation.
Sarah Evans, Geological Sciences, University of Colorado, Boulder, CO
Sarah Evans received her M.S. in geological sciences from the University of Colorado in 2013 and B.A. in geology and environmental studies from Whitman College in 2011. She is currently working toward her Ph.D. in geological sciences in the Department of Geological Sciences at the University of Colorado at Boulder. Her research interests include headwater catchments and water resource management.
Shemin Ge, Geological Sciences, University of Colorado, Boulder, CO
Shemin Ge is a professor of geology at the University of Colorado at Boulder. Her areas of research include fluid flow and contaminant transport in fractured porous media, fluid flow and rock deformation, and water resource management. Ge earned her Ph.D. from Johns Hopkins University and is currently managing editor of Hydrogeology Journal.
