Abstract Baseflow, a proxy for groundwater discharge to streams, is vital for sustaining streamflow in periods of drought or low overland flow. Current methods for estimating baseflow include tracer-based approaches, which employ measurements of electrical conductivity, hydrochemical tracers, or environmental isotopes, and non-tracer-based approaches, such as graphical separation or numerical modeling. This technical note presents a novel, physics-based method for estimating baseflow using publicly available groundwater well data. The methodology was applied to the Roaring Fork River watershed in the Upper Colorado River Basin, USA. Groundwater level observations from 89 wells in the Roaring Fork River watershed were obtained for a 21-year period to interpolate mean static groundwater elevations. Hydraulic gradients toward the Roaring Fork River were elucidated from groundwater level contours. Hydraulic conductivity estimates in the shallow alluvium aquifer along the Roaring Fork River were obtained from pumping test data in 82 wells. On the basis of the average hydraulic gradient and the hydraulic conductivity estimates, a baseflow contribution of 9.6 m 3 /s from groundwater discharge was derived. This baseflow estimate divided by the measured mean annual streamflow results in a baseflow index of 0.6 for the Roaring Fork River watershed, compared to a baseflow index of 0.82 from graphical separation. Although no universally accepted ground-truth method for baseflow estimation exists, this study introduces a novel approach using groundwater flow physics. Given the scarcity of reliable, larger-scale baseflow estimates, and the importance of quantifying baseflow for water resource management, this study highlights the potential applicability of often underutilized groundwater data for hydrologic studies.
Celupica-Liu et al. (Thu,) studied this question.