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The vitality of the Colorado River faces uncertainty in light of frequent and prolonged droughts induced by climate change. Progressing knowledge concerning the role of groundwater and surface water interactions is critical in informing water resource managers and Colorado River water users—namely, the mechanism of baseflow accounts for a substantial portion of streamflow. Baseflow is considered a proxy for groundwater discharge to streams. Groundwater is vital in sustaining streamflow via baseflow, particularly during periods of low precipitation and overland flow. Limited baseflow studies within the Upper Colorado River Basin indicate that approximately half of streamflow is accounted for by baseflow. This study aims to quantify baseflow to the Roaring Fork River, a major tributary within the Upper Colorado River Basin. The Roaring Fork River flows along the western margins of Colorado’s Southern Rocky Mountains physiographic province.

This study employed a new approach based on groundwater level data from the Colorado Division of Water Resources (CDWR). Groundwater level observations were compiled between 2000 and 2022 from over 150 wells in the Roaring Fork subbasin to ultimately interpolate static groundwater level elevations. Hydraulic gradients near the Roaring Fork River were elucidated from contoured groundwater levels. Existing estimates of hydraulic conductivity were analyzed using empirical pumping test formulae. On the basis of hydraulic gradient and hydraulic conductivity, a mean annual groundwater discharge of 1.57 m3/s to the Roaring Fork River is estimated. In parallel, baseflow separation using a graphical method was conducted, which yields a similar magnitude of baseflow. This study, for the first time, demonstrates the potential of utilizing existing groundwater level data to supplement the study of baseflow. Enriching the arsenal of baseflow analysis will help contribute to sustainable and informed water resource management.