Quantifying Baseflow Using Groundwater Levels in the Upper Colorado River Basin

Ayres, Nicholas L

Undergraduate Honors Thesis

Quantifying Baseflow Using Groundwater Levels in the Upper Colorado River Basin Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/d217qr233

Abstract

The vitality of the Colorado River faces significant 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 ultimately easing tension among 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. Previous baseflow studies within the Upper Colorado River Basin discern that more than 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 an 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 averaged hydraulic gradient and hydraulic conductivity, a groundwater discharge of 1.57 m³/s to the Roaring Fork River is estimated. In parallel, baseflow separation via a graphical method was conducted, which yields a similar magnitude of baseflow to that of the groundwater level approach. 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.

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