Characterization of Streamflow, Suspended Sediment, and Nutrients in the Upper Yampa River Basin

The UYRB is defined as the reach of the Upper Yampa River drained by the Yampa River Watershed between Craig, Colorado and its headwaters near the Flat Top mountains. The basin is primarily located within Routt and Moffatt Counties, which contain the cities of Craig and Steamboat Springs and towns of Hayden, Oak Creek, and Yampa. Major economic activities include agriculture (cattle production), mining, recreation and tourism.

In 2012, the U.S. Geological Survey published a retrospective analysis of the UYRB which documented water-quality conditions in the region. The report was useful in establishing baseline conditions and demonstrating that water in rivers and streams of the UYRB was generally of very good quality. An in-depth analysis of how land-use and climate were influencing the observed water-quality conditions was not possible primarily due to a lack of streamflow data, which is needed for this type of assessment. Because of this data gap, the USGS and local stakeholders established a more comprehensive long-term water-quality monitoring program for the UYRB. The monitoring program has been in place since October of 2010. Sites included in the monitoring program were selected to represent different geologic and land-use types in the UYRB.

In recent years, new interim state regulations for nutrients (Colorado Department of Public Health & Environment Regulation #31) and concerns related to algae blooms in Stagecoach Reservoir have become important topics to local stakeholders. Concerns are centered around the possible exceedance of new nutrient standards and the impact any observed increases in nutrient levels might have on existing water supplies (for example, increases in algae). Nuisance algae blooms have been observed with increasing frequency in the past several years (2015-18) in Stagecoach Reservoir and to some extent, as reported anecdotally from residents and land managers, in the mainstem of the Yampa River. Direct and indirect effects of land-use, hydrology, and climate change can exacerbate conditions that favor bloom-forming algae (i.e., excess nutrients and warmer temperatures). This study, in cooperation with local stakeholders in the UYRB water community, was initiated in 2019 to characterize streamflow, suspended sediment, and nutrients using historic (where available) and more recently acquired water-quality data from the long-term monitoring program initiated in 2010.

The objectives of this study were to:

• characterize available water-quantity and water-quality data
• Identify seasonal and spatial variability in water quantity and water quality
• Provide comparisons to interim State nutrient standards
• Estimate long-term trends in streamflow, suspended sediment, and nutrient concentrations and loads where data exist
• Provide a summary of data related to algae blooms collected from Stagecoach reservoir
• Assess how changes in land-use activities, population, and water consumption relate to streamflow, water-quality, and nutrient trends,
• Compare the findings from this study to other peer reviewed literature in regards to algae blooms and water quantity and quality.