Incipient Bed-Movement and Flood-Frequency Analysis Using Hydrophones to Estimate Flushing Flows on the Upper Colorado River, Colorado, 2019

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In an effort to better understand sediment movement and its relation to flow regimes of the Upper Colorado River in Colorado, in 2019, the U.S. Geological Survey, in cooperation with the Upper Colorado River Wild and Scenic Stakeholder Group, studied the magnitude and recurrence interval of streamflow (discharge) needed to initiate bed movement of gravel-sized and finer sediment in a segment of the Colorado River.

The study area extended from the confluence of the Blue and Colorado Rivers near Kremmling, Colorado, downstream to the confluence of the Eagle and Colorado Rivers near Dotsero, Colo.

Bed movement occurred more frequently at lower streamflows from State Bridge to Catamount Bridge compared to the study area upstream from State Bridge. As a result, the flushing flow was characterized in the study area using two definitions: the “upstream flushing flow” for locations above State Bridge and the “downstream flushing flow” for locations below State Bridge.

Stationary hydrophones upstream from the Catamount Bridge Recreation Area boat launch in Eagle County, CO

Stationary hydrophones that were connected to flexible conduit as they were mounted in the streambed. The two additional pieces of rebar installed upstream from the two hydrophones were to deflect debris. Photo location is upstream from the Catamount Bridge Recreation Area boat launch in Eagle County, Colorado.

(Credit: Michael Kohn, USGS. Public domain.)

Acoustic data from stationary hydrophones continuously deployed in the spring and summer of 2019 and longitudinal hydrophone acoustic profiles manually collected in summer 2019 were used to identify the streamflow needed for incipient gravel-bed movement and establish flushing flows defined for this study. The upstream flushing flow was defined as 3,000 cubic feet per second (ft3/s) at streamgage 09058000 Colorado River near Kremmling, Colo. (the Kremmling streamgage) based on the underwater acoustic data from the downstream location at the Radium stationary site (2,950 ft3/s at the Kremmling streamgage which was rounded to 3,000 ft3/s). The downstream flushing flow was defined as 2,400 ft3/s at the Kremmling streamgage or 3,100 ft3/s at streamgage 09060799 Colorado River at Catamount Bridge, Colo. (the Catamount Bridge streamgage) based on the more conservative streamflow associated with the flushing flow defined using underwater acoustic data from the downstream location at the above Catamount Bridge stationary site (2,310 ft3/s at the Kremmling streamgage which was rounded to 2,400 ft3/s and 3,040 ft3/s at the Catamount Bridge streamgage which was rounded to 3,100 ft3/s).

 

Research vessel with the mobile hydrophone system collecting acoustic data along the upper Colorado River

Research vessel with the mobile hydrophone system collecting acoustic data to determine the presence of bed movement along the upper Colorado River. Photo location is downstream from the Pump Recreation Area boat launch in Grand County, Colorado.

(Credit: Richard McDonald, USGS. Public domain.)

 

The annual series of peak-streamflow data at the Kremmling streamgage were used to estimate annual exceedance probability (AEP) streamflows to compare to the flushing flow. Results from the Denver Water Platte and Colorado Simulation Model were used to generate daily peak-streamflows for a future conditions scenario provided for this report.

  • The upstream flushing flow of approximately 3,000 ft3/s at the Kremmling streamgage has an AEP near 0.50 (2-year return period) depending on the period of historical record and an AEP near 0.43 (2.33-year return period) for the future period.
  • The downstream flushing flow of approximately 2,400 ft3/s at the Kremmling streamgage has an AEP near 0.67 (1.5-year return period) depending on the period of historical record and an AEP near 0.67 (1.5-year return period) for the future period.