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​Cold-water signal

  A. Background

  1. No resources were on hand in this study for assessing fish movement with radio telemetry.

  2. Instead, a portable temperature sensor was used to find if there were cold-water plumes in the main stem.

  3. This would be where cold-water tributaries discharged into it.

  4. If so, the plumes could signal to trout where cold-water relief was available.

  5. Results of limited testing are shown in the diagram below and described in the text that follows.

    Nearby | Movement | Signal

Cold-water plume in the main stem at Bear


  B. Testing​

  1. Using a hand-held sensor, water temperatures were determined at the discharge of three large tributaries.

  2. These were Bear, Roaring Forks, and Stoner, with measurements made on September 13, 2019.

  3. A cold-water plume was found where Bear flowed into the main stem.

  4. Water temperature in the plume was 3.3 F colder than the water nearby in main stem.

  5. This is depicted in the diagram above.

  6. The plume at Bear reached half-way across the main stem and was detectible 20 ft downstream.

  7. A smaller cold-water plume was found below Roaring Forks, extending 5-6 ft downstream in the main stem.

  8. No plume was found below the Stoner discharge.

  9. This was the case because Stoner's discharge temperature was warmer than the main stem.

  C. Conclusion​

  1. Where water entering the main stem from a tributary is colder, a cold-water plume may result.

  2. That cold-water plume may extend 5-20 ft downstream in the main stem.

  3. Do data show where there is a continuous presence of cold-enough water in the study area?

    Nearby | Movement | Signal

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