Pocket project

A. Project description

  1. Deepen existing pockets and create new ones for the purpose of increasing water depth and volume.

  2. The pockets would be for trout refuge during periods of stream dewatering.

  3. Pockets refer to locations that have more depth and volume per unit length than elsewhere in the stream.

  4. They would not replace larger habitat for trout life-cycle needs, but would be for retreat during dewatering.

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Pocket refuge at Ryman created naturally from a fallen tree

B. Background

  1. Some pocket refuge exists already in streams, occurring naturally, as seen at Ryman, for example.

  2. Pockets develop from flow at in-stream structures that results in scouring of the streambed directly downstream.

  3. Typical in-stream structures are rocks and fallen trees.

  4. Pockets at Ryman also develop from placement of logs with a cutout that increases the flow velocity, causing scouring.

  5. While stream water temperatures were higher during 2018 drought conditions, as confirmed by statistical analysis...

  6. They did not exceed the Colorado chronic water temperature criterion for cold-water habitat.

  7. That is, even in dewatering, the Dolores tributaries stayed cold enough for native and wild trout species.

  8. The main stem's lower two-thirds, by comparison, was too warm during the drought, based on the chronic criterion.

  9. It is possible that tributaries can be cold-water refuge for main-stem trout seeking thermal relief in warm weather.

  10. So improved tributary pocket refuge could serve both tributary and main-stem trout population persistence.

C. Need and urgency

  1. The 2nd lowest-flow conditions, evidence of drought, in 67 years of records-keeping in the Dolores basin was in 2018.

  2. Only 2 years later, monsoon rains that historically occurred regularly were minimal and resulted in low stream flows.

  3. As the intensity and frequency of stream dewatering increases, which is reasonably expected, more refuge is needed.

  4. Additional refuge would figure in assisting native and wild trout populations to persist despite climate change.

D. Considerations

  1. Creation and enhancement, that is, improvement, of pocket refuge could be begun soon, requiring only simple tools.

  2. Actions would appear to avoid water rights issues since flow would not be interrupted.

  3. They would be compatible with installation of beaver dam analogs (BDAs) and post-assisted log structures (PALS).

E. Actions

  1. Set about with the necessary approval process for the simple actions contemplated.

  2. Identify the most appropriate streams for those actions and the specific locations within those streams.

  3. Proceed with the pocket refuge improvement, followed by monitoring and maintenance.

F. Details

a. Where

  1. Targets may be the largest streams, actions at which can improve the greatest amount of trout habitat.

  2. Also figuring in targeting may be streams where actions can be expected to be the most successful.

  3. That would be where pockets are most likely to maintain sufficient water for habitat despite drought.

  4. Those streams with that highest likelihood have the largest drainage areas and the highest maximum elevations.

  5. Important may be streams already demonstrated to have good food supply and known trout populations.

  6. Good candidate streams logically would be unlikely to have or develop water quality problems.

  7. It may include those with enough length for upstream, isolated habitat as part of cutthroat conservation.

  8. It may include streams with existing ponding, which can assist in maintaining downstream baseflow.

  9. It also could include those that are good candidates for other actions, such as BDA installations.

  10. A suggested start is at 5 streams, which range in outfall elevation from 8167 to 9603 ft.

  11. Likely good locations in streams for pocket projects are where width is constrained and elevation drop is high.

  12. They could have the most vertical scouring and the least unintended stream widening upstream of the structure.

  13. It likely is wise to begin the work at upstream locations where susceptibility to dewatering is greatest.

  14. Consideration, however, is necessary that upstream locations are not too high and cold for winter habitat.

  15. Natural mixing in stream flow appears to prevent localized temperature conditions, as observed by testing.

  16. Locations of continuous flow are best so pocket water does not overheat from ambient air and solar radiation.

  17. Shaded pockets may be more successful than unshaded ones during extreme drought when flow is least.

b. When

  1. The period of August to October possibly is best for conducting enhancement and creation of pocket refuge.

  2. The low-flow conditions during that time would enable useful observations about locations for the work.

c. Materials and equipment

  1. Materials for in-stream structures are trees, logs, and rocks available streamside.

  2. Equipment for installation are simple, portable tools like shovels, picks, saws, pry bars, winches, and chains.

d. Monitoring and maintenance

  1. Installations would be monitored for effectiveness, for example, a minimum depth of 1 ft at low flow, perhaps.

  2. Actions would be taken to maintain and improve effectiveness, for example, adding rocks for structural stability.

F. Supporting information

a. Example pockets

  1. Within the lower mile at Ryman are examples of naturally occurring and installed pockets, Exhibits 1 & 2.

  2. They demonstrate variety with logs, fallen and placed, and beaver structures, intact and not.

  3. A representative pocket volume observed was about 100 cu ft, or roughly 2 ft deep, 6 ft wide, and 8 ft long.

  4. It was equivalent to a 50-ft length of stream that was approximately 8 in deep and 3 ft wide.

  5. Ryman is small, potentially too small in habitat volume for a consequential pocket project.

b. Recent low-flow conditions

  1. Flow in the Dolores River basin in 2018 was the lowest in nearly 70 years of records keeping, Exhibit 3.

  2. In 2020, warm-weather flows were low again as a result of only small amounts of monsoon rainfall, Exhibit 4.

  3. The yellow triangles (below) show historical median flows; the jagged blue line, 2018 and 2020 observed flows.

  4. 2018 flows typically were one-third of historical values or lower; in 2020, always lower except briefly in late July.

c. Comparison of scouring and low-flow conditions

  1. High flow from snowmelt at Coal in May 2021 demonstrated a capacity for streambed scouring, Exhibit 5.

  2. Coal is the 10th largest in July-August flow of 42 perennial, trout-bearing streams in the Dolores basin.

  3. It is the 9th largest in drainage area and maximum elevation, marking relatively high resilience in flow.

  4. October 2020 flow conditions showed some vulnerability to dewatering, however, despite its size, Exhibit 6.

  5. With large habitat volume and comparatively high flow resilience, it is a potential candidate for a pocket project.

d. Largest streams by flow, drainage area, and maximum elevation

  1. The 10 largest of the 42 streams based on July-August flows are shown below, Exhibit 7.

  2. The 10 largest by highest maximum elevations and greatest drainage areas also are shown, Exhibit 8.

  3. It is evident that the largest flows correlate strongly with the highest drainage areas and maximum elevations.

  4. The 10 largest streams by volume and resilience, and candidates for proposal as Outstanding Waters, Exhibit 9.

  5. Those with stream protections existing or underway, cutthroat trout presence, and other features, Exhibit 10.

f. Example water quality

  1. Sampling at 9 of the 42 streams has given no evidence of dissolved metals problems in the streams, Exhibit 11.

  2. Runoff where grazing occurs can bring coliform and E. coli bacteria into streams, not surprisingly, Exhibit 12.

  3. Other parameter values in Exhibit 12 indicate satisfactory aquatic habitat, that is, no deviation from standards.

g. Exhibits

Exhibit 1. Example of pocket refuge at Ryman, developed from a fallen tree

Log placement

Pocket below log: depth, 2 ft; width, 5 ft; length, 5 ft.

Log: length, 22 ft; diameter, 1 ft; cutout width, 1 ft.

Note: The cutout on the top of the log concentrates the water's scouring effect on the streambed directly below. For comparison, long stretches of the stream were roughly 8 in deep and 3 ft wide.

Exhibit 12. Coliform and E. coli bacteria presence in streams that drain grazing areas
Exhibit 3. 2018 drought-condition flow compared with 67-year median daily flow
Exhibit 4. 2020 flow with little monsoon rainfall and 67-year median daily flow
Exhibit 5. At Coal, May 2021 high-flow conditions having streambed scouring potential
Exhibit 6. Low-flow, October 2020 conditions at Coal, a candidate for improved refuge
Exhibit 7. Ten of the 42 perennial, trout-bearing streams with largest July-August flows
Exhibit 8. Ten of the 42 streams with largest drainage areas and maximum elevations
Exhibit 9. Comparison of habitat volume, resilience, and other features at streams
Exhibit 10. Protections existing or in-process and other features
Exhibit 11. No evidence of dissolved metals problems from stream sampling

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Exhibit 2. Example of pocket refuge at Ryman from log placement

Fallen tree

Pocket below tree: depth, 2 ft; width, 5 ft; length, 5 ft.

Water above tree: depth, 1 ft.

Note: This is an example of pocket refuge that has occurred naturally from scouring directly downstream of a fallen tree.

Exhibit 12. Elevated total coliform & E. coli (in red) likely result from permitted grazing