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Actions > Refuge

  • Natural processes leave refuge for trout.

  • That would be locations of deeper water while flow elsewhere is temporarily too shallow or lost.

  • It results from the tendency of water levels to rise directly upstream of across-channel structures.

  • And, more consequentially in volume, for plunge pools to develop directly downstream due to streambed scouring.

  • The scouring is most intense during seasonal runoff from snowmelt.

  A. Examples​

  • The plunge pool in exhibit 1 below the fallen tree was approximately 2 ft deep, 5 ft wide, and 5 ft long, or 50 cu ft.

  • In exhibit 2, the plunge pool was 2 ft deep, 6 ft wide, and 8 ft long, roughly 100 cu ft.

  • For comparison, the pool in exhibit 2 was equivalent in volume to 50 ft of stream length.

1. Fallen tree creating trout refuge

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2. Refuge from two fallen trees

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  B. Installation​

  • Additional refuge could be created from an organized placement of wood and rock structures.

  • They would be installed across the stream, bank to bank.

  • Structures would not be designed to flood water outside the stream channel.

  B. Installation​, cont.

  • They would be high enough to make some refuge upstream and to increase pourover momentum.

  • Shaping or a cutout would direct the pourover for maximum scouring.

  • A structure that arches upstream also could focus pourover, as shown below in exhibit 3.

  • Most streams in the study area have abundant wood and rock along their channels.

  • Structures would not be tall and would not seal, accommodating the passage of water and trout.

  • The tools necessary for installation are simple and portable.

3. Arched structure focusing scouring

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From Low-Tech Process-Based Restoration of Riverscapes, Pocket Field Guide, Utah State University, www.lowtechpbr.restoration.usu.edu.

  C. Preferences​

  • A preferred site results in a directly downstream body of water that is deeper and has an upstream bed slope that is steeper than at other sites.

  • That is, deeper in order to be the least likely place to go dry during dewatering conditions.

  • And a steeper upstream bed slope to bring more water momentum for scouring the streambed directly downstream of the structure.