7845

• UCREFRP Catalog Number: 7845
• Author: Miller, W. J. and D. Laiho.
• Title: Final Report, Upper Colorado River Basin Recovery Implementation Program, Feasibility Evaluation Of Non-Native Fish Control Structures.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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recruitment to the in reservoir population. However, timing drawdowns to be effective can be
difficult.
3. Management of non-natives by harvest could be used in the stream and the reservoir for removal
of non-natives. This option, though, would not result in 100% removal and there would still be
non-native fish that persist. Mechanical removal has been used in several areas but there is not
enough data to show what impact removal of non-natives has on those populations.
1.3.8.2 Other Structures Found But Not Directly Applicable
In the process of the literature review and interviews, a number of passage exclusion structures were
identified which were either too experimental, non-applicable, impractical, or for which too little
information exists. They deserve some mention herein for comprehensiveness and for reference.
1. Granular filters: Filtering through granular berms or beds; similar to rapid sand filters of water
and wastewater filtering systems.
2. Resistance board weir: A downstream sloping weir fixed at the bottom, angling up and held up
by the resistance of a surface resistance board; primarily used to prevent adult fish (salmon) from
moving upstream, but could be applied similarly to a net in a spillway approach area.
3. Hanging fingers: Rods hung from above into a fixed, partly submerged bar rack keeps adult fish
from passing up- and downstream, but allows debris to occasionally flush through by pushing
fingers downstream, with the fingers falling back to their original position.
4. Hanging chains: Similar to hanging fingers, but hung from a surface superstructure to the
waterway bottom or a pre-selected depth.
1.3.8.3 Other Behavioral Techniques Found But Not Directly Applicable
Other behavioral barriers exist which can restrict (repel), attract away, or direct movement away.
These are mostly experimental, highly or variably selective or most effective in combination with
other behavioral or physical barriers. Some include:
1. Temperature curtains: Impermeable geotextile material suspended from surface flotation devices
to block the flow of warm water to outlet structures, thereby excluding warm water fish. A
natural variation of a temperature curtain is to simply place the outlet very deep (>100 feet
deep).
2. Vibration: Indirect or secondary (trash rack vibration induced by flow) or intentional, artificially
generated pressure waves sensed by a fishes inner ear or lateral line can trigger an avoidance
reaction.
3. Entrained and bubble curtains: Natural (turbulent flow air entrainment) or artificial (diffused air
bubbles) creates a visual barrier. Some fish are attracted to bubble areas, but don't pass.
Possible need to keep open, still water on both sides of curtain.
4. Turbidity/optical dispersion curtain: A visual barrier of refracted light (light noise).
5. Turbulence: Water jets directed up from the bottom by pumps to create water shear boundary
layer avoided by fish.
6. Combinations: Combinations of physical and behavioral barriers can provide very effective
movement restrictions; for example, it was discovered somewhat by accident that high velocities
through a bar rack screen can cause screen vibrations and turbulence that acts as a behavioral
barrier and results in higher fish exclusion than can be achieved by the bar rack alone.
Control Structure Feasibility Evaluation
Miller Ecological Consultants, Inc., February 18, 1997
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