1. Small-Scale Fish Screen Selection Workshop
Brent Mefford, P.E. – Wild Fish Engineering
Bryan Heiner, P.E. – U.S. Bureau of Reclamation
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

2. Why Screen? Fish screening can serve multiple objectives:
Fish Protection
Debris Management
Sediment Management
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

3. Fish Protection
Preventing fish from being entrained or injured by diversion of flow from a stream, lake or canal.
Positive Barrier: exclude all aquatic organisms larger than the screen hole size.
Behavior Barrier: guide fish away from diversions using louvers, bar rack, sound, light, electricity, air bubbles curtains or a combination of these. - Does not exclude all fish.
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

4. Debris Management
To operate properly, a screen MUST BE designed to manage the inflow of debris.
Exclude Debris from the diversion, leaving it in the stream/lake.
Pass Debris entrained by the diversion downstream with the screened water.
Remove Debris from the diverted water and collect it onsite.
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

5. Sediment Management
Screens can be designed to aid in the management of sediment moving with the diverted water.
Larger bed sediments (bedload): roll along the channel bottom. Typically sand & gravel.
Finer suspended sediment: fine sand, silt and clay that are suspended and carried within the water as a mixture.
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

6. Screen Basics – Va & Vb
Approach Velocity (Va) – flow velocity measured perpendicular to the screen surface.
Should be less than the fish’s sustained swimming ability.
Sweeping Velocity (Vs) – flow velocity measured parallel to the screen surface.
Should be larger than Va to allow fish and debris the be swept away from the diversion flow. Va Vc Vs
SCREEN
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

7. Screen Basics – Velocity Ratio
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

8. Screen Basics - Baffles
Baffles are often required to ensure that even approach velocities across the entire screen area are achieved.
Screen
Baffles
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

9. Screen Basics – Approach Flow
Approach Channel Flow
It is important to have a uniform flow entering the screen area to prevent unwanted impingement zones
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

10. Screen Basics - Location
In-Ditch In-Stream/Lake
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

11. Screen Basics – In-Ditch
In-Ditch Pros:
Ease of dewatering the screen for inspection & maintenance
Flow conditions are typically more predictable & controlled
In-Ditch Cons:
Requires fish bypass
Requires more water at the stream/lake diversion
Bypassed fish are more susceptible to predators
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

12. Screen Basics – In-Stream
In-Stream/Lake Pros:
No fish enter diversion
No fish bypass required
In-Stream/Lake Cons:
Maintenance access may be difficult or limited
Screen may need to be removed during freezing weather
Large debris may damage screen
Flow conditions may be highly variable
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

13. Screen Basics – Material
Fish screens are designed with a metal frame and a screen fabric.
Screen Porosity: % open area of the screen.
Headloss: drop in water surface or pressure across the screen.
Hole Size: important to consider to meet criteria based on life stage & debris loading (several X smaller or larger than dominant debris).
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

14. Screen Basics – Woven Wire
Woven Wire Screen:
Low cost
Requires closely spaced supports
Can be difficult to clean
Square or rectangular openings
Creates a rough surface
Best where debris loads are light
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

15. Screen Basics – Perforated Plate
Perforated Plate Screen:
Low cost
Can requires closely spaced supports
Smooth surface
Round openings
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

16. Screen Basics – Wedge-Wire
Wedge-Wire Screen:
Smooth upstream face
Expanding orifice opening in profile
Requires minimal support structure
Durable
Expensive
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

17. Screen Basics – Tilted Wedge-Wire
Wedge-Wire Screen:
Smooth upstream face
Expanding orifice opening in profile
Requires minimal support structure
Durable
Expensive
Can pass more flow
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

18. Screen Basics – Other Types
Many modeled or woven fabrics are available in synthetic materials
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

19. Screen Basics – Cleaning
All fish screens require periodic maintenance but will reduce downstream maintenance if designed appropriately.
Cleaning methods available:
Back-flush
Mechanical
Natural
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

20. Screen Basics – Back-flush
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

21. Screen Basics – Back-flush
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

22. Screen Basics - Mechanical
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

23. Screen Basics - Mechanical
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

24. Screen Basics - Natural
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop

25. Screen Basics - Conclusion
The basics of screening offer many different options for designing screens.
Many times even after considering all the options screens are still a trial and error process and some modifications/changes may be required after a screen is installed.
Questions?
August 2014
Clark Fork Coalition - Small-Scale Fish Screen Workshop