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Design of Bypass Systems

Design of Bypass Systems. Special thanks to Ed Meyer, who provided the framework for most of these slides. Introduction. Goal #1: The Bypass must return fish quickly and safely to the river.

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Design of Bypass Systems

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  1. Design of Bypass Systems Special thanks to Ed Meyer, who provided the framework for most of these slides

  2. Introduction • Goal #1: The Bypass must return fish quickly and safely to the river. • Goal #2: The Bypass must effectively prevent debris and sediment from disrupting flow into and through the bypass system.

  3. Introduction • To accomplish these Goals, the screen and bypass must be designed to work hydraulically in tandem. • A vigilant operations and maintenance plan must be in place to maintain these design conditions.

  4. Screen and Bypass – Basic Layout

  5. Bypass Design • Optimum Design Combines: • Biology - incorporates behavior and swimming ability. • Engineering - “smooth and open” structural components that avoid abrupt light and hydraulic transitions and provide clear migration paths. • Hydraulics – match design with behavior traits and swimming ability.

  6. Bypass Design • Optimum Design Anticipates: • Hydrology – must provide adequate protection for fish and civil works for any flow condition. • Operations – must allow simplest operations possible for given site conditions and constraints. • Maintenance – must allow for efficient debris and sediment management.

  7. Swimming Speed Ability • Factors in Bypass Avoidance / Attraction • Sustained speed (minutes) • Length of screen • Number of bypasses required • Design for adverse water quality

  8. Bypass Design and Juvenile Behavior • Lighting Conditions • Intensity • Mercury Vapor Lights • Strobes • Clean Surface / Turbidity • Avoid Darkness

  9. Dark Entrance

  10. Dark Entrance

  11. Bypass Design and Juvenile Behavior Hydraulic Changes • Acceleration should be less than 0.1 fps per foot (or 1 ft/s in 10 feet of travel). (NWFSC tests at McNary) • Deceleration – always avoid • Flow Separation – always avoid • Eddys – always avoid

  12. Bypass Design and Juvenile Behavior • Risks to Bypass Avoidance and Holding • Low velocity zones (predators) • Delayed Migration (smoltification) • Entrainment (through screens) • Impingement (on screens)

  13. Bypass Design and Juvenile Behavior Conclusion – design features to avoid: • Vertical wall and floor offsets - use tapers if necessary, but should not usually be necessary • Abrupt light transitions • Poor hydraulic conditions

  14. Screens that may not require a formal bypass: • River bank screens • End of pipe screens • Trap and haul

  15. River Bank Screen Construction

  16. River Bank Screen Completed

  17. “Torpedo” style screen

  18. Fixed drum screen – Priest Rapids

  19. Features to note: easily retrievable , deep location, spray bar to move debris

  20. Components of the Bypass System • Entrance • Conveyance System • Outfall

  21. Bypass Entrance

  22. Bypass Entrance

  23. Bypass Entrance • Bypass Flow • Bypass flow should use from 5% to 10% of diverted flow. • Bypass flow amount should be chosen to achieve all hydraulic objectives: • No flow deceleration • Limited flow acceleration (0.1 to 0.2 fps per foot) • Bypass pipe flow depth • Move sediment and debris

  24. Bypass Entrance • General • Use grated or open-topped bypass entrance (including downwell). • Provide access for inspection and debris removal • Maintain 1.5 or 2 ft bypass width – bigger is better. • Full depth bypass slot required for large screens, but smaller screens (less than 10 cfs or so) seem to work well with an orifice entrance (6” minimum into a 10” pipe) or ramped weir (Batelle tests).

  25. Bypass Entrance • General • Minimum depth over bypass weir is 1 ft • Can use bypass ramp to gradually increase velocity. • Secondary screen dewatering – used to maintain velocity. • Consider PIT detector installation

  26. Old Screen Design - Bypass Entrance

  27. Full Depth Slot vs.

  28. Intermediate Bypass

  29. Intermediate Bypass

  30. Secondary Screens / Pumpback

  31. Secondary Screening

  32. Bypass Entrance and Secondary Screens at Upper Baker

  33. Small Rotating Drum Screen – Bypass Entrance

  34. Baker Lake Bypass

  35. Break

  36. Bypass Conveyance System • Downwell design objectives: • Energy Dissipation • Rapidly move fish through this area • Smooth transition to bypass pipe entrance

  37. Energy Dissipation in the Downwell A bypass downwell should have a minimum water volume established by the following formula: where: = unit weight of water, 62.4 pounds (lb) per ft3 = AWS flow, in ft3/s = energy head (water surface to water surface), in feet

  38. Bypass Cross Section

  39. Bypass Downwell

  40. BIG bypass downwell (Wanapum)

  41. Bypass Conveyance System • Bypass Pipe criteria • Full pipe or open channel flow? Depends. • Avoid closure valves • Provide smooth pipes and joints • Pipe diameter – 10” minimum, but depends on bypass flow amount • Flow velocity – keep fish and sediment moving through

  42. Bypass Conveyance System • Bypass Pipe criteria • Full pipe or open channel flow? Depends. • Avoid closure valves • Provide smooth pipes and joints • Pipe diameter – 10” minimum, but depends on bypass flow amount • Flow velocity – keep fish and sediment moving through

  43. Bypass Conveyance System • Bypass Pipe material • PVC • Spun mortar in steel • HDPE • CMP – specific types, not all • Roughened channel – If excess energy

  44. Bypass Pipe

  45. Bypass Pipe

  46. Bypass Energy Dissipation

  47. Bypass Energy Dissipation

  48. Insert photo of rr bypass pipe and me

  49. Bypass Pipe Joints

  50. Bypass Pipe Joints • Use well compacted fill material in pipe trench. • Avoid any protruding joint design, especially those that can catch debris.

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