Design of Bypass Systems
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Transcript of 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.
Goal #2: The Bypass must effectively prevent debris and sediment from disrupting flow into and through the bypass system.
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.
Screen and Bypass – Basic Layout
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.
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.
Swimming Speed Ability
Factors in Bypass Avoidance / Attraction○ Sustained speed (minutes)○ Length of screen○ Number of bypasses required○ Design for adverse water quality
Bypass Design and Juvenile Behavior
Lighting Conditions○ Intensity○ Mercury Vapor Lights○ Strobes○ Clean Surface / Turbidity○ Avoid Darkness
Dark Entrance
Dark Entrance
Bypass Design and Juvenile Behavior
Hydraulic Changeso Acceleration should be less than 0.1 fps per
foot (or 1 ft/s in 10 feet of travel). (NWFSC tests at McNary)
o Deceleration – always avoido Flow Separation – always avoido Eddys – always avoid
Bypass Design and Juvenile Behavior
Risks to Bypass Avoidance and Holding○ Low velocity zones (predators)○ Delayed Migration (smoltification)○ Entrainment (through screens)○ Impingement (on screens)
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
Screens that may not require a formal bypass:
River bank screens End of pipe screens Trap and haul
River Bank Screen Construction
River Bank Screen Completed
“Torpedo” style screen
Fixed drum screen – Priest Rapids
Features to note: easily retrievable , deep location, spray bar to move debris
Components of the Bypass System
Entrance Conveyance System Outfall
Bypass Entrance
Bypass Entrance
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
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).
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
Old Screen Design - Bypass Entrance
Full Depth Slot
vs.
Intermediate Bypass
Intermediate Bypass
Secondary Screens / Pumpback
Secondary Screening
Bypass Entrance and Secondary Screens at Upper Baker
Small Rotating Drum Screen – Bypass Entrance
Baker Lake Bypass
Break
Bypass Conveyance System
Downwell design objectives:Energy DissipationRapidly move fish through this areaSmooth transition to bypass pipe
entrance
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
Bypass Cross Section
Bypass Downwell
BIG bypass downwell (Wanapum)
Bypass Conveyance System Bypass Pipe criteria
Full pipe or open channel flow? Depends.Avoid closure valvesProvide smooth pipes and jointsPipe diameter – 10” minimum, but depends
on bypass flow amount Flow velocity – keep fish and sediment
moving through
Bypass Conveyance System Bypass Pipe criteria
Full pipe or open channel flow? Depends.Avoid closure valvesProvide smooth pipes and jointsPipe diameter – 10” minimum, but depends
on bypass flow amount Flow velocity – keep fish and sediment
moving through
Bypass Conveyance System Bypass Pipe material
PVCSpun mortar in steelHDPECMP – specific types, not allRoughened channel – If excess energy
Bypass Pipe
Bypass Pipe
Bypass Energy Dissipation
Bypass Energy Dissipation
Insert photo of rr bypass pipe and me
Bypass Pipe Joints
Bypass Pipe Joints Use well compacted fill material in pipe
trench. Avoid any protruding joint design,
especially those that can catch debris.
This 25’ long rootball grew through a misaligned bypass pipe joint.
Bypass Conveyance System Pipe criteria (con’t)
AlignmentAvoid negative pressuresNo hydraulic jumpsSample facilitiesAccess for inspectionProperly compacted fill
Inspection
Inspection
Bypass Conveyance System
General Downwell design Pipe criteria Avoid pumping fish/bypass
flow
Helical Pump
Bypass Outfall
ConcernsMinimize predationMinimize disorientation of juvenilesMinimize impact on adultsBypass releases into open channels
which return to the river
Old White River Outfall
New White River Outfall
Bypass Outfall
Concerns Submerged versus Elevated
outfallsAdvantages and DisadvantagesAlternative design
Bonneville Dam OutfallsOld versus New
Bypass OutfallConcernsSubmerged versus Elevated outfallsDesign Criteria
Ambient velocity >= 4 fpsMinimize air entrainment (submerged outfall)Minimize predator holding areas (eddies)Maximum impact velocity = 25 fpsOutfall egressAvian protection
Avian Lines
Avian Lines
Bypass Outfall Concerns Submerged versus Elevated outfalls Design Criteria Energy Considerations
Too much hydraulic headToo little hydraulic headMid-range
Bypass Outfall
ConcernsSubmerged versus Elevated outfallsDesign CriteriaEnergy ConsiderationsBypass Outfall design options
Locate close to point of diversionLocate in areas with sufficient flowInduced high ambient velocityTrade offs to hardening the outfall
Starbuck Outfall
Stanfield Outfall