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

Bypass Design and Juvenile Behavior Hydraulic Changes o 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 avoid o Flow Separation – always avoid o 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 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

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 Dissipation Rapidly move fish through this area Smooth 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 ft 3 = AWS flow, in ft 3 /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 valves Provide smooth pipes and joints Pipe 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 valves Provide smooth pipes and joints Pipe diameter – 10” minimum, but depends on bypass flow amount Flow velocity – keep fish and sediment moving through

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

Bypass Pipe

Bypass Energy Dissipation

Insert photo of rr bypass pipe and me

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) Alignment Avoid negative pressures No hydraulic jumps Sample facilities Access for inspection Properly compacted fill

Inspection

Bypass Conveyance System  General  Downwell design  Pipe criteria  Avoid pumping fish/bypass flow

Helical Pump

Bypass Outfall  Concerns Minimize predation Minimize disorientation of juveniles Minimize impact on adults Bypass releases into open channels which return to the river

Old White River Outfall

New White River Outfall

Bypass Outfall  Concerns  Submerged versus Elevated outfalls Advantages and Disadvantages Alternative design

Bonneville Dam Outfalls Old versus New

Bypass Outfall Concerns Submerged versus Elevated outfalls Design Criteria Ambient velocity >= 4 fps Minimize air entrainment (submerged outfall) Minimize predator holding areas (eddies) Maximum impact velocity = 25 fps Outfall egress Avian protection

Avian Lines

Bypass Outfall  Concerns  Submerged versus Elevated outfalls  Design Criteria  Energy Considerations Too much hydraulic head Too little hydraulic head Mid-range

Bypass Outfall Concerns Submerged versus Elevated outfalls Design Criteria Energy Considerations Bypass Outfall design options Locate close to point of diversion Locate in areas with sufficient flow Induced high ambient velocity Trade offs to hardening the outfall

Starbuck Outfall

Stanfield Outfall