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