PASSAGE DESIGNS AT LOW HEAD BARRIERS

Bryan Nordlund, P.E.

Fish Passage Engineer

National Marine Fisheries Service

Lacey, WA

FISH PASSAGE ENGINEERS - 
THE BEGINNING

UPSTREAM PASSAGE DESIGNSDescription and Purpose !! A fish ladder converts the water surface elevation drop at a

passage impediment into passable increments while also providing suitable conditions for fish to safely hold, rest, and ultimately volitionally pass upstream. !

! Trap and haul is used to provide passage over tall dam(s), via ladder passage, collection by trap, thru sorting and handling facilities, followed by transport and release above tall barrier(s). !

! Either passage scheme involves design of a fish ladder with similar design features.

CONCRETE FISH LADDERS!Concrete fish ladders provide passage by utilizing a series of

fishway weirs to divide the total drop into a series of pools with equal and easily passable jumps, or passable swim thru conditions.

!!Examples of concrete fish ladders include:

▪ Vertical slot, ▪ Pool and weir, ▪ Weir and orifice, ▪ Pool and chute.

NON-CONCRETE FISH LADDERS!Non-concrete fish ladders accomplish passage by producing

energy dissipation along a channel with roughening elements, and passing fish either by a single burst or by a series of jumps.

!!Examples of non-concrete fish ladders include:

▪ denil/steeppass, ▪ roughened channels, ▪ stream simulation, ▪ log weirs, ▪ boulder weirs.

FISH LADDER – BASIC DESIGN CRITERIA 
(FOR ADULT STEELHEAD & SALMON)

! Hydraulic Drop: Maximum drop between ladder pools should be one foot or less for Pacific salmon, and less than the velocity head equivalent of the minimum burst swim speed for other species. !

! Flow Depth: Fishway overflow weirs should be designed to provide at least one foot of flow depth over the weir crest. !

! Pool Dimensions: The pool dimensions should be a minimum of 8 feet long (upstream to downstream), 6 feet wide, and 5 feet deep. However, some ladder designs require different dimensions, depending ladder style and flows.

Pool Volume: 

Important for energy dissipation, establishing a migration path, holding, staging and jumping/burst swim past next weir. 

This pool volume provides assumes the entire pool has active flow and contributes to energy dissipation. 


3)4())()((ftslbsft

HQV−

=γ

!

where: V = minimum pool volume, in ft3 !γ = unit weight of water, 62.4 pounds (lb) per ft3 !Q = fish ladder flow, in ft3/s !H = energy head of pool-to-pool flow, in feet

VERTICAL SLOT LADDER

(Photo courtesy of Thad Mosey, Biologist, Chelan PUD)

VERTICAL SLOT LADDER
!The vertical slot configuration is widely used for the

passage of salmon and steelhead. !

!The passage corridor typically consists of 1.0 to 1.25 foot-wide vertical slots for adult salmon, although narrower slots have been for smaller fish species. !

!The vertical slot ladder is suitable for sites which have tailrace and forebay water surface elevations that fluctuate somewhat, on the order of 10% of the total hydraulic drop.

!!Vertical slot ladders require fairly intricate forming for

concrete placement and very specific geometry.

STANDARD VERTICAL SLOT FISHWAY POOL GEOMETRY

Demonstration of flow patterns in a vertical slot fish ladder

(Photo courtesy of Melissa Jundt, NMFS)

ICE HARBOR LADDER AT WELLS DAM

(Photo courtesy of Tom Kahler, Biologist, Douglas PUD)

ICE HARBOR WEIR AT WANAPUM DAM

(Photo courtesy of Eric Lauver, Biologist, Grant PUD)

WEIR AND ORIFICE

Design Constraints !Weir and orifice ladders cannot accommodate much, if any,

water surface elevation fluctuation in the forebay pool. !

!When fluctuation of water surface elevation outside of the design elevation occurs, too much or too little flow enters the fishway. !

!This can be accounted for by add-in diffusers

WEIR AND ORIFICE FISH LADDER EXAMPLE – ICE HARBOR FISH LADDER

!The Ice Harbor fishway weir consists of two orifices, centered and directly below two weirs. !

! These orifice and weir combinations are located on each side of the longitudinal centerline of the ladder. !

!Between the two weirs is a slightly higher non-overflow wall, with an upstream projecting flow baffle at each end.

ICE HARBOR FISHWAY WEIR CROSS-SECTION

ICE HARBOR FISHWAY PLAN VIEW

ICE HARBOR FISHWAY CROSS-SECTION

HALF ICE HARBOR

!An adaptation of the Ice Harbor design for lower ladder flow is the Half Ice Harbor ladder design, which consists of one weir, one orifice, and a non-overflow wall between fishway pools.

HALF-ICE HARBOR WEIR, RIVER MILL LADDER, CLACKAMAS RIVER, OR

Photo courtesy of Peter Christensen, Design Engineer, R2 Resource Consultants

CUSHMAN DAM PASSAGE 
– TRAP AND HAUL USING A TRAM

GENERAL TRAP DESIGN SCHEMATIC

TURBINE DRAFT TUBE DIFFUSER

CUSHMAN II – FISHWAY AND TRAP CONSTRUCTION

POOL-CHUTE FISH LADDER!A pool and chute fishway is a hybrid type of fishway which

operates with different flow regimes under different river conditions. !

!This fishway is designed to operate as a pool and weir fishway at low river flows and a baffled chute fishway at higher river flows.

POOL-CHUTE FISH LADDER!This fishway offers an alternative for sites that have fairly low

hydraulic drop, and must pass a wide range of stream flows with a minimum of flow control features. !

!Placement of stoplogs, a cumbersome and potentially hazardous operation, is required to optimize operation. However, once suitable flow regimes are established, the need for additional stoplog placement may not be required. !

!Criteria for this type of fishway design are still evolving, and design proposals should be assessed on a site-specific basis.

POOL AND CHUTE LADDER SCHEMATIC

POOL AND CHUTE LADDER 

(SOMEWHERE IN CA)

ROUGHENED CHUTES

Description !Consists of a hydraulically roughened channel with near

continuous energy dissipation throughout its length. !

!Three examples of a roughened chute passage are a baffled chute (including steeppass and Denil fishways), roughened channels or stream simulation, and full width stream weirs.

FULTON DAM - BEFORE

FULTON ROUGHENED CHANNEL

CHEWUCH ROUGHENED CHANNEL

DENIL AND STEEPPASS !Denil and steeppass fishways are examples of roughened chute

fishways and are of similar design philosophy. !

!These fishways have excellent fish attraction characteristics when properly sited and provides good passage conditions using relatively low flow amounts.

DENIL AND STEEPPASS !Used mainly for sites where the fishway can be closely

monitored and maintained, such as off-ladder fish trap designs or temporary fishways used during construction of permanent passage facilities. !

!Because of their baffle geometry and narrow flow paths, Denil and steeppass fishways are especially susceptible to debris accumulation. !

!Not to be used for downstream passage, or lamprey passage. !

!Minor amounts of debris can restrict fish passage.

RIVER MILL DENIL LADDER, USED DURING LADDER CONSTRUCTION

(Photo courtesy of Peter Christensen, Design Engineer, R2 Resource Consultants)

RIVER MILL DENIL LADDER, USED DURING LADDER CONSTRUCTION

(Photo courtesy of Peter Christenson, R2 Engineering)

GENERAL DETAIL OF A DENIL LADDER

FULL STREAM WIDTH POOL AND WEIR LADDER (SOMEWHERE IN OREGON)

COOK WEIR – STILLAGUAMISH R

COOK WEIR – STILLAGUAMISH R

FULL WIDTH STREAM WEIRS

! Span the entire width of the stream channel and convey the entire stream flow. !

! incrementally step down the water surface elevation from the barrier to intersect the natural stream gradient downstream.

!!not a great deal of design or operational complexity.

Design notes: 1) Size notch to flow full with minimum instream flow. 2) Size pools for minimum volume of 16xQxH, (volume in cubic feet, Q (flow) in CFS and H (drop) in feet).

FULL WIDTH STREAM WEIRS – 
BASIC DESIGN

!Design of each weir concentrates flow toward the stream thalweg.

!Design provides a slight weir crest elevation decrease from

each bank to the center flow notch, and one foot drop from pool to pool.

!! Flow notch is designed to pass the minimum instream flow. !

!Higher stream flows pass over the entire weir crest. Natural bedload movement will fill in pools, usually scouring a good jump pool below the flow notch.

FULL WIDTH STREAM WEIRS – 
CAUTIONS! These have been constructed from reinforced concrete, boulders

or logs – but material needs to fit the site flow dynamics.

!! Boulders must be large, and logs must be properly embedded and

anchored to be stable – sometimes hard to find a source.

!! Boulders designs can have difficulty achieving the desired water

surface drop between pools and passable conditions over the boulders.

FULL WIDTH STREAM WEIRS - 
CAUTIONS

! It is especially difficult to maintain the required water surface elevation differential between the lowest weir and tailwater, when the design must encompass a wide flow range.

!!Additional instream work may be required to avoid impacts

to fish passage.

FULL WIDTH STREAM WEIRS - CAUTIONS

! If sills and weirs are not anchored on bedrock, a means of preventing undermining is required, using embedded anchor boulders or other such means of stabilizing the streambed. !

! In addition, the tailrace area should be protected from scour to prevent lowering of the streambed, and should be monitored after high flows occur to ensure the facility remains passable.

FISH PASSAGE ENGINEERS - 
THE END