Curved-Bar Rack Bypass Systems for

Downstream Fish Passage

FIThydro final Conference

Dr. Claudia Beck

18.03.2021

26.03.2021

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Mechanical behavioural fish guidance structures

Ur

VpVn

High hydraulic head losses

Asymmetric downstream flow field

HPP operators are hesitant to apply this technology

β = 45° – 90°

α = 10° – 45°

sb = 25 – 100 mm

β

α

sb

Vp > Vn

3

ξR = 14* ~ξR/5 = 2.6* ~ξR/20 = 0.6

Reduction of head loss coefficient:

Example:

• Rack angle α = 30°

• Clear bar spacing sb = 50 mm:

Most CH trash racks: 0.11 < xR < 3.0

(Meusburger 2002)

* Values from Kriewitz (2015)

Louver MBR CBR

Hydraulic head losses

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α = 30°, β = 45°, sb = 50 mm

2D CFD simulation averaged over 10 s Adapted from Leuch (2019)

α

α

β

β

sb

sb

Effect of bar shape on the flow field

5

Ethohydraulic testsMain objectives:

• Evaluate fish protection and guidance efficiency of CBR-BS

• Link fish behaviour to hydrodynamic cues

Tested fish species:

spirlin, barbel, nase, European eel, brown trout, salmon parr

Main tested hydraulic conditions:

• Mean approach flow velocities Uo = 0.5 m/s, 0.7 m/s

• Bypass entrance velocity ratio Uby,in/Uo = 1.2, 1.4

a = 30°, b = 45°, sb = 50 mm

0.25 m

CBR bypass

fish holding tank

submerged

cameras

Uo

Uby,in

starting

compartment

6

Fish Guidance Efficiency (FGE)

FGE > 85% for spirlin, barbel, nase & salmon parr

FGE < 60% for eels and brown trout

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Effect of flow conditions

→ Higher guidance efficiency for higher approach flow velocitiy (Uo = 0.7 m/s)

→ Higher guidance efficiency for lower bypass inflow velocity ratio (Uby,in /Ua = 1.2)

Uby,in /Uo ↑ ↓ ↑

↑

bypass

passage

rack

passagerefusal

Uo ↑ →

→

↑

3 binary logistic regression models for the response variables

I) bypass passage

II) rack passage

III) refusal

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Flow fields at the CBR-BS3D CFD simulation averaged over 20 s extracted at 125 mm over the flume bed

Pressure gradient

[Pa/cm]velocity gradient

[m/(sm)]

9

Fish: Nase

TL: 7.5 cm

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Summary & outlook

• Novel curved bar shape greatly improves the hydraulic performance

o Flow straightening effect symmetric turbine admission

o 4.2 times lower head losses compared to straight bar shapes

• Live-fish tests proved the behavioural barrier effect of

this fish guidance structure type

• CBR-BS have a large potential to protect and guide fish at HPPs and

water intakes with minimal impact on operation & production

• Numerical model allows for optimization of bar shape

and CBR-BS geometry

(Source: Fäh, Wälli AG, VAW; Patent pending EP21155988.5)

Thank you

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This project has received funding from the European Union's Horizon

2020 research and innovation programme under grant agreement No.

727830, FITHydro.