The Environment Agency Eel Screening Guide

International Fish Screening Techniques Conference 2011Tuesday 29th & Wednesday 30th March 2011

The Lyndhurst Park Hotel, Lyndhurst, Southampton

Steve Sheridan, Dave Bamford, Ben Bayliss, Steve Coates, Ian Dolben, Paul Frear, Emma Hazard, Ida Tavner, Neil Trudgill, Ros

Wright,

Andy

Turnpenny, David Solomon, Miran Aprahamian

Why do we need a manual / guide?EC Regulation 1100/2007

EMPs

The Eel SI(Part 4)

THE EEL MANUAL

Ensure safe passage

Increase habitat

Stocking

Monitoring

Eel Behaviour at Screens

The problem -

eel tend to force themselves through screens gaps smaller than their body diameter if there is no easy escape route

Physical (Positive-Exclusion) Screens for Eels

Bars may be vertical or horizontalBars should be rectangular not round sectionScreen should be set flush with riverbank or diagonally across channel (preferably Φ

≤20 degrees to the channel axis)

Screen angle to flow,

Φ,Approach velocity (Ue) Axial channel velocity (Ua)Sweeping velocity (Us

)

Burst and sustained speeds of eel in relation to size (>15 oC)

Size Sustained speed(cms-1)

Burst Speed(cms-1)

10

cm 18 107

30 cm 27 115

50 cm 47 125

70 cm 66 132

Advisory screen approach velocities for eel.

Life stageScreen angle Φ 21 to 90°

Screen angle Φ ≤ 20°

Elver/glass eel 10 cms-1

25 cms-1

(screen length <10 m)

Yellow >14cm 15 cms-1 30 cms-1

Silver eel 40 cms-1 50 cms-1

>30cm/silver eel 20 cms-1 40 cms-1

Physical screens -

Yellow & Silver eel

traditional passive mesh screens –

these screens are commonly used to exclude fish, but usually require manual cleaning; self-cleaning vertical or horizontal bar screens; self-cleaning Coanda

screens –

these wedge-

wire spillway screens are mainly used with upland hydropower schemes; the ‘Smolt-Safe™’

screen –

another type of

spillway screen; band-

or drum-screens that have been modified

for fish recovery and return (FRR).

Passive mesh panel screens

Bar rack Screens1.

Screens inclined by 10 degrees to the vertical -

makes raking

easier;2.

Bars need to be sufficiently stiff to maintain the design spacing throughout the screen –

this

may require horizontal tie-bars to be fixed across the back of the screen;

3.

Eel > 30 cm -

bar spacing 9 - 20 mm (depending on angle

and adult life stage)

Spillway Screens

Aquashear™ Coandascreen, with a detail of the V-profile of the wedge-wire (Dulas).

Physical screens -

Glass eel/ Elver

passive wedge wire cylinder (PWWC) screens –

this is the most widely used

method for juvenile and larval fish protection; small-aperture, wedge-wire panel screens; sub-gravel intakes and wells –

these use the

riverbed as a filter; self-cleaning belt screens such as Hydrolox™.

Physical screening for elvers

and glass eels

Where required, passive wedge-wire panel or cylinder screens or Hydrolox

polymer screens can be usedMesh size 2 mm or lessEscape velocity < 10cm/s

Passive wedge-wire cylinder (PWWC)

2 mm spacing would stop elvers

>1 g (~10.7 cm in

length); slot-width of 1 mm would be required to stop the earliest (0.2 g) glass eels;3 mm spacing would stop anything larger than 3 g (~14.5 cm).

Knights (1982)

Wedge-wire panel screens

Self-cleaning belt screens

Conceptual site layout with travelling screens (courtesy of Hydrolox).

1.

the large filtration area with low approach velocities, typically designed at 0.15 ms-1;

2.

the sealed edges and smooth mesh surfaces minimises fish injury and impingement;

3.

the non-adhering surface discourages the build up of debris.

Physical screens -

Mesh size/bar spacing for exclusion (mm) -

summary

Life Stage Screen angleΦ

>20 deg

Screen angleΦ

<20 deg

Glass eel / elver 1-2 1-2 Yellow eel (14 cm)

3 3Yellow / Silver eel(30cm)

9 12.5

Silver eel (50 cm) 15 20

Non-Physical screenslouvre

screens

–

this semi-physical barrier may have some

potential for silver eels; bubble curtains

–

this most basic behavioural barrier provides

relatively poor protection but is sometimes useful as a temporary measure; electrical barriers, such as the ‘Graduated Field Fish Barrier (GFFB™)’, are suitable for outfalls (provided that they contain no descending fish) but not for intakes; acoustic fish deterrents

–

as yet there are no forms suitable for

eel; artificial lighting

–

such as strobe lights –

either illuminate

physical structures or act as an attractive or repellent stimulus

Non-Physical Screens

AFDs

at ‘normal’ frequencies (20-1000Hz)

ineffective for eel Infrasound (~10Hz) shows promise for eel but transducers are highly unreliableAFDs

are suitable for a

wide range of freshwater spp.

High Intensity Flashing Lights (strobes) are best behavioural technique for eelFlash rates 66-1100 have been shown to workLower flash rates (66-

240) avoid safety issues

Acoustic Fish Deterrents Strobe Lights

Screening for Flood & Drainage Pumping stations

Cul-de-sac: difficult to fit bywashMany species of coarse fish, including eels, overwinter in pump chambersFish-kills can occur when pumps turned on

Fish Friendly Pumps -

Archimedes screw pump

Fish Flow Innovations Archimedes screw pump

“fish-friendly”

Landy

Archimedes screw pump

Fish Friendly Pumps -

Other Options

Hidrostal

pumps

“Fish-friendly”

impeller for an axial flow pump

Alternative Routes

Location and accessibility of alternative gravity outfalls, and how often, how long and under what conditions do they operate;Can passage through the pumps be prevented or discouraged.

Alternative Routes

Tauw

“Fish Flow”

system

Fishway

for pumping stations

Bywash

Channelvelocity,

U

U

>1.0 x U

1.4 x U

(A) Plan

(B) Section

Walls formed of timber faggots toallow modification if needed

Backfill

Backfill

~2m

~2m

~1m

0.5m

Key:Bywash entrancebox formed of concrete

Backfill Water

8.0 m

8.0 m

Ramped floor

•Need to open to bed level

•Preferably full depth to handle a wide range of species

•For steep angles ≤20 deg, bywash

flow ≥2% of

channel; for >20deg,at least

5%

Other options

Trap and transferPartial shut down

Time of Day of Migration for Silver Eels(October to December 2004 data)

0

5

10

15

2000:00

01:00

02:00

03:00

04:00

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06:00

07:00

08:00

09:00

10:00

11:0012:00

13:00

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23:00

How can I get a copy ?

Website: publications catalogue

Mailing listsInternal: e mail to National Eel Group, key contactsExternal: press releases & letters