the environment agency eel screening guide · the environment agency eel screening guide...
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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
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11:0012:00
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How can I get a copy ?
Website: publications catalogue
Mailing listsInternal: e mail to National Eel Group, key contactsExternal: press releases & letters