The Environment Agency Eel Screening Guide

Transcription

1 The Environment Agency Eel Screening Guide 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 International Fish Screening Techniques Conference 2011 Tuesday 29th & Wednesday 30th March 2011 The Lyndhurst Park Hotel, Lyndhurst, Southampton

2 Why do we need a manual / guide? EC Regulation 1100/2007 Ensure safe passage Increase habitat Stocking Monitoring EMPs The Eel SI (Part 4) THE EEL MANUAL

3 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

4 Physical (Positive-Exclusion) Screens for Eels Bars may be vertical or horizontal Bars should be rectangular not round section Screen 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 )

5 Burst and sustained speeds of eel in relation to size (>15 o C) Size Sustained speed (cms -1 ) Burst Speed (cms -1 ) 10 cm cm cm cm

6 Advisory screen approach velocities for eel. Life stage Screen angle Φ 21 to 90 Elver/glass eel 10 cms -1 Screen angle Φ cms -1 (screen length <10 m) Yellow >14cm 15 cms cms -1 >30cm/silver eel 20 cms cms -1 Silver eel 40 cms cms -1

7 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 wedgewire 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).

8 Passive mesh panel screens

9 Bar rack Screens 1. 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)

10 Spillway Screens Aquashear Coanda screen, with a detail of the V-profile of the wedge-wire (Dulas).

11 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.

12 Physical screening for elvers and glass eels Where required, passive wedge-wire panel or cylinder screens or Hydrolox polymer screens can be used Mesh size 2 mm or less Escape velocity < 10cm/s

13 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)

14 Wedge-wire panel screens

15 Self-cleaning belt screens 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. Conceptual site layout with travelling screens (courtesy of Hydrolox).

16 Physical screens - Mesh size/bar spacing for exclusion (mm) - summary Life Stage Screen angle Φ >20 deg Screen angle Φ <20 deg Glass eel / elver Yellow eel (14 cm) Yellow / Silver eel (30cm) Silver eel (50 cm) 15 20

17 Non-Physical screens louvre 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

18 Non-Physical Screens Acoustic Fish Deterrents AFDs at normal frequencies ( Hz) ineffective for eel Infrasound (~10Hz) shows promise for eel but transducers are highly unreliable AFDs are suitable for a wide range of freshwater spp. Strobe Lights High Intensity Flashing Lights (strobes) are best behavioural technique for eel Flash rates have been shown to work Lower flash rates (66-240) avoid safety issues

19 Screening for Flood & Drainage Pumping stations Cul-de-sac: difficult to fit bywash Many species of coarse fish, including eels, overwinter in pump chambers Fish-kills can occur when pumps turned on

20 Fish Friendly Pumps - Archimedes screw pump Fish Flow Innovations Archimedes screw pump fish-friendly Landy Archimedes screw pump

21 Fish Friendly Pumps - Other Options Hidrostal pumps Fish-friendly impeller for an axial flow pump

22 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.

23 Alternative Routes Tauw Fish Flow system Fishway for pumping stations

24 Bywash Need to open to bed level Backfill Preferably full depth to handle a wide range of species 0.5m Backfill >1.0 x U 8.0 m (A) Plan Walls formed of timber faggots to ~2m allow modification if needed Channel velocity, U 8.0 m For steep angles 20 deg, bywash flow 2% of channel; for >20deg,at least 5% ~1m Ramped floor Key: 1.4 x U Bywash entrance box formed of concrete (B) Section Backfill ~2m U Water

25 Other options Trap and transfer Partial shut down 21:00 22:00 Time of Day of Migration for Silver Eels (October to December 2004 data) 23:00 00: :00 02:00 03:00 20: :00 19: :00 18: :00 17:00 07:00 16:00 08:00 15:00 09:00 14:00 13:00 12:00 11:00 10:00

26 How can I get a copy? Website: publications catalogue Mailing lists Internal: e mail to National Eel Group, key contacts External: press releases & letters