Fish Ladders & SHP - UK Experience British Hydropower Association Steve Cryer - Chairman
Fish Passes to enable the Upstream and Downstream Migration of Salmonids are enshrined in legislation • Salmon and Freshwater Fisheries Act England and Wales 1975 • Salmon (Fish Passes and Screens) Scotland Regulations 1994 • Fisheries Act Northern Ireland 1966
Fish Pass Issues • New development schemes • Existing schemes on rivers that have relatively small weirs • Existing schemes with larger weirs and dams circa >5m
Fish Pass Types • Pool and Step with variations • Borland Lift • or alternatively none at all - loss of spawning grounds above the SHP abstraction point being ameliorated by hatcheries supplementing fish stocks
Typical Pool and Step Design
Typical Pool and Step Design • Pools need to be large enough and deep enough to keep turbulence to a minimum • The height of the step is kept to circa <0.5m to encourage fish to move up • The sides need to be high enough to prevent fish from jumping out • The velocity of the water through the steps must be within the swimming speed of the target species of fish
Typical Pool and Step Design • • • • •
Denil design Diagonal Baulk Pool and steps being built of natural rock formations etc. Pool and weir with underwater orifice as shown below These tend to be the exception rather than the rule
Optimum Position of a Fish Pass â&#x20AC;˘ The Fish Pass is located close to the intake screen It is important to ensure the correct angle of the screen in relation to the river flow to reduce the velocity through the screen to less than the body length speed of the target species and attract them into the fish pass
Alternative Fish Pass Arrangement â&#x20AC;˘ With this design the fish are allowed to enter the Headrace and are returned to the river via a bywash, situated in front of the turbine screen â&#x20AC;˘ This arrangement is generally found at old mill sites
Borland Lift
Borland Lift Performance Assessment • Underwater cameras in the tailrace and exit chamber • Fish counters at the entrance and exit points • This provides information to optimise the operation of the lift i.e. flowrates, duration time of operation, number of operations and time of day for these operations • Ongoing studies.
Fish Pass Assessment Brief overview of a study undertaken on the River Tavy at Abbey Weir, Tavistock in South West England UK
River Tavy Low Flow Scenario
River Tavy Low Flow Scenario
River Tavy High Flow Scenario
Abbey Weir and Fish Pass
Fish Tracking at Abbey Weir
Sample of Tracking Results
Abbey Weir and Fish Pass • It can be seen from the results that fish behaviour is unpredictable - female fish? • The maximum time recorded from fish entering and leaving Station TV5, when it has ascended the weir, is 12hours • The minimum time is in minutes • Despite the design not conforming to the general standard the passage of fish is not unduly impaired
Abbey Weir and Fish Pass • The results to the study indicate that the fish pass at Abbey Weir does work, despite not conforming to an ideal design. • More work needs to be done to verify the data, tagging a greater number of fish and looking at a greater range of flow scenarios • But I do not expect the results to change that much
Abbey Weir and Fish Pass • We have learnt several lessons over this • It is important to carry out field as well as desk top studies when examining the performance of existing weirs • Discussions with local people and long term anglers. In this instance it revealed that the anglers do not fish the pools immediately downstream of the weir as there is little likelihood of a catch
Abbey Weir and Fish Pass • Historical research can reveal some interesting aspects • Here it was found that a step and pool pass did exist at this site in 1928 • It was modified to the current arrangement at the insistence of the owner of the river at the time “The Duke of Bedford” (who also had extensive fishing rights upstream and downstream of the weir) before granting permission for the hydro plant to be built • How this design came about we do not know but it is effective
Abbey Weir and Fish Pass There are two wise principles it is good to follow
• BATNEEC – Best Available Techniques Notwithstanding Excessive Economic Cost and a favourite with Engineers
• If its not broken don’t fix it
Finally a thought Studies of fish passes are expensive So --- who pays It is likely that the investment and revenue stream for SHP will not be able to fund this work. Should this cost be shared with the community that wishes to benefit from environmental improvement
THANKYOU