Noveldesign,installationandassessmentofcoarsefishpassageusingtheLowCostBaffle(LCB)solutionatagaugingstation

TobyHullSouthEastRiversTrustSeniorProjectOfficer

What did the fish say when it swam into a wall?

Pollocks

Gauging Weir??

The Problem

- Impassable barrier at most/all flow conditions (coarse fish)- Active Gauging Station

- Non-standard flume construction- Steep downward slope 1:3.3

- Flat 2.4m wide crest with shallow flows- Very Urban Location

Gauging Accuracy Fish Passage

ProjectBackground

Hogsmill River Connectivity Project

Aim : Catchment scale fish passage

Started in 2012 as a CRF Project

18 barriers identified in total

Tackling the last few now

The Problem

TheProblemLow Cost Baffle Solution (LCBs)

The ProblemLow Cost Baffle Solution (LCBs)

=

- Developed for use on 1:5 slope- 200mm high baffles- 400mm centre spacing- 250mm notch- 200mm off-set- Upper baffles 1m from crest(600mm with a 120mm baffle)

Source ‘Servais, 2006’

> 0.6 drowned-out factor/ratio

1 : 5 slope120mm / 200mmDrowned out ratio = 0.6Streaming FlowPassable

1 : 3.3 slope83mm / 200mmDrowned out ratio = c.0.4Plunging FlowImpassable

32

32o

42o

Increasing Baffle Heights&

Fix all other variablesSolution =

Gauging Accuracy Fish Passage

Positioning Top Baffle

Positioning Top Baffle

Theoretical with no modelling

Baffled by Science ???

Positioning Top Baffle

Positioning Top Baffle

ModelledNo change in gauging accuracy

Positioning Top Baffle

ModelledInaccuracies at flows > 6.38 cumecs

Positioning Top Baffle

Positioning Top Baffle

ModelledInaccuracies at flows > 6.38 cumecs

Positioning Top Baffle

ModelledReduction to 120mm baffle

Velocity ≈ 2m/sec

Delivery

Delivery

Hogsmill HyrdographInfluence from STW

Low Flows High Flows

Monitoring

Aims 1). Inform if passage has been achieved at the Kingston site

2). Provide insight as to whether the principle of the modified baffle design can be applied to other weirs

Monitoring

Monitoring

- No mains power at the site

- Fish passage video surveillance software very expensive

- Without software many hours of reviewing footage

- High likelihood of missing passage (speed, user error, high turbidity, poor image quality etc)

- At best would only demonstrate if baffles passable, not the whole weir

Monitoring

Monitoring

MonitoringPIT Tagging (Passive Integrated Transponder)

Monitoring

Monitoring

A1 A2 A3

Monitoring

Monitoring

Monitoring

Stocked Fish- Age 1+- Source: EA’s Calverton Fish Farm

Mean Range Mean RangeBarbel Stocked 120 191 168 – 210 79 53 – 109Chub Stocked 119 177 160 – 209 76 53 – 129Chub Wild 194 319 178 – 525 605 71 – 2,494Dace Wild 50 187 142 – 227 100 35 – 202Roach Wild 30 221 142 – 300 224 46 - 501

Species Source No. Length (mm) Mass (g)

513 fish in study

Results

Monitoring undertaken since 21st February 2017 (c.5 months)

Headline Stat62 tagged fish have successfully passed the weir

(12% of total tagged fish)

Results

Monitoring undertaken since 21st February 2017 (c.5 months)

Headline Stats

Baffles Weir

Stockedc.40% bafflesc.30% over weir

Wildc.50% bafflesc.40% over weir

Results

Results

Results

Results AnalysisPassage is being assessed in terms of:

- Temperature - Flow- Diurnal Patterns- Depths- Velocities

Results

Conclusion

1). Inform if passage has been achieved at the Kingston site

Project/Monitoring Aims

2). Provide insight as to whether the principle of the modified baffle design can be applied to other weirs

Passage with 35% efficiency across the entire structure has be achieved.

The downslope of the weir has 45% efficiency at the 1:3.3 slope. Thisdemonstrates that weirs with a slope shallower than this can be madepassable using this novel approach.

Can weirs with even steeper gradients be made passable by adopting the principle of increasing baffle heights.

??

Lessons Learnt• Fragility of maintaining apparatus and continuous data collection over

prolonged periods

Lessons Learnt

• Fragility of maintaining apparatus and continuous data collection over prolonged periods

• Taking a science based approach

• Collaborative working & good communication between stakeholders to find a satisfactory outcome for all

• Be experimental but best done with robust monitoring. Evidence like this can then be rolled out with confidence

What’s Next- Second electrofishing survey and tagging of fish upstream

and relocation downstream (testing homing instinct)

- JBA continue spot gauging program to assess the impact of the baffles on gauge accuracy and revise weir rating accordingly

- Angus Lothian (Durham Uni.) will undertake the analysis of the findings and draw conclusions as part of his PhD

- Disseminate findings for the ‘Greater Good’

Contributions

Angus Lothian , Dr Martin Lucas, Jeroen Tummers

Toby Hull & Dr Chris Gardner

Chris Di Marco, Darryl Clifton-Dey & Dan Griffiths

Thank you.

If you have any questions, please let minnow