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Fish Passage Remediation Example

Hi everyone,

Check out the video below showing a great example of fish passage remediation targeting small-bodied NZ fish species.

The fixes address:

  • The perched apron
  • The perched culvert outlet
  • Shallowing of the apron
  • Fast laminar flow within the culvert

Note: This culvert should have been embedded to both retain bed material and allow good fish passage.

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Fish Passage Guidelines

Hi everyone

The Fish Passage Action Team have been working on a simple one-page guide to help with the remediation of common structures causing a barrier to fish.

The guide includes a link to an interactive decision tool and some helpful before & after examples.

Happy holidays!
 

Fish Passage Remediation (existing structures)

Overview

Fish passage remediation is less about target species, specific swimming speeds, average velocities, Mannings numbers etc., and more about understanding the medium in which fish have evolved to navigate, i.e. water, with the dynamics of complex flows and boundary layers all at a fine resolution.

Basic principles – “Match or better” the streamflow characteristics.

– Provide complex flows (non-laminar) – multi-directional flows with rest pools.
– Length of fast flow zones between rest pools must be shorter than fish burst-swim capabilities.
– Provide sufficient depth.
– Ensure continuity – no overhangs.
– Give fish a range of navigation path options.
– Ideally, retain bed material.

General rules.

– Rope should not be used in culverts if baffles can be fitted, even if climbing species are targeted.
– Ramps should include splash zones and substrate, e.g. rope.
– Ramps should extend into the plunge pool as far as practicable.
– Baffles should be spaced so that the rest pool from one extends easily up to the next.
– Baffles may be considered artificial bed material in some situations, i.e. create similar hydrological conditions
– If rope is fitted through a culvert that is also perched, a second set of rope should be fitted at the outlet.
– Rope should only be attached at the upstream end.
– Interventions should not significantly reduce culvert capacity or increase the risk of debris jams.
– Tide-gates should be designed/modified to delay the closing as long as possible.
Which tools to use where?

The above principles help to guide us towards selecting appropriate remediation tools.
For more detailed guidance on the use of remediation tools click here: 

Remediation Decision-Tree Interactive Tool

Before & after examples click here:https://www.ats-environmental.com/before-after-remediation/

Measures of success:
Success should be outcome-focused and easy to measure or observe.
– Complex flows similar to stream (depth, width, velocities)
– Bed material retained.
– Continuity – no perch or overhang.
– Extended opening period for tide gates.

Please note that the linked resources above are kindly provided by ATS Environmental.
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Mussel-Rope Heads-Up

Many of you will be familiar with the use of mussel-rope to help improve fish passage over or through structures including culverts.

The rope helps to reduce the water velocity adjacent to the rope and also gives a tactile surface for small fish to wriggle through or over.

Rope is a good tool when there is no other option, however it does not create resting pools, add depth, or retain bed-material.

While we have installed many 1000’s of meters of mussel-rope, it is important to understand that there are limitations as to where mussel-rope can be used and where it is not suitable.

Mussel ropes can be used to enhance fish passage on existing structures where: –

  • Culverts are perched and fitting ramps is not practical.
  • It is not practical to install baffles e.g. culvert diameters <800mm

Other notes:

  1. Based on our extensive experience, it is best not to attach the downstream end of the rope as this has been known to cause blockages when logs, debris etc gets caught under the rope.
  2. Fixings should be roust e.g. stainless steel D-ring and clasp – NOT a waratah.
  3. “Swimming lanes” are rarely achievable when installing ropes through smaller diameter pipes because these pipes typically have very low flow. It is even more challenging if the pipe is also long.
  4. There is no evidence that “swimming lanes” are more effective than a number of ropes laying close beside each other.
  5. When aiming to get fish up a perched or overhanging structure, it is best to first attach a strip of rubber in order to create a wetted margin.                                    See Tim’s video link below.
  6. Looped-rope is less likely to shed fibers than Super-Christmas-tree rope and there is no evidence of it being more likely to cause a blockage.
  7. The cut ends of the ropes should be melted to prevent fraying.
  8. If rope is used through a culver that is also overhanging, there should be twos sets – one set attached at the upstream end and finishing at the outlet, with a second set attached at the outlet hanging down into the plunge-pool.

In summary:

Mussel-ropes should only be used as a last resort when remediating existingstructures where ramps, baffles etc are not practical.

We are always willing to listen, help. share and learn, so please feel free to contact us however and whenever..

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Eels

This short video shows elvers climbing across both smooth and rough surfaces. 

The urge to overcome obstacles is powerful and you can see individuals climbing over each other.

The more we watch these creatures, the better we understand their capabilities and limitations when we are considering remediation.

Click here or on the image below
https://www.youtube.com/watch?v=FEQVQIl7dpc

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Focus On Maintaining Fish Passage During Low Flows

It is worth remembering that lows flows and shallow water are challenges to migrating fish. 
The video below represents remediation to an upgraded urban storm water pipe serving a small tributary of the Maitai River near Nelson, NZ.

The upgrade involved upsizing the pipe and removing the perch at the outlet.

– Base flows of the tributary are approximately 1L/S
– Pipe length 300M
– Pipe gradients range from 2%-12%

You will see an increase in the depth and width of the water along with bed-material beginning to accumulate.

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GIS Project

Jordie McDonald has completed a desktop GIS project highlighting the huge number of potential barriers to fish passage in the Northland Region of New Zealand.

The extent of the potential barriers is probably typical around NZ the rest of the world.

https://northtec.maps.arcgis.com/apps/MapJournal/index.html?appid=4342b312ac164e0aa83c9793936fa0b1

We will soon share a report on a large catchment where each site is visited and assessed. A “current status” is assigned to each in order to give a better picture of what is out there and what needs to be done to remediate. Enjoy!

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Lessons Learnt 8

The NZ Dept Conservation Fish Passage Advisory Group website has a number of Lessons Learnt describing different fish passage remediation projects.

Tim Olley spent over a year researching and putting together this comprehensive report highlighting the effectiveness of flexible baffles in a long, steep culvert.

We are planning to make a PowerPoint and/or video of this report at some point.

Enjoy.

Click here to view Lessons Learnt 8