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Risk Assessmentand  

Monitoring and Evaluation

Consideration of Design and Construction of Culverts for Fish Passage: A Risk Assessment Approach

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As previously mentioned, TRANS’ risk is assessed in relation to activities regarding linear development e.g. culverts, bridges and highways. Therefore a risk assessment approach is being taken for fish passage.

Note: A separate risk assessment is being developed for habitat impacts.

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In nearly all cases TRANS’ design parameters do not

require mitigate or offsetting approaches since TRANS

culverts are designed to pass fish. Only specific cases (e.g. steeper than average slopes

etc.) are additional mitigative/offset measures

required.

Table 1.What can be addressed by applying the correct culvert design criteria for streams <1% slope

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Possible barriers to fish passage Design criteria to avoid any barriers Notes

Water depth

 • Design using the fish passage design discharge (FPDD)• Use the correct diameter of culvert for the flow that the crossing is being 

designed for• Do not oversize the culvert (bigger is not better)• Embed culvert (at ¼ diameter up to 1 meter) 

 • Events such as flood/droughts are not the reason that culverts don’t work; we 

design to the hydrotechnical parameters that are present in the ‘natural’ stream.

• See Section on oversizing culverts.• Embedment results in increased area and decreased velocity• Tailwater control structures can add increased water depths in the culvert 

through the backwater effect

Water velocity

• Design culverts to match stream velocities that are present in the stream• Add ‘roughness’ to create lower velocities especially along the margins• Be aware that in normal situations and under normal flows substrate will move 

in and out of a culvert based on flow; substrate holders are utilized on streams >1% slope to add roughness

• Match culvert slope 

• Recognize that a culvert’s velocity is an ‘average’ velocity;  velocities are varied throughout   a culvert especially near the    outer margins• Fish tend to be energetically efficient and will seek out lower velocity zones if 

needed • Tailwater control structures reduce velocity at the culvert outlet and provide a 

transition zone between the culvert and the natural stream bed

Culvert Length (Swim distance) • Variable amongst species; could possibly be an issue in rare circumstances  • Fish will move to meet life requirements. Certain species can meet their life requirements in small area (small pond); others travel many kilometers to meet life cycle requirements. More research is required for many species.

Perching (invert at outlet raised above streambed)

• Embed culvert• Use adequate erosion control especially near the outlet of the culvert

 

Changing sediment concentrations • Apply adequate erosion and sediment protection during and after the project is complete.

 

Light Conditions (e.g. darkened corridor) N/A Fish (depend on species) have evolved to see through various water conditions and have other sensory organs to guide them. Light conditions are not considered a hindrance to fish passage at this point. See Appendix #.

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Table 1. (First criteria)

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Possible barriers to fish passage

Design criteria to avoid any barriers

Notes Y/N

 Water depth

• Design using the fish passage design discharge (FPDD)

• Use the correct diameter of culvert for the flow that the crossing is being designed for

• Do not oversize the culvert (bigger is not better)

• Embed culvert (at ¼ diameter up to 1 meter)

• Events such as flood/droughts are not the reason that culverts don’t work; we design to the hydrotechnical parameters that are present in the ‘natural’ stream.

• See Section on oversizing culverts.

• Embedment results in increased area and decreased velocity

• Tailwater control structures can add increased water depths in the culvert through the backwater effect

Table 1 – expandedColumn 1

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Possible barriers to fish passage

Water depth

Column 2 Design criteria to avoid any barriers

• Design using the fish passage design discharge (FPDD)

• Use the correct diameter of culvert for the flow that the crossing is being designed for

• Do not oversize the culvert (bigger is not better)

• Embed culvert (at ¼ diameter up to 1 meter)

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Column 3

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NotesN

• Events such as flood/droughts are not the reason that culverts don’t work; we design to the hydrotechnical parameters that are present in the ‘natural’ stream.

• See Section on oversizing culverts.• Embedment results in increased area and decreased velocity

• Tailwater control structures can add increased water depths in the culvert through the backwater effect

If these and other conditions are met (velocity criteria, slope etc.) then the culvert may be installed without referral to DFO.

Remember, all conditions to protect the environment must be followed.

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Monitoring(Performance Evaluation)

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At this point there has been some monitoring completed at certain culvert sites. However, this has not been a standard approach and some of the information is anecdotal.

We do know that:

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• Fish consistently out perform previous expectations based on laboratory studies

• Fish have senses adapted to aquatic environment

• Dependent on species and motivation, fish move through a variety of flow conditions

• Fish will move through culverts

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Standards:

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TRANS will be completing two ‘intensities’ of monitoring regarding fish passage.

For fairly similar projects (e.g. Northern Pike in the Red Deer fisheries management area) monitoring studies on a representative number (~10 to 15%) of culverts would be fairly simple.

‘Simple’ usually involves tagging or marking fish in such a manner to see if these fish move through the culverts.

Visible Implant Elastomer (VIE)

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More intensive types of monitoring will occur only at specific sites (~ 5%). It will include monitoring parameters such as velocities, flows, and other data to obtain a more detailed ‘picture’ of the interacting dynamics.

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Interpreting and explaining the similarities between culvert design and fish passage principles is required for an integrated approach that will result in culvert structures that are both cost effective and consistent with fisheries management objectives.

Forthcoming to address fish passage:• Standards and guidelines for fish

and fish habitat assessments• Risk assessment framework• Guidelines for fish passage

design• Guidelines for when to apply to

DFO• Guidelines for regulatory

applications20

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The End