Interim code of practice: End-of-pipe fish protection screens for small water intakes in freshwater

1 About this code of practice

This code of practice provides national guidance on the design, installation and maintenance of small end-of-pipe water intake fish screens to prevent entrainment and impingement of fish. Entrainment occurs when a fish is drawn into a water intake and cannot escape. Impingement occurs when a fish is held in contact with the intake screen and is unable to free itself.

The end-of-pipe fish screen code of practice describes best practices to follow when designing, installing, maintaining and cleaning low volume water intakes that have the potential to impact fish. This code of practice is for small-scale water intakes (e.g. irrigation, construction, municipal and private water supplies, mining exploration) where the water intake flow rate is up to 0.150 m3/s, or 150 litres per second (L/s). Impacts related to fish habitat and changes in flow conditions are not covered by this code of practice.

When working in water, it is important to have a good understanding of local conditions. For example, water velocity, flow, depth, the type of fish species present and their abundance and swimming abilities are all important factors to consider when designing, installing, maintaining and cleaning small end-of-pipe water intake fish screens. This code of practice provides necessary information and guidance on the measures to follow to ensure maximum protection of fish. The sizing and design specifications of fixed screens in this code are exclusively for fish that have a minimum fork length of 25 mm. Entrainment and impingement impacts on eggs and larval fish can be minimized by following the measures below.

A project review is not required when the conditions and measures set out in this code of practice and all applicable measures to protect fish and fish habitat are applied.

This code does not remove or replace the obligation to comply with all applicable statutory and regulatory requirements in place by other sections of the Fisheries Act, or other federal, provincial, or municipal legislation and policies associated with water extraction.

2 You can use this code of practice if:

Request a project near water review when the works, undertakings or activities do not meet all the criteria listed in this section.

3 Measures to protect fish and fish habitat for end-of-pipe fish screens

1 Fish screen design

Three criteria need to be considered when designing a fish screen for water intakes:

1.1 Effective screen area

Larger screens reduce the approach velocity so fish are more likely to outswim the flow entering the intake. The screen area needed depends on the amount of water being withdrawn and the species of fishes that frequent the intake location. The total submerged screen area available for the free flow of water is referred to as the effective screean area.

1.2 Screen material

For a fish screen to prevent entrainment, the openings must be small enough so a fish cannot pass through. The narrowest dimension of any opening on the screen, regardless of opening shape, is referred to as the design opening (Figure 1). The maximum design opening for a fish of 25 mm fork length is estimated at 2.54 mm.

Figure 1

Figure 1: Drawing showing the profile of the wedge wire screen with features pointed out: design opening, flow, long narrow slots, wedge wire, increasing opening size reduces clogging. The design opening should not exceed 2.54 millimetres.

Figure 2

Figure two. Drawing showing typical end-of-pipe screen designs including perforated plate (punched), circular mesh screen, square mesh screen, square edge wire screen, drum or cylinder with perforated pipe, and box-type with mesh screen.

1.3 Screen shape

Use a manifold on designs where the flow would be uneven across the surface of the screen (e.g.: cylindrical or box type) (Figure 3).

Figure 3

Figure three. Drawing showing the common screen area shapes and area formula. Includes sizing for circular screen, square screen, box screen, and cylindrical screen.

2 Fish screen installation

Consider the following best practices when installing a fish screen:

3 Screen maintenance and cleaning

Debris or damage to screens can cause uneven intake flow across the screen surface. Uneven flow may result in higher intake velocities on some sections of the screen, increasing the likelihood of impinged fish. You can verify the pump’s approach velocity to assess the need for screen cleaning using a flow meter. Keeping fish screens clean maintains their effectiveness for supplying water and protecting fish.

4 Project notification

Please submit a Notification Form to your regional DFO office to help us improve this fish and fish habitat protection guidance over time.

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5 Contact us

If you have questions regarding this Code of Practice contact the Fish and Fish Habitat Protection Program located in your region.

6 Glossary

Affected area
Area within which potential impacts from works, undertakings or activities are likely to occur.
Approach velocity
The water velocity measured directly in front of the intake screen.
Benthos
Organisms that live on or in the bottom sediments of a body of water.
Design opening
The narrowest dimension of any opening on the screen, regardless of opening shape.
Effective screen area
The area of the open spaces available for the free flow of water, including screen material but excluding major support structures.
Entrainment
Occurs when a fish is drawn into a water intake and cannot escape.
Fork length
The straight line distance measured from the tip of the nose to the fork of the tail of a fish.
Impingement
Occurs when an entrapped fish is held in contact with the intake screen and is unable to free itself.
Intake flow rate
The amount of water withdrawn over time.
Littoral zone
The shallow water near shore. The depth of the littoral zone varies but is generally 2-5 meters deep in most freshwater systems.