Interim code of practice: Temporary cofferdams and diversion channels

1.0 About this code of practice

This code of practice outlines national best practices for the installation of temporary cofferdams and diversion channels to isolate a section of a watercourse or water body in order to conduct works, undertakings and activities in the dry while maintaining the natural downstream flow and coastal currents. This document can be used in the planning, design and construction of in-water projects.

Effective worksite isolation can significantly reduce unnecessary damage to fish and fish habitat. Some potential impacts to fish and fish habitat from cofferdams and diversion channels include, but are not limited to, direct damage to substrates, the release of sediments, the loss of riparian habitat, the stranding of fish in dewatered areas and impingement/entrainment of fish at pump intakes.

In most cases, this code of practice will be referenced in requests for review of works, undertakings and activities that require site isolation. If other aspects of your project (other than the temporary cofferdam or diversion channel ) have the potential to cause impacts to fish and fish habitat that are not addressed by the measures to protect fish and fish habitat, request a project near water review.

This code does not remove nor replace the obligation to comply with all applicable statutory and regulatory requirements of the Fisheries Act, the Species at Risk Act or other federal, provincial, or municipal legislation and policy.

2.0 You can use this code of practice if:

• There are no aquatic species listed under the Species at Risk Act, or critical habitat or residences of endangered or threatened aquatic species present in the work zone or the vicinity of the works, undertakings and activities. Consult our aquatic species at risk maps to determine where at-risk populations occur in Canada and where their critical habitat is located
• If the riparian area is identified as part of the critical habitat of an aquatic listed species at risk, there must be no temporary or permanent increase in existing footprint above the ordinary high water mark (see definition below)
• The use of explosives is not required to complete the works, undertakings and activities
• Fish passage is maintained during the works, undertakings and activities
• You follow the measures in this code of practice and all other applicable measures to protect fish and fish habitat

3.0 Measures to protect fish and fish habitat

3.1 Protection of fish

• Plan in water works, undertakings and activities to respect timing windows to protect fish and fish habitat
• Limit the duration of in-water works, undertakings and activities so that it does not diminish the ability of fish to carry out one or more of their life processes (e.g., spawning, rearing, feeding, migrating)
• Screen intake pipes to prevent entrainment or impingement of fish
• Follow Interim code of practice: End of pipe fish protection screens for small water intakes in freshwater, when using pumps
• Capture and relocate any fish trapped within an isolated/enclosed work area and safely relocate them to an appropriate location in the same water body
• Dewater gradually to reduce the potential for stranding fish
• Relocate any fish as per applicable permits for capturing and relocating fish

3.2 Protection of fish passage

• Maintain fish passage during all phases of works, undertakings and activities
• Avoid changing flow or water levels
• Avoid obstructing and interfering with the movement and migration of fish

3.3 Protection of the riparian zone

• Use existing trails, roads, access points or cut lines wherever possible
• Avoid tree/shrub removal whenever possible
• Use methods to prevent soil compaction (e.g. swamp mats, pads)
• Do not grade streambanks or approaches
• Avoid stockpiling of material on stream banks and riparian zones
• Limit access to banks or areas adjacent to water bodies
• Prune or top the vegetation instead of grubbing/uprooting to ensure root structure stability
• Limit grubbing on watercourse banks to the area required for the footprint of the works, undertakings and activities
• Construct access points and approaches perpendicular to the watercourse or water body
• Remove vegetation or species selectively and in phases
• Re-vegetate the disturbed areas with native species suitable for the site
• Restore the banks affected by the work, undertakings and activities to their natural state (profile, vegetation, etc.)

3.4 Protection of aquatic habitat

• Avoid disturbing or removing aquatic vegetation, natural wood debris, rocks, sand or other materials from the banks, shoreline or the bed of the water body
• Operate machinery in a manner that minimizes disturbance to the watercourse bed and banks
• Salvage, reinstate or match habitat structure (e.g. large wood debris, boulders, instream aquatic vegetation/substrate) to its natural state

3.5 Protection of fish habitat from sedimentation

• Use only clean materials (e.g. rock, coarse gravel, wood, steel, snow) for works, undertakings and activities
• Develop and implement a sediment and erosion control plan to minimize sedimentation of the water body during all phases of the works, undertakings and activities
• Conduct all in-water works, undertakings and activities in isolation of open or flowing water to reduce the introduction of sediment into the watercourse
• Maintain the natural flow regime for any diversion works
• Schedule work to avoid wet, windy and rainy periods and heed weather advisories
• Regularly inspect and maintain the sediment control measures and structures during all phases of the project
• Regularly monitor the watercourse for signs of sedimentation during all phases of the works, undertakings and activities and take corrective action when needed
• Use biodegradable erosion and sediment control materials whenever possible
• Keep the erosion and sediment control measures in place until all disturbed ground has been permanently stabilized
• Remove all sediment control materials once site has been stabilized
• Operate machinery on land, from barges or on ice
• Use methods to prevent substrate compaction (e.g. swamp mats, pads)
• Dispose of and stabilize all excavated material above the ordinary high water mark or top of bank of nearby water bodies and ensure sediment re-entry to the watercourse is prevented
• Use appropriate isolation materials and designs to minimize disturbance to the bed and banks of the watercourse or water body
• Protect pump discharge areas to prevent erosion and the release of suspended sediments downstream
• Pump any residual water from the isolated worksite into a designated treatment area (e.g. settling pond, behind filter fabric dam, vegetated areas, envirobags)
  • Remove accumulated sediments from the isolated area before removing the isolation barrier
  • Partially reflood the dewatered site in order to re-suspend remaining deposits and pump any residual sediment-laden water from the site

3.6 Protection of fish and fish habitat from deleterious substances (including suspended sediment)

• Develop and immediately implement a response plan to prevent deleterious substances from entering a water body
  • Stop works, undertakings and activities in the event of a spill of a deleterious substance
  • Immediately report any spills (e.g. sewage, oil, fuel or other deleterious material), whether near or directly into a water body
  • Keep an emergency spill kit on site during the works, undertakings and activities
  • Contain any water with deleterious substances
  • Ensure clean-up measures are suitably applied so as not to result in further alteration of the bed and/or banks of the watercourse
  • Clean-up and appropriately dispose of the sediment-laden water and water contaminated with deleterious substances
  • Maintain all machinery on site in a clean condition and free of fluid leaks
  • Wash, refuel and service machinery and store fuel and other materials for the machinery in such a way as to prevent any deleterious substances from entering the water
  • Dispose of all waste materials (e.g. construction, demolition, commercial logging) above the ordinary high water mark to prevent entry into the water body
  • Plan activities near water such that materials such as paint, primers, blasting abrasives, rust solvents, degreasers, grout, poured concrete or other chemicals do not enter the watercourse

3.7 Additional measures for cofferdams

• Construct the cofferdam using non-earthen material (e.g. water-inflated portable dams, pea gravel bags, concrete blocks, steel or wood wall, clean rock, sheet pile or other appropriate designs)
  • Take the necessary measures to seal the cofferdams and thus minimize the amount of water to be managed
  • Use clean rock void of erodible material
  • Use adequately sized material (i.e. moderately sized rock and not sand or gravel) to withstand anticipated flows during construction
  • Construct cofferdams sufficiently high to prevent overtopping in the event of sudden increases in water levels
• Regularly inspect and maintain cofferdam during all phases of the project
• Do not excavate inside the cofferdam or sediment filtering curtain until the cofferdam/curtain/work area is completely isolated from flow
• Only install and operate dewatering pumps once the cofferdam is complete and isolation has been achieved
• Pumps should be monitored at all times, and back-up pumps should be readily available on-site in case of pump failure or high flow events

3.8 Additional measures for diversion channels

• Design the diversion channel to accommodate the peak seasonal flows for the time period the diversion will be in place
  • Ensure that the diversion channel is no longer than necessary
  • Stabilize and line temporary diversion channel with appropriate watertight material before any water flow is diverted from a natural channel into a diversion channel
  • Ensure slope of the diversion channel is similar to or lower in gradient than the natural watercourse
  • Use natural material to simulate natural stream conditions whenever possible
  • Install energy dissipation structures (i.e. rocks, sandbags) within the diversion channel
  • Align the downstream connection of the temporary diversion with the natural watercourse in a manner that avoids erosion on the opposite bank
• Regularly inspect and maintain the diversion channel during all phases of the project
• When connecting the diversion channel to the watercourse:
• Excavate the downstream end of the diversion channel towards the upstream point, where a 'plug' of earth should be left to prevent the entry of streamflow into the diversion before channelization
• Place a cofferdam immediately below the upstream point of the diversion to reroute the flow of water into the diversion
• Remove 'plug' once the channel is lined and lining secured
• Place another cofferdam immediately above the downstream point of the diversion channel to isolate the work area
• Proceed with the works, undertakings and activities once the area is effectively isolated from the stream
• When the diversion is no longer in use remove impermeable material, fill in, stabilize and revegetate the area of the temporary diversion channel to prevent erosion

3.9 Rewatering/reflooding the isolation area (partial or complete):

• Ensure that the watercourse is void of un-natural deposits of sediment within the footprint of the dewatered area
• Maintain sediment control measures during re-watering of the work site and removal of the cofferdam to ensure sediment is not released into the water body
• Remove the remainder of the cofferdam structure to allow the full return of flow to the permanent channel
• When returning flow (rewatering/reflooding):
• Ensure all components of the watercourse bed and banks within the footprint of the disturbed area and between the upstream and downstream water control structure(s) have been stabilized including any reinstated habitat features
• Ensure a maintenance flow is provided downstream to fish and fish habitat until the natural flow meets the water discharge location
• Gradually remove the downstream cofferdam first to ensure equalization of water levels inside and outside of the isolated area to allow suspended sediments to settle and to reshape the watercourse prior to the return of flow from the upstream reach
• Remove the upstream water control structure slowly as to allow for a partial return of water to the dewatered channel
• Once the banks are stabilized and the diversion channel is filled in, the diversion channel cofferdams can be removed

4.0 Project notification

This code of practice is intended to be referenced in a request for review of works, undertakings and activities that require site isolation. When making use of this code of practice, please submit a Notification Form (PDF, 50 KB) to your regional DFO office to help us improve this fish and fish habitat protection guidance over time.

It is your Duty to Notify DFO if you have caused, or are about to cause, the unauthorized death of fish by means other than fishing and/or the harmful alteration, disruption or destruction of fish habitat. Such notifications should be directed to the Fish an Fish Habitat Protection Program.

5.0 Contact us

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

6.0 Glossary

Cofferdam

A temporary structure used to isolate and dry out an area in a watercourse or water body to allow work to be carried out in the dry while maintaining downstream flow and coastal currents.

Deleterious substance

Any substance that, if added to any water, would degrade or alter or form part of a process of degradation or alteration of the quality of that water so that it is rendered or is likely to be rendered deleterious to fish or fish habitat or to the human use of fish that frequent that water.

Diversion channels

A temporary structure used to divert water form a watercourse to conduct instream work in the dry while maintaining downstream flow.

Entrainment

Occurs when a fish is drawn into a water intake and cannot escape.

Impingement

Occurs when a entrapped fish is held in contact with the intake screen and is unable to free itself.

Ordinary high water mark

The usual or average level to which a body of water rises at its highest point and remains for sufficient time so as to change the characteristics of the land. In flowing waters (rivers, streams) this refers to the “active channel/bank-full level” which is often the 1:2 year flood flow return level. In inland lakes, wetlands or marine environments it refers to those parts of the water body bed and banks that are frequently flooded by water so as to leave a mark on the land and where the natural vegetation changes from predominately aquatic vegetation to terrestrial vegetation (excepting water tolerant species). For reservoirs this refers to normal high operating levels (Full Supply Level).

Riparian zone

Area adjacent to streams, lakes, and wetlands that support a unique mixture of water tolerant vegetation from trees and shrubs to aquatic and herbaceous plants.