GUIDE TO THE APPLICATION OF THE REGULATION RESPECTING THE SUSTAINABLE DEVELOPMENT OF FORESTS IN THE DOMAIN OF THE STATE

Complete guide

Chapter V – Roads, sandpits and forest infrastructures
Division III – Bridge, culverts, removable structures and rudimentary structures
§3. Drying of work area

Section 93

Every person who installs coffer dams and structures for the temporary diversion of a watercourse, such as a diversion canal, to dry all or part of the work area during the construction, improvement, repair or removal of a bridge or a culvert must, in situations other than those described in section 103, ensure that the coffer dams and diversion structures do not prevent the flow of fish during more than 5 days and that they limit the carrying of sediments into the watercourse.  Where the period exceeds 5 days, the coffer dams and diversion structures must not reduce the width of the watercourse by more than 1/3. The width of the watercourse is measured at the level of the upper limit of the banks.

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Objectives

  • To limit the time during which the flow of fish is obstructed
  • To avoid carrying sediment into an aquatic, wetland or riparian environment
  • To preserve the integrity of an aquatic, wetland or riparian environment

Explanations

Coffer dams and structures for the temporary diversion of a watercourse, such as a diversion canal, are sometimes installed to dry all or part of the work area during the construction, improvement, repair or removal of a bridge or culvert. In a watercourse in which the free flow of fish must not be obstructed, these dams and structures must not prevent the fish from passing through for more than five days, and must also limit the carrying of sediments into the watercourse. Section 103 provides information on the watercourses in which the free flow of fish must not be obstructed.

Additional information

A coffer dam is a temporary dam (sometimes an embankment or enclosure) installed in the bed of a watercourse to dry it out so that work can be performed.

A diversion canal is a temporary canal built outside the bed of a watercourse to divert the flow so that work can be performed.

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Objectives

  • To ensure the free flow of water
  • To ensure the free flow of fish
  • To avoid scouring of the watercourse

Explanations

It may be that coffer dams and structures for the temporary diversion of a watercourse remain in place for several weeks, for example during construction of a bridge. Where a dam or structure is in place for more than five days, it must not reduce the width of the watercourse by more than one-third, to avoid causing the water to flow at speeds in excess of the swimming ability of the fish, and to avoid causing erosion in the remaining portion of the watercourse. The width of a watercourse is measured at the level of the upper limit of the banks.

Additional information

How is the width of a watercourse measured?

The width of a watercourse is calculated using the average of at least four representative measurements of the natural watercourse taken upstream and downstream of the crossing site. If there are signs of narrowing or widening, the section in question (e.g. area disturbed by a beaver dam) must be excluded. The width is measured at the level of the upper limit of the banks. The method used to identify the upper limit is shown in the definition of “bank”.

At the end of the work, the coffer dams must be removed and the diversion canal used during the diversion of the watercourse must be filled by restoring the vegetal cover.

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Objectives

  • To promote the reconstitution of the forest canopy
  • To avoid carrying sediment into an aquatic, wetland or riparian environment
  • To preserve the integrity of an aquatic, wetland or riparian environment

Additional information

The bed, banks and riparian zone of the watercourse must be stabilized as specified in section 114 of this Regulation.