1

Explanations

The outlets create a series of thresholds and basins in the culvert so that the water speed and depth are sufficient to ensure the free flow of fish.

All the conditions indicated in Schedule 10 must be complied with when installing a culvert with outlets. If it is not possible to comply with a given condition (e.g. if it is difficult to comply with burial conditions due to the presence of rock), another type of structure (arch, bridge, etc.) must be installed instead.

Additional information

The decision tree below can be used to decide on the type of structure that must be installed to cross a watercourse.

2

Additional information

The slope of a watercourse is measured between two natural thresholds unaffected by the work (excavation, conduit installation, riprap, etc.). A threshold is an elevation of substrate across a watercourse that is not necessarily perpendicular to its axis and that is situated between the two deepest sections.

In a watercourse with a standard profile (no thresholds, channels or rapids), the slope may be measured from arbitrary points on the watercourse thalweg.

The slope of a watercourse must be assessed using a device that is sufficiently accurate. For example, a preliminary estimate may be made using a clinometer, but more accurate instruments, such as a precision sight level or an integrated set of measuring instruments that automatically measure both angles and distances during a land survey, are needed at the culvert installation stage.

The preliminary estimate of the slope of the watercourse when marking the course could help guide the initial selection of the type of structure suitable for the watercourse to be crossed. However, before the final choice of structure type, the slope of the river must be validated with specific instruments. For a conduit with outlets, the validation must demonstrate that the measured slope does not actually exceed 5% or 6%, depending on the length of the conduit. If the validation is inconclusive, the initially-planned choice of a conduit with outlets must be modified to a type of structure adapted to the watercourse to ensure a successful free flow of fish.

Some situations increase the uncertainty associated with the use of a slope estimate at the preliminary stages of the project and therefore the risk of having to change the type of structure at the end of the project. These situations must be considered by the proponent as, regardless of the method used, he or she remains responsible for compliance with all of the Regulation’s conditions.

In more uncertain situations, it may be advantageous to immediately select a type of culvert that will comply with the Regulation regardless of the slope of the watercourse and the length of the structure (wood culvert, arch culvert, bridge, etc.). This is especially important because the substrates of watercourses with a steep slope  are generally coarser, which can lead to excavation difficulties and even compromise the proper burial of a conduit with outlets, which is an essential condition to ensure the free flow of fish. Coarse substrates may, however, be an advantage to the stability of other types of structure.

Figure Schedule 9A Placement of thresholds used to measure the slope of a watercourse

Figure Schedule 9B Measuring the slope of a watercourse

3

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”.

The distance between the conduits of a culvert with parallel conduits must be considered when calculating the narrowing of the natural width of the watercourse by the culvert. The minimum distance between the conduits is one metre, as specified in section 102 of this Regulation.

4

Additional information

Outlet materials must be corrosion-resistant. For example, the welded joints must be galvanized to prevent rusting.

Figure Schedule 10A Location of outlets in a conduit

5

Figure Schedule 10B Characteristics of outlets in a conduit

6

Additional information

The elevation of the thalweg and the invert of conduits with outlets must be measured with accurate instruments (precision sight level, an integrated set of measuring instruments that automatically measure both angles and distances during a land survey, etc.).

Figure Schedule 10C Burial depth of a conduit equipped with outlets compared to the thalweg and characteristics of the energy dissipation basin

7

Additional information

The elevation of the thalweg and the invert of conduits with outlets must be measured with accurate instruments (precision sight level, an integrated set of measuring instruments that automatically measure both angles and distances during a land survey, etc.). 

Figure Schedule 10C Burial depth of a conduit equipped with outlets compared to the thalweg and characteristics of the energy dissipation basin

8

Additional information

The energy dissipation basin absorbs the energy and turbulence of the water leaving the culvert and provides a rest area for fish. If there is no natural basin downstream of the conduit, one must be created by excavating the watercourse bed. The bottom and sides of the basin must be stable, to avoid scouring. Where necessary, they must be stabilized with riprap. The geotextile membrane must be placed on the sides of the basin, anchored under the riprap, not under the riprap at the bottom of the basin. The space occupied by the riprap must therefore be considered when digging the energy dissipation basin, so as not to reduce its volume. The control threshold at the basin exit must not be altered by the work.

Figure Schedule 10C Burial depth of a conduit equipped with outlets compared to the thalweg and characteristics of the energy dissipation basin

9

Figure Schedule 10D Installation slope of a conduit equipped with outlets

10

Additional information

If the conduit with no outlets is placed higher than the conduit with outlets, the water is concentrated in the conduit with outlets during low flow periods. This ensures an adequate water level in the conduit with outlets. The outlets create a series of thresholds and basins in the culvert to maintain a fast enough flow and sufficient depth of water to ensure the free flow of fish.