Conditions to meet for a culvert with a round conduit where free flow of fish must be ensured
All the conditions (width, slope, burial, narrowing, etc.) indicated in Schedule 9 must be complied with when installing a culvert with a circular conduit in a watercourse where the free circulation of fish must be ensured. 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.
The decision tree below can be used to decide on the type of structure that must be installed to cross a watercourse.
1 The slope is the inclination of the section of the watercourse included between the first natural thresholds not touched by the work (excavation, installation of conduit, rockfill, etc.) and located upstream and downstream of the culvert. It is measured from the thalweg of each threshold.
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.
Figure Schedule 9A Placement of thresholds used to measure the slope of a watercourse
Figure Schedule 9B Measuring the slope of a watercourse
2 The depth of the burial to the invert downstream is measured with relation to the thalweg of the threshold of the natural bed of the watercourse, located at a distance of over three times the diameter
Figure Schedule 9C Burial of a conduit following the slope of the watercourse
Figure Schedule 9D Burial depth for a conduit
3 Of the conduit downstream. The slope of the conduit will be the same as the slope of the watercourse. Except 600 mm diameter conduits that must be buried at a depth of 180 mm.
4 The width of the watercourse is measured at the level of the upper limit of the banks.
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.
5 Corresponds to the slope of a watercourse measured between two natural thresholds that are not touched by the work and are located upstream at a distance equivalent to twice the length of the conduit.