|Length of conduit (L)||Maximum slope of watercourse at the site of crossing1||Minimum diameter of conduit (mm)||Burial of conduit over its entire length2||Maximum narrowing of the width of the watercourse4|
|Proportion of diameter||Minimum||Maximum||Slope5 upstream > 1%||Slope5 upstream ≤ 1%|
|0 < L ≤ 9 m||2%||600||30%||250 mm3||500 mm||20%||50%|
|9 < L ≤ 12 m||2%||750||30%||250 mm||500 mm||20%||50%|
|12 < L ≤ 18 m||1%||750||20%||250 mm||500 mm||20%||20%|
|18 < L ≤ 24 m||0.5%||750||20%||250 mm||500 mm||20%||20%|
1The slope is the inclination of the section of the watercourse included between the first natural tresholds 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 treshold.
2The depth of the burial to the invert downstream is measured with relation to the thalweg of the treshold of the natural bed of the watercourse, located at a distance of over tree times of the conduit downstream. The slope of the conduit will be the same as the slope of the watercourse.
3Except 600-mm diameter conduits that must be buried at a depth of 180 mm.
4The width of the watercourse is measured at the level of the upper limit of the banks.
5Corresponds 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 conduit.