31. Every person installing a culvert in a watercourse or a fish habitat shall ensure that the end of the culvert extends beyond the base of the fill supporting the road without exceeding 30 cm and shall stabilize that fill. Except for rectangular culverts made of reinforced concrete, he shall also backfill above the culvert up to a height equivalent to the diameter or span of the culvert divided by 4, plus 30 cm, for culverts with a diameter or span of 600 mm or less, or equivalent to the diameter or span of the culvert divided by 4, with a minimum of 60 cm for culverts with a diameter or span of 700 to 3,600 mm, or at least 1.5 m for structural plate culverts whose diameter or span is greater than 3,600 mm.