Riverbanks, littoral zones and flood plains

The minimum standards in this section apply to settlements and buildings adjacent to lakes and waterways. The zoning by-law applies to all lakes and regular or intermittent flow waterways.

Important: No minor variance can be granted for construction work carried out in a zone where land use is subject to special constraints for reasons related to public safety (flood zones).


In principle, all structures, undertakings and works are prohibited on riverbanks. However, the following structures, undertakings and works may be authorized, if they are not incompatible with other protective measures recommended for floodplains:

  • The maintenance, repair and demolition of existing structures or works.

  • The construction or expansion of a main building when the size of the lot does not allow the construction or expansion of said building following the establishment of a riverbank protection strip and when the lot is not located in a zone with a high risk of erosion or landslides, as shown on the land use and development plan.

  • The construction or erection of an auxiliary or accessory building such as a garage, garden shed or pool, is possible when it sits on a property without excavation or backfilling, only on that part of the riverbank that is no longer in a natural state, should the dimensions of the lot no longer allow the construction or erection of said building, following the creation of a riverbank protective strip.

  • Sanitation cutting

  • Cutting required for an authorized structure or work

  • The cutting, pruning and trimming required to create an opening measuring 5 metres wide and providing access to a body of water, when the riverbank’s slope is less than 30%, as well as the construction of a trail or stairs leading to the body of water.

  • To restore permanent and sustainable vegetation, seeding and planting species of vegetation, trees or shrubs, and the work required to this end.

  • The erection of fences.

  • Any septic installation complying with by-laws on the evacuation and treatment of wastewater from isolated residences in keeping with the Environment Quality Act.

  • When the slope, soil type and land conditions do not make it possible to restore the vegetation cover and natural character of the riverbank, projects and works of plant or mechanical stabilization such as drywall or gabion, or retaining walls, giving priority to the technique most likely to facilitate the eventual establishment of natural vegetation.

  • Facilities for the withdrawal of groundwater, developed in compliance with the by-law on the withdrawal of water and its protection.

  • Undertakings and works required by structures, undertakings and works authorized in the littoral zone.

Littoral zones

In principle, all structures, undertakings and works are prohibited in littoral zones.

However, the following structures, undertakings and works can be authorized if their execution is not incompatible with other protective measures recommended for floodplains:

  • docks, shelters or landings on piles, or produced from floating platforms.
  • encroachment on the littoral zone required to carry out work authorized on the riverbank.
  • the maintenance, repair and demolition of existing structures and works.   


To find out if the by-law on floodplains applies to your property, refer to the ratings on the table in Appendix C (attached).

At all times, consult a land surveyor for the application of these ratings.

High-velocity zones (0-20-year recurrence)
In principle, in high-velocity floodplains as well as floodplains identified without distinction as to high or low velocity, all structures, undertakings or works are prohibited, with the exception of structures, undertakings and works required to maintain the land in good condition, as well as to maintain, repair, update or demolish existing structures or works, provided that these do not increase the surface area of the property exposed to flooding. The addition of a storey or cantilevered section above the 100-year recurrence rating is permitted. All other regulatory measures apply.

In addition, reconstruction is authorized when a structure or work has been destroyed as a result of a catastrophe other than flooding. 

Low-velocity zone (20-100-year recurrence)
In a low-velocity floodplain, all structures and works that are not flood-proofed as well as backfilling work other than that required to flood-proof authorized structures and works are prohibited.

Consequently, no ground floor as well as no opening (window, window well, access door, garage, etc.) must be reached by 100-year flood levels. As well, for any structure or part thereof located beneath the 100-year flood elevation level, a study must be produced to demonstrate the structure’s ability to withstand this flooding. Finally evacuation drains must be fitted with check valves.

In low-velocity zones, backfilling the land must be limited to providing immediate protection around the targeted structure or work and must not be extended to the entire property on which it is to stand: the average slope, from the top of the backfill adjacent to the protected structure or work, to its base, should not be less than 33% (vertical/horizontal ratio 1:3).

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