Slope Stability Guidelines for Development Applications

The general intent of these studies is to assess whether or not a slope is considered to be stable and, if not, to provide a “safe” set-back distance from the slope crest behind which structures and other facilities can be constructed. Unstable slopes and the land located between the unstable slope and the set-back line are called “Hazard Lands.” In a broad sense, Hazard Lands are those at risk of being adversely impacted by any natural geologic processes. In the case of unstable slopes, Hazard Lands are those that have a factor of safety of less than 1.5 against being affected by a slope failure. In some circumstances, Hazard Lands may, in accordance with Ontario’s Planning Act, be transferred to the municipality or other agency (such as a Conservation Authority). The development of Hazard Lands is restricted. They should not be developed with permanent structures, parking or roadway areas, amenity areas (i.e., the landscaped area around a house, typically in the rear yard, that could be developed with pools or decks), septic beds, or any other valuable infrastructure. Buildable lots in a residential subdivision should not include Hazard Lands. In some circumstances, it may be permissible for properties to contain Hazard Lands, provided a separate “buildable lot” exists, that is large enough to include an amenity area, and that on its own conforms to all applicable laws (e.g., zoning, building code, etc.), and provided that the Hazard Lands are entirely contained within a separate parcel of land. In this case, restrictive covenants would be placed on title that would limit or restrict certain uses within that separate parcel (e.g., no permanent structures). In a rural setting, with large lots, a separate parcel may not be required, provided there is large separation between the structure and active use areas from the Limit of Hazard Lands.