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Slope Stability

Heavy rainfalls and high-volume snow melt can result in slope failures from time to time. Landslides have occurred in the District of Mission in the past, and property owners should be aware of the warning signs and preventative measures they can take.

Living and Working Near Gullies and Steep Slopes in the District of Mission

October 2011

Landslides have occurred within the District of Mission and have resulted in considerable loss of property and impacts to public infrastructure. They usually occur as a result of heavy rains or snow melt. Although not always the case, signs of instability usually precede an actual slope failure. Property owners should monitor their property for signs of instability before, during and after heavy rains. These signs can include:

  • Cracks in foundations or concrete patios;
  • Leaning deck posts or excessively sloping decks;
  • Slumps or slides in stream banks;
  • Erosion and soil exposure on slopes;
  • Fence posts or trees that are leaning downslope or upslope;
  • Cracks or soft spots in the ground near the top of and on slopes;
  • Trees with a strongly curved (“J”) shape at their base;
  • Outbreaks of springs where there were none before;
  • Undercutting of stream banks by creeks at the base of gullies;
  • Presence of water loving plants on slopes – skunk cabbage, horse tail, devil’s club etc.;
  • Retaining walls which have deteriorated due to soil movement.

Property owners can take several steps to reduce the likelihood of slope stability problems affecting their property, including:

  • Hiring a geotechnical engineer to complete regular stability assessments of their property and implementing the engineer’s recommendations;
  • Ensuring water from downspouts, driveways, lawns, decks etc. is directed away from steep slopes or conveyed to the base of the slopes in solid walled pipe.
  • Refraining from dumping yard debris, such as brush, leaves and grass clippings onto steep slopes;
  • Ensuring that retaining walls, swimming pools, ponds etc. on or above steep slopes are designed by an engineer;
  • Ensuring that any fill materials used in yard construction are designed by a geotechnical engineer and placed under his or her supervision;
  • Maintaining appropriate setbacks for fill placement or construction from the top of steep slopes as directed by a geotechnical engineer;
  • Having a geotechnical engineer assess steep slopes for appropriate vegetation cover and adequate slope stability measures;
  • Only removing or topping trees on a slope with approval by a qualified professional arborist in consultation with a geotechnical engineer.

Geotechnical engineering firms can be found in the Yellow Pages. District engineering staff is available to answer any questions, please contact:

Barry Azevedo, Manager of Environmental Services
604-820-3737