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LID SWM Planning and Design Guide β

Winter

Cold Climate

The majority of Ontario has a "Humid continental" Dfb climate, which includes average temperatures in the coldest month well below -3°C. These conditions are found in many other parts of the world where LID strategies are routinely employed, including many northern states in the USA and a large swath of northern Europe.

De-icing Salt

See also: Salt management

Snow being stored on a filter strip in Markham, ON

Sodium and chloride ions in de-icing salts applied to asphalt areas travel easily with the runoff water. De-icing salt can increase the mobility of some heavy metals in soil (e.g. lead, copper or cadmium). This may increase the downstream concentration of these metals [1][2]

Very few studies have sampled groundwater below infiltration facilities or roadside ditches receiving de-icing salt laden runoff have found concentrations of heavy metals that exceed drinking water standards [3][4]

To minimize risk of groundwater or soil contamination, the following management approaches are recommended (Pitt et al., 1999; TRCA, 2009b):

Stormwater infiltration practices should not receive runoff from the following areas:

  • Where large amounts of de-icing salts are applied (e.g., busy highways), or
  • Pollution hot spots (e.g. vehicle fuelling, servicing or demolition areas, outdoor storage or handling areas for hazardous materials, and some heavy industry sites); *Prioritize infiltration of runoff from source areas that are comparatively less contaminated such as roofs, low traffic roads and parking areas; and
  • Apply pretreatment practices before infiltration of road or parking area runoff.

Other freezing related concerns

Plowing

Rubber plow blades are increasingly available and required in many jurisdictions. Their use reduces damage to all kinds of pavement surfaces and they are particularly recommended for application on LID systems including curb inlets or permeable paving.

Flow control devices

LID facilities have been demonstrated to function well throughout frozen periods of the year even when all components were fully frozen for some part of the year. However, where the consequences of even temporary ponding would be entirely unacceptable, underdrains should be placed below the frost line to reduce the threat ice clogging. Weirs are generally less prone to clogging from ice than orifices under all flow conditions, proprietary low flow devices are also available which are designed to mitigate clogging from ice or other solid debris.

Rainwater harvesting

Freezing temperatures can cause problems with pipes and cisterns exposed above the frost penetration line. This maybe a significant issue for rainwater harvesting systems, including residential rain barrels.

Green Roofs

The survival of green roof planting is greater in winters with long deep sub-zero temperatures. Being shallow and very exposed to warming sunlight, green roofs thaw rapidly. Frequent freeze-thaw cycles in the early and late winter are associated higher loss of vegetation on green roofs.


  1. Amrhein, C., Strong, J.E., and Mosher, P.A. 1992. Effect of de-icing salts on metal and organic matter mobilization in roadside soils. Environmental Science and Technology. Vol. 26, No. 4, pp. 703-709
  2. Bauske, B., Goetz, D. 1993. Effects of de-icing salts on heavy metal mobility. Acta Hydrochimica Hydrobiologica. Vol. 21. pp. 38-42., 1993).
  3. Howard, K.W.F. and Beck, P.J. 1993. Hydrogeochemical implications of groundwater contamination by road de-icing chemicals. Journal of Contaminant Hydrology. Vol. 12. pp. 245-268.
  4. Granato, G.E., Church, P.E., Stone, V.J. 1995. Mobilization of Major and Trace Constituents of Highway Runoff in Groundwater Potentially Caused by De-icing Chemical Migration. Transportation Research Record. No. 1483.