Green Stormwater Infrastructure (GSI) is widely used throughout the largely temperate climate of the Pacific Northwest. However, not all areas of the region are as temperate, and as we are seeing more extreme weather events, we need to consider how GSI may react to more sustained exposure to cold, ice and snow, as well as heat and drought.
Studies around the world have been performed on the performance of GSI facilities in cold climates. Winter runoff conditions, including frozen ground, snow cover, and ice/snow melt events have the potential to adversely impact the performance of GSI, compounded by the addition of sand and chemical deicers to runoff pollutants of concern. In short, a colder climate can impact GSI in a variety of ways.
For instance, a cold climate may result in educed infiltration capacity for GSI. Although frost penetration does not necessarily equate to no permeability, ice lenses may still form, restricting infiltration. Additionally, rain and snowmelt events may reduce or eliminate frost depth in filter media present before and after events; however, larger snow melt events on frozen ground can result in increased runoff.
A colder climate can also reduce the effectiveness of treatment from vegetated systems as the biological function tends to “turn off” in the winter when the vegetation goes dormant. Cold climate regions may also have a shorter growing season, so plant establishment may be more challenging. The effectiveness of other treatments may be similarly reduced—for instance, there may be less sediment removal due to reduced settling velocities in colder water. All of these impacts must be considered in the design and selection of infiltrating best management practices.
Designers may need to include some additional considerations when selecting specific GSI solutions, such as potentially providing larger facilities in cold climates for snow storage and meltwater infiltration as long as road salt and deicing chemical usage is limited. However, the use of GSI still yields the most cost-effective benefits to stormwater runoff management, even in cold climates.