Snow days: time to learn more about cold climate green infrastructure

Posted in: Environmental, Municipal, Water

Snowy downtownLiving in some portions of the Pacific Northwest, residents typically enjoy a more temperate climate. This type of climate is perfect for vegetated treatment systems to manage urban stormwater runoff. As such, Green Stormwater Infrastructure (GSI) is widely used throughout this region, with a corresponding increase in knowledge of design standards and performance. We’ve written about GSI and stormwater trends before.

However, not all portions of the Pacific Northwest are as temperate, especially east of the Cascade Mountain Range where annual temperatures have a larger range and varied precipitation. 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. We can learn a lot from our colder climate friends about the best way to consider variations in seasonal performance of GSI.

Studies have been performed around the world 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.

Reduced infiltration capacity may be one way a cold climate may impact GSI. Frost penetration does not necessarily reduce filter media permeability to zero, although ice lenses may form and further restrict infiltration. In some instances, it has been observed that 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 impacting design flowrates through the media. These tradeoffs in the effectiveness of this design component must be considered in the design and selection of best management practices that target infiltration.

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. Other treatment effectiveness may be reduced—for instance, there may be less sediment removal due to reduced settling velocities in colder water.

Some GSI facilities can offer open space for snow storage and meltwater infiltration as long as road salt and deicing chemical usage is limited. Taking into account both the benefits and the challenges of GSI, it turns out that GSI provides stormwater management solutions that are the most cost effective in cold climates as well as warm ones. Designers just need to include some additional considerations when selecting specific GSI solutions, and potentially may need to oversize facilities in cold climates. However, it can be done and the benefits (including for communities) are often well worth the effort.

Kari Nichols, PE

About the Author

If a raindrop falls on the project, Kari Nichols, P.E., gets involved to find a stormwater management solution. “I believe in dedication and follow-through,” she says. “Deciphering regulatory language and developing workable design solutions helps me connect with clients and colleagues.” Kari has a taste for adventure and a passion for sustainability, which she satisfies by exploring natural and urban environments.

Read more posts by Kari Nichols, PE

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