Snowmelt: Stormwater’s Evil Twin

07 March 2019

BY Suzie Housley

Snow. It’s so pretty when it first falls. It also does not immediately rush into local waters, so sometimes we forget that snow is stormwater too! In fact, snow can actually be worse than normal, which is why we’ve dubbed it stormwater’s ‘evil twin’. Allow us to explain:

Image: Boston Globe

Frozen Ground = No Infiltration

When it snows, it tends to be cold. Freezing, in fact! In many cases the ground tends to be frozen as well, so even when it does warm up enough for the snow to melt, the water does not infiltrate like it would during normal circumstances. This can lead to a larger than normal volume of stormwater runoff entering the system, and it may also lead to increased flooding if a large amount of snow melts at once.

Image: Vermont State Police Department

Longer Residence Time = Larger Pollutant Load

The beauty of that fresh fallen snow wears off pretty quickly. Anyone living up north can attest to this! By March, there are usually piles of yellow, brown, or even black snow lining the streets and sidewalks. Unlike stormwater, which flows quickly into conveyance systems, snow can linger for days, weeks, or even months. It’s basically just hanging out and collecting all the pollutants it contacts. When it finally warms up enough to melt, this concentrated mix of pollutants hits local waters all at once, and that rush of chemicals can cause some major damage.

Image: Minnesota Stormwater Manual

Transportation Concerns = Increased Contact with Chemicals

No one wants drivers to be sliding off the road or pedestrians to be falling over on icy sidewalks. So, during the winter we must balance risks. Unfortunately, keeping the public safe has come at the expense of water quality. As snow is plowed off roads and sidewalks, it is piled together with the excess salts and chemical treatments applied to those surfaces. When the snow melts, all of that concentrated material flows over the treated surfaces again, often picking up even more chemicals on its way to local waters where it can be a significant threat to the local ecosystem. Nearly 40% of U.S. streams are reported to have chloride levels that are unsafe for aquatic life.

Recently, many regions have begun to address this problem by focusing on the proper use of road salts and other chemicals, in particular, the idea that while some might be necessary, more is not necessarily better (kinda like that whole fertilizer thing…).

Image: Chesapeake Stormwater Network

Programs like proper salt management are just part of the growing trend focusing specifically on the unique challenges involved with winter stormwater management. In addition to preparing for stormwater’s evil twin, cities are beginning to take other proactive measures, such as selecting salt tolerant species for incorporation into green infrastructure, and studying the impacts of the freeze/thaw cycle on pavement alternatives such as permeable pavers.

At StormSensor, we’re up for the challenge! Our system of networked sensors and cloud-based software allows you to track what’s flowing through your system 24/7, rain or shine (or snow!). With continuous monitoring, you can track changing trends and identify how they are affecting your stormwater system in real-time. For example, you can pinpoint the timing of a pulse of snowmelt hitting a local waterbody so you can plan timely field sampling and track impacts on the receiving waterbody.

Image: StormSensor; view from Terrapin™ cloud-based software

Contact us if you are interested in learning more about using StormSensor to track real-time flows and temperatures throughout your stormwater system. We would love to help!