Stormwater Spotlight: How to Manage Your Meltwater in Washington


Stormwater Spotlight: How to Manage Your Meltwater in Washington

As warmer weather comes, it is important to prepare for an influx in stormwater coming from melting snow and ice. This stormwater can have immense impacts on stormwater systems because of the unique source and the landscape of Washington state. The Cascade Range and Olympic Mountains are ideal climates for high production of snowfall in the winter. As the weather warms and this snow melts, gravity pulls it into the low elevations that lay around and between these ranges. These lowlands, two distinct regions around the Puget Sound and Tri-Cities, act as bowls that pool stormwater from their own snowmelt as well as the higher mountains. Low lying areas face the brunt of snow and ice buildup that occurred over periods of months suddenly being released in a short amount of time. Excessive stormwater from snow and rain racing into the lowlands can cause flooding if stormwater systems are not prepared. Inspecting and cleaning your system before snowmelt begins is the best way to make sure stormwater systems are prepared for the flow. If you are uncertain where to start, follow our Spring Cleaning For Stormwater Facilities checklist.

Snow can also increase pollution risk due to the high concentration present. Pollution concentrations are higher in snow for multiple reasons. First, as snow is forming it absorbs aerosols and organic pollutants from the air [1]. After the snow has fallen and until it melts, there is constant buildup of airborne pollutants on the snow piles [2]. The highest pollution concentrations can be found at the bottom of snow piles. Over the snow season these sections repeatedly experience freeze-thaw cycles that concentrate soluble pollutants as water escapes, leaving heavy particles that are unable to be carried behind [2]. This makes the last snowmelt the most polluted, and an important time to monitor stormwater systems for clogs and trash buildup.

Typical warm water SCMs do not work with the cold water runoff from snow and ice that northern climates face due to the presence of ice, cold water, highly concentrated pollution and lack of biological activity [3]. This makes it crucially important that stormwater systems are compliant with local and state regulations, as well as EPA regulations. More information on state and local regulations on our State & Local Stormwater Standards page. Here are some common challenges to the design of runoff management practices in cold climates according to the Minnesota Pollution Control Agency [4]:

Climatic Condition SCM Design Challenge
Cold Temperatures  

-          Pipe Freezing

-          Permanent pool ice covered

-          Reduced biological activity

-          Reduced oxygen levels during ice cover

-          Reduced settling velocity

Deep Frost Line  

-          Frost heaving

-          Reduced soil infiltration

-          Pipe freezing

Short Growing Season  

-          Short period to establish vegetation

-          Different plant species appropriate to cold climates than moderate climates

Significant Snowfall  

-          High runoff volumes during snowmelt and rain-on-snow

-          High pollutant loads during spring melt

-          Other impacts of road salt/deicers

-          Snow management may affect SCM storage

 

 

Innovations have been made in parts of Washington to deal with the dramatic affect snowmelt has on the state. One such place is Spokane. For over two years there has been a $200 million stormwater project underway; the largest infrastructure project of the region. More than 20 stormwater retention tanks have been placed throughout the city, with some able to hold upwards of 2 million gallons of water each [5]. These tanks are anticipated to stabilize outfall rates, as well as prevent upwards of 71 million gallons of untreated water from being released into the river annually [5]. These efforts are intended to help the region comply with the rigorous environmental discharge standards of the Spokane River. In March of 2019 construction was in final stages when the snow melts hit. Although the project was not fully complete, functioning sections held and were successful through the melting season.

It is important to adapt infrastructure and management strategies to accommodate differences in climate, ecology, and other environmental factors that affect stormwater. If you would like a professional assessment of your stormwater facility, please reach out to AQUALIS for a free estimate and consultation. It would be our pleasure to assess  your stormwater facilities!

WA Metlwater - Snowfall covering a catch basin

References

[1] Y. Nazarenko, S. Fournier, U. Kurien, R. B. Rangel-Alvarado, O. Nepotchatykh, P. Seers and P. A. Ariya, "Role of snow in the fate of gaseous and particulate exhaust pollutants from gasoline-powered vehicles," Science Direct, vol. 223, pp. 665-675, 2017.
[2] G. L. Oberts, "Influence of Snowmelt Dynamics on Stormwater Runoff Quality," Watershed Protection Techniques, pp. 55-61.
[3] "Cold climate impact on runoff management," Minnesota Pollution Control Agency, 2019. [Online].
[4] "Challenges to the Deisgn of Runoff Management Practices in Cold Climates," Minnesota Polluciton Control Agency , 2020. [Online].
[5] K. Hill, "February’s melting snow hits nearly completed $200 million stormwater tank project in Spokane," The Spokesman-Review, 2019.