Sat. Jan 18th, 2020


The Emerald City

Let it Snow: How City Light Snowpack Study Guides its Hydroelectric Production

2 min read
The team preparing to take a snowpack sample

The expansive Cascade Range serves as a backdrop throughout
the Western U.S. With its iconic peaks piercing the sky; it’s no wonder that
travelers from across the world visit the range each year. But the Cascade
Range, specifically the North Cascades and the Canadian Cascades, is also vital
to the success of Seattle City Light and its production of clean hydropower.

Each spring, the range’s melted snowpack, or runoff flows down into a system of reservoirs that power the utility’s Skagit Hydroelectric Project. City Light monitors the water levels closely to ensure that the project operates at full capacity while meeting specific reservoir-level requirements under its federal license. These water levels are essential for flood control, the protection of salmon spawning habitats, recreation and energy production.

This delicate balance requires precise planning and
forecasting by City Light and its partners to keep the environment safe and the
generators running. Part of this planning requires helicopters, warm clothes
and snow…lots of snow.   

Weighing the snowpack sample tube

To prepare for the anticipated spring runoff, City Light
partners with the USDA’s Natural Resource Conservation Service to make the
excursion to multiple peaks and passes at varying elevations across the Cascade
Range throughout northern Washington and southern British Columbia to measure
the level of the snowpack, a practice dating back to the 1930s. The surveyors
aim to reach the locations via helicopter, some as high up as 6,000’ starting during
the last week of December, monthly through the last week of April, weather
permitting. Using a large aluminum tube, the teams take snow samples deep
through the snowpack until they hit the solid ground below the snowpack. They
then extract the tube sample out of the snowpack and weigh the tube. The weight
of the snowpack in the tube is recorded and City Light then converts that into
the forecasted water runoff. All told, the teams collect samples during five ends
of the month studies, including locations in British Columbia since 40% of the Skagit
Hydroelectric Project’s drainage area is in British Columbia. (Historically, only
approximately 25% of the runoff volume comes from across the border.)

Ole Kjosnes, City Light’s senior power analyst, has spearheaded
the testing on behalf of the utility for decades. For him, this work is not
only a keystone to the success of City Light, it also helps the utility prepare
for possible challenges in the future. 

“We’ve noticed that the runoff is happening earlier than in
the past, so we have to prepare for the runoff to meet our needs. Overall,
there was more snow in the 50s through 80s compared to the last 20 years. If
that trend continues, we will need to adapt. 

Above all, the snowpack study determines how we operate the entire
system. You can’t operate our system without it.”

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