When you think of electricity being generated from hydroelectric dams, you might first picture rushing rivers that spin giant turbines. But the story actually begins on snowcapped mountains. 

Hydropower is the conversion of flowing water into electricity. Hydropower is considered a renewable energy source, meaning its fuel is replenished by nature, or more specifically in this case, by the water cycle. The water that drives the Northwest’s hydroelectric generators comes from rain and snow further upstream that falls within the Columbia River Basin – a vast area that begins in the Rocky Mountains of British Columbia and flows down through most of Washington, Oregon, Idaho and western Montana.
snip of hydropower poster - mountains and snowpack

Precipitation that falls as rain helps keep the rivers flowing in the winter and spring, but it’s the melting snow that carries us through the dry summer months. The amount of snow that accumulates high in the mountains – the snowpack – is vital to the energy needs of the Northwest and is highly variable from year to year.

Where you see snow, we see fuel

Knowing how much water is being held in the snowpack in any given year is critical to ensuring enough fuel is available to meet the region’s demands. Hydropower operators monitor daily not only the snowpack, but temperature, precipitation, storms and droughts, as well as wind and solar energy outputs. This information helps them plan for near and long-term energy availability for the Northwest.

Monitoring snowpack and the streamflow is no small feat; it requires the collaboration of multiple agencies and teams. The U.S. Department of Agriculture, Natural Resources Conservation Service and National Water and Climate Center monitor the snowpack at 300 mountain sites across Oregon and Washington. This data is available online in near real-time. BPA also funds dozens of streamflow gages to help monitor river levels and several temperature and precipitation sensors in remote locations where snowpack is particularly important for hydropower generation.

How is snowpack measured?

Snowpack is monitored either by manually sampling the snow with an aluminum tube and weighing it or by automated remote stations equipped with a device called a snow pillow. A snow pillow looks like a trampoline hooked up to sensors to weigh the snow. The automated stations also measure other weather conditions like temperature, wind speed, relative humidity and precipitation.

What does winter snow have to do with summer?

Forecasting the volume of streamflow from snowpack levels is critical and challenging. Not only does the depth of the snowpack vary a lot from year to year, but the rate at which it melts fluctuates as well. Warming winter temperatures also mean that more precipitation will fall as rain instead of snow, making the snowpack and streamflow more variable from year to year. 

Summer flows are dependent on water in storage reservoirs. Following dry winters with little snowpack, it may be difficult to refill the reservoirs, and there may not always be enough water to meet all demands on the system. The region’s hydropower operators work together to make the best use of storage reservoirs and maximize the power output to maintain reliability across the Northwest.