Calculating the Water Year: Annual Snow Surveys

Snow surveys are conducted every January, February, March, and April. The Watershed Center surveys three courses located in the Trinity Alps Wilderness area. A small team of between two and four backcountry skiers travel to each of the survey locations at Shimmy Lake, Red Rock Mountain, and Bear Basin.

These snow survey sites have been measured in exactly the same locations since the 1940s. The surveyors take snow samples by plunging a specialized snow tube (a “Mt. Rose snow sampler”) deep into the snowpack 10 times along a designated transect.

The surveyors drive the snow sampler until they hit the ground, measure the height of the snow, then carefully extract the tube from the snowpack, and weigh the snow-filled tube using a handheld scale. By using the height and weight of the snow, surveyors are able to calculate the “Snow Water Equivalent” or “SWE” for short. 

With a suite of nearly a dozen survey courses established throughout the Trinity River Watershed, the combination of these valuable data make it possible for water managers to make informed decisions about potential floods, the amount of water that can be held or released from Trinity Dam, the amount of water that should be diverted to the Central Valley Project, the length of the summer forbearance period, and other decisions that fluctuate depending on whether it was a wet or dry year.

A great deal of preparation goes into each snow survey, particularly in assessing conditions for safety (avalanche and weather forecasts), cleaning and stocking Fosters Cabin (our crew’s home base for these overnight trips), completing skills training prior to surveying, and coordinating with our partners. These surveys would not be possible without the shelter of Fosters Cabin. Please help us take care of this extremely valuable resource. 

Many people inquire about snow surveys, wishing to join the team. However, backcountry travel in winter comes with heightened risks, necessitating that participating staff have avalanche avoidance and rescue training, adequate snow equipment (backcountry ski setup), safety gear (beacon, probe, shovel, GPS beacon), expert-level “survival” skiing ability, and sufficient mental and physical stamina to tackle long days and highly variable conditions in the short daylight hours of the winter months.