By Erik Mickelson, Field Manager
Can you predict how muddy your favorite trails will be this spring? In a way, yes.
The Snow Water Equivalent (SWE) can be useful as a gauge for estimating the water from snow melt onto trails, since snow melt is analogous to a rain event. The SWE “is the amount of water contained within the snowpack…as the depth of water that would theoretically result if you melted the entire snowpack instantaneously,” explains the Natural Resources Conservation Service. In the winter these melt (or rain) events can make for soggy trails–assuming it all melts “instantaneously.”
Water trapped in frozen soils holding autumn rains and freeze/thaw event moisture may add to the SWE flows unleashed during snow melt. If the soil was near its water holding capacity (field capacity) at freezing, or between SWEs, there’s a good chance the trails could be wetter than anticipated from snow melt alone.
So how long will you be slogging through mud? The rate trails dry after rain is a function of many factors. Other than grades, outslope, and trail soil profiles, two factors that help dry trails are evaporation and transpiration from plants. The two together are called evapotranspiration, or ET. ET rates from late fall to spring are low, while SWE flows can by high, making for muddier trails.
If you decide to get out on the trails this spring, take a mental note of the good and bad trails after rain events–and save the wet ones for later.
Want to learn more? Check out this interactive SWE map and zoom in on your location.