Glossary of Snow Fence Terms
Attack angle (a): the angle between the prevailing transport direction and the alignment of the roadway (Tabler 1994).
Bottom gap: a space between the ground and the bottom edge of a snow fence. The bottom gap reduces deposition of snow in the immediate vicinity of the fence (Tabler 1994).
Fetch (F): the length of the area that is a source of blowing snow to a downwind location. The upwind end of the fetch is any boundary across which there is no snow transport, such as forest margins, deep ditches, tree rows and shorelines of unfrozen water bodies (Tabler 1994).
Porosity: the fraction of open spaces in the snow fence, where 0% is a solid fence and increasing values indicate lower density. This does not include the bottom gap.
Prevailing transport direction: the mean wind direction that corresponds to the direction of greatest snow transport.
Relocation coefficient: the proportion of winter snowfall water equivalent that is relocated by the wind. It excludes snow retained by vegetation, topographic features and snow that hardens or melts in place (Tabler 1994). For Minnesota, this value ranges from 0.1 to 0.7.
Seasonal snow transport (Qt, ave): the mass of blowing snow that is transported by the wind over the snow accumulation season per unit width across the wind (Tabler 1994).
Setback distance: the distance between the fence and the road shoulder as measured in the direction of the prevailing transport direction (Tabler 1994). All setbacks for living snow fences are measured perpendicular from the edge of the highway right-of-way line to the nearest row the snow fence.
Snow accumulation season (SAS): the season of drift growth, beginning with the first blowing snow event that causes drifts persisting through the winter, and ending when snowdrifts reach their maximum volume (Tabler 1994).
Snowfall water equivalent: the ratio of liquid precipitation to snowfall. Higher ratios indicate wet snow events (high liquid water content) while lower ratios represent dry snow events (low liquid water content). This varies geographically and throughout the winter season in Minnesota. The November - March statewide average is 0.10 (10 inches of snow is equivalent to 1 in of water).