A snow fence is a specialized barrier designed to control where wind-driven snow accumulates rather than blocking it entirely. It is primarily used to protect infrastructure and property from deep drifts. The fundamental goal is to manipulate the aerodynamics of the prevailing wind, forcing the snow to deposit in a pre-determined area. By engineering where the snow lands, these fences significantly reduce the need for costly mechanical snow removal from roadways and other installations.
The Aerodynamic Principle of Snow Fences
Snow fences function by altering the wind flow rather than simply acting as a solid wall. As wind carrying snow particles approaches the fence, the barrier creates a localized zone of reduced wind pressure and velocity on its downwind, or leeward, side. This reduction in speed is the mechanism that causes the airborne snow to drop out of the airstream.
Wind possesses kinetic energy necessary to keep snow particles suspended or moving via saltation, where they bounce along the ground surface. When the wind passes through the porous fence, its speed drops below the threshold required to maintain this snow transport. The sudden loss of energy means the wind can no longer carry its snow load, and the particles fall to the ground, forming a drift. This accumulation process begins close to the fence and extends downwind, creating a large, engineered snowdrift that traps the snow before it reaches the protected area.
Key Design Factors for Effectiveness
The successful operation of a snow fence depends on three engineered variables: porosity, height, and placement distance. Porosity refers to the ratio of open area to solid material; effective fences are not solid barriers. A porosity range of 40% to 60% is recommended because it allows air to bleed through. This prevents the extreme turbulence that would otherwise cause a drift to form right at the base of the fence and quickly bury it.
The fence’s height directly influences the size of the snowdrift it creates. A common rule of thumb is that the maximum length of the resulting drift, measured downwind from the fence, can be as much as 30 to 35 times the fence’s height. This relationship is a fundamental consideration for snow storage capacity, as a taller fence can trap significantly more snow.
The height-to-drift-length ratio determines the critical placement distance. The fence must be positioned far enough upwind from the object it is protecting, such as a road or rail line. This ensures the entire resulting snowdrift forms between the fence and the protected area. Placing a fence too close is a common error that can worsen the problem, causing the drift to cover the area the fence was meant to safeguard. Leaving a small gap, often around six inches, between the bottom of the fence and the ground is also beneficial, as it helps prevent the fence from being buried and maintains its effectiveness.
Common Applications and Use Cases
While their most visible application is alongside major highways, snow fences are employed across a variety of settings where blowing snow presents a safety or logistical challenge. They are commonly used to keep railway lines clear, preventing snow buildup that can interfere with train operation and track maintenance. Airports also utilize these barriers near runways to ensure clear visibility and safe operating conditions for aircraft takeoffs and landings.
Beyond transportation infrastructure, snow fences are important tools in agriculture and land management. Farmers use them to protect farmsteads, livestock areas, and access roads from deep drifts. Living snow fences, which are rows of trees or shrubs, also trap snow to increase soil moisture for crops when the snow melts, aiding in soil conservation. Fences are also strategically used in environments like ski resorts to manage and increase snow depth, or for avalanche control purposes.