Snow fences for drifting driveways: how far upwind, how tall, and what they cannot do

Why does snow drift across the same part of the driveway?

Because the snow on your driveway after a windy day did not fall there. Wind picks up loose snow from open ground, carries it along the surface, and drops it wherever the wind slows: behind a tree line or a building, in a low spot, at the edge of a cut. Wisconsin's highway maintenance manual notes that the snow blowing onto a road can be hundreds of times what falls on it directly. A driveway beside an open field fills in at the same few places, storm after storm.

The open land is in the north of the county: in Ray Township, Armada Township, Bruce and Lenox townships, fields run right up to long driveways. The nearest long wind record, at Selfridge Air National Guard Base in Harrison Township, shows west as the most common winter wind direction, with nearly 6 in 10 winter winds of 15 mph or more blowing from between southwest and northwest. So a driveway with an open field on its west side is the classic drift problem, though your own drifts are the best evidence.

How does a snow fence work?

A snow fence does not stop the wind. It slows it, so the snow drops out in the calmer air, mostly downwind of the fence, instead of on your driveway. The working rules come from Ronald Tabler's Snow Fence Guide for the Strategic Highway Research Program:

• Porosity: 40 to 50 percent open works best. The classic wood slat fence is about 60 percent open and stores about 10 percent less snow.
• Height matters most. A 6-foot fence stores more than twice as much snow as a 4-foot fence, so one tall row beats several short ones.
• Bottom gap: about 10 percent of the total height, roughly 6 inches under a 4-foot fence, measured from the top of the winter grass. A buried fence stops working well.
• The drift: behind a 50 percent fence it grows to 1 to 1.2 times the fence's height deep and 30 to 35 times its height long.

Where should a snow fence go?

Upwind of the driveway, square to the drifting wind, and far enough back that its full drift stops short of the pavement. Tabler's rules for flat ground:

The end extension, 0.6 times the setback, catches winds up to 30 degrees off the main direction.

• Angle. Up to 25 degrees off square to the drifting wind is acceptable.
• Too close can be worse than none. A fence 40 feet from the driveway works only until its drift grows past 40 feet. University of Minnesota Extension warns that fences placed too close can leave heavy snow on roads and buildings, and Wisconsin's manual notes that improper designs can make drifting worse.

Do living snow fences work?

Yes. The Minnesota Department of Transportation pays landowners for living snow fences of trees, shrubs and native grasses, and says they typically sit 100 to 200 feet or more into the field. Tabler's guidance:

• Set back 15 times the mature height, or 35 times the height of the structural fence you would otherwise need, whichever is greater.
• At least three staggered rows, with no gaps, which funnel the wind.
• Expect several years before the plants catch snow. A temporary fence can work meanwhile, placed so its drift does not bury the young plants.

Deciduous shrubs are much less dense in winter, University of Minnesota Extension notes, so a row of evergreens such as spruce keeps more of its density. A farmer next door may offer the cheapest fence of all: Tabler's guide says six to eight rows of standing corn, set back 35 times their height, make an effective seasonal fence, and MnDOT pays farmers to leave them standing.

How do you put up a temporary plastic snow fence?

1. Set the posts before the ground freezes, as Wisconsin's highway maintenance manual advises.
2. Use steel posts about 8 feet apart for a 4-foot fence, as Tabler advises, and brace each end post with a second post driven in at an angle.
3. Pull the fencing taut and fasten it well at every post; most plastic fencing cuts easily where it rubs.
4. Leave the bottom gap, about 6 inches for a 4-foot fence.
5. Choose black, which Tabler notes resists sun damage better than other colors, and stay at 4 or 5 feet: posts alone are usually impractical for temporary fences much taller than that.

Whose land is it on, and who has to agree?

At 35 times its height, the right spot for a fence is often in someone else's field. Get the owner's written permission, agree on dates to put it up and take it down, and remember that the drift sits on their land until spring. Wisconsin's highway manual tells counties to get the owner's approval first. Check with your township's zoning office before building anything permanent, and keep fences and drifts out of the road right-of-way and the sight lines at the end of the drive.

What can a snow fence do, and what can't it?

It can catch snow blowing off open ground before it reaches the driveway. At highway scale it pays: Tabler estimated that removing snow mechanically costs about 100 times more than trapping it with fences.

It cannot stop the snow that falls straight onto the driveway, help with wind from a direction it does not face, or keep working once its drift is full. The drive still needs driveway plowing after every storm. Mark the edges and culverts first (driveway markers), keep the blade high on stone (gravel driveway snow removal), and plan the rest with long rural driveway snow removal.