Natural Routes to Snow-Free Roads
Living snow fences can make winter travel safer and save millions of dollars in snow-removal costs.
By Jim Reil
Blowing and drifting snow.
For most Minnesotans that phrase conjures up images of windblown landscapes where roadways disappear, weather forecasters warn of life-threatening conditions, and highway heroes drive big, orange trucks.
One such season was the winter of 1996-97, when Minnesota suffered eight blizzards that closed schools and businesses, piled up record snowfalls of 80 to 90 inches in many areas, and set the stage for the infamous floods of 1997. Before it all melted, Minnesota taxpayers had spent $215 million removing snow from streets, roads, and highways across the state.
Even in an average winter, Minnesota taxpayers spend about $100 million for snow removal. Of that, the Minnesota Department of Transportation, known as MnDOT, typically spends $41 million. In 1996-97 MnDOT's portion went up $7 million to $48 million. The rest of the plowing bill that season -- some $167 million -- went to local governments.
A good part of the extra costs resulted from replowing windblown snow. As most snowplow drivers will tell you, the quantity of snow that blows onto the road in exposed, windy locations can be hundreds of times greater than the precipitation that falls directly on the road.
The extraordinary winter of 1996-97 led officials in MnDOT, the Department of Public Safety, and other agencies to think seriously about more economical ways to manage blowing, drifting snow and prevent recurring snowdrift problems. In February 1997 several state and federal agencies formed the Minnesota Interagency Living Snow Fence Task Force. That group quickly put together a concept paper outlining the benefits of community shelterbelts and living snow fences of trees, shrubs, and grasses on rural roads. In its elegantly simple mission statement, the task force averred: "We cannot keep it from snowing; we can influence the wind that carries tons of blowing and drifting snow."
Since then, the task force has identified about 4,000 areas around the state where a quarter-mile planting of two or three rows of trees, shrubs, and grasses would make the difference between plowing the road once and plowing it several times after every storm. Snow barriers don't come cheap: The task force estimates the cost for 1,000 miles of living snow fence at $40 million, including the cost of seedlings, labor for planting and maintenance, and purchasing easements on strips of privately owned land. Yet the potential benefits are even greater.
"Once an effective snow fence is established, we would recoup the costs in one or two bad winters, or within a few average winters," says task force member Steve Prestin, a former Federal Emergency Management Agency hazard mitigation specialist, now with Public Safety's Division of Emergency Management. Since 1993 Prestin has been assessing plans to reduce flood and storm damage in Minnesota.
"The average benefit-to-cost ratio for living snow fence projects, using FEMA guidelines, is $17 in savings for each dollar spent, assuming a 30-year life for the fences," says Prestin. "That's assuming an average winter with 32 inches of snowfall and snow removal costs calculated at just $1 per ton. In a bad winter with more snow, requiring more trucks and heavy equipment to be used more often, snow removal costs can run as high as $3 to $5 per ton in some areas.
"These figures only include savings from reduced snow removal costs. Additional savings from improved highway safety--resulting in fewer accidents, less property damage, and fewer injuries and fatalities--plus the savings to commerce with fewer transportation delays will increase the benefit-to-cost ratio by four or five times."
Drop the Snow
Highway snowdrifts form wherever the surrounding topography is higher than the road surface and open to windblown snow. It's possible to reduce drifting by raising the road surface or back-sloping the right of way, but rebuilding roads or rights of way to eliminate drifting is rarely practical, or even possible. What's more, rebuilding doesn't solve visibility problems and icy road conditions associated with blowing snow.
A second method to stop drifting is to put up a barrier, such as a structural snow fence or a living snow fence, to interrupt wind flow and allow snow to drop out before it reaches the road.
The idea of shelterbelts and living snow fences is nothing new. Pioneers planted shelterbelts to protect farmsteads on the open prairie, and as early as 1905, railroad companies started planting trees to keep snow off railroad tracks. From the 1930s through the 1950s, state highway departments, including Minnesota's, also experimented with living snow fences.
In the July - August 1956 issue of The Conservation Volunteer, Harold E. Olson, engineer of roadside development for the Minnesota Department of Highways, reported that 12 million tree and shrub seedlings had been planted along 600 miles of state highway since 1939. Olson also reported that, in the winter of 1955-56, the highway department spent nearly $1.5 million plowing snow and $323,658 on wooden slat snow fences.
"Those early attempts at living snow fence weren't all that successful," says Dan Gullickson, MnDOT urban and community forester and task force chair. "In most cases the trees were planted within limited rights of way--usually 75 feet or less from the road centerline. They effectively interrupted wind flow, but didn't allow enough distance for snow to drop out before it reached the roadway. In many instances mature trees actually increased the amount of snow deposited on the road and in roadside ditches."
Research conducted since the early 1970s has shown that it is possible to predict how much snow a snow fence will stop and store over winter. Researchers base their predictions on various factors: wind speed and direction, relative humidity, size and weight of snow particles, and fence height, length, and density (ratio of solid area to open area).
Snow fences work because most windblown snow stays within four feet of the ground, and none of it rises more than 16 feet, even with a 60-mile-per-hour wind. Once snow particles collect in a drift, they bond together and resist being blown away. A well-designed fence will collect a season's worth of snow and hold it for the duration of the winter.
Doubling the height of the fence quadruples its storage capacity. A 4-foot-high barrier with 50 percent density will hold about 4.4 tons of snow per linear foot. An 8-foot fence will store 20.3 tons of snow per foot, and a 12-foot fence will store nearly 50 tons per foot.
"That's why you rarely see those wooden slat snow fences along highways anymore," Gullickson says. "Short, 4-foot fences like that usually filled up quickly and then ceased functioning. They weren't cost effective."
Left unchecked, 50 percent of wind-borne snow evaporates within a travel distance of two miles, and 85 percent evaporates after 10 miles. "The idea that a lot of drifting snow comes into Minnesota from other states just isn't so," says Gullickson. "Snowdrifts are created with snow that falls locally, so a properly designed living snow fence can be a very effective solution for areas with chronic snow-drifting problems."
In a typical application, two parallel shrub rows, each a quarter-mile long and 10 feet high, with a 70 percent density, planted across the prevailing wind 170 to 375 feet from the edge of the road, will provide enough storage capacity to eliminate most drifting problems in an average winter. A 14-foot-high fence will provide adequate storage 95 out of 100 winters.
The most effective, long-lasting fences are planted with trees, shrubs, and grasses specially suited to the soil and climate of the site. Pine trees grow well in many parts of Minnesota, but pines eventually lose their lower branches and become less effective. Conifers such as spruce and cedar are more effective, especially on sites where only a single-row fence can be planted.
A combination of two or three rows of deciduous trees or bushes with prairie grasses offers better protection and a wider range of options than do conifer plantings. Plants such as lilac, red osier dogwood, plum, highbush cranberry, buffalo berry, hazelnut, and juneberry, along with grasses such as prairie dropseed, big bluestem, and Canada wild rye, make attractive snow barriers that will last twice as long as a structural fence--30 to 50 years or more--at about one-third the cost. Some shrubs and prairie grasses produce marketable products, such as berries, nuts, and grass seeds. They also provide habitat and food for wildlife.
Southern Minnesota has some of the best examples of living snow fence technology. Since 1984, Mark Hesse has planted five living snow fences, from one-quarter to one-half mile in length, on his farm near Mountain Lake in Cottonwood County. Alternating rows of cedar and ash trees with honeysuckle and hackberry bushes have furnished extraordinary protection, he says.
"During the winter of '96-97, one snow fence collected a drift 300 feet wide and 15 feet deep along a section line," said Hesse. "It kept our road clear enough to make it through to State Highway 30 all winter."
Next door in Watonwan County, a snow-control committee of representatives from county, state, and federal agencies; the cities of St. James and Madelia; and the Watonwan 4-H Federation has set up two demonstration projects along State Highway 60. The Highway 15 junction has a quarter-mile fence of eastern red cedar, common lilac, and late lilac. The half-mile planting at Highway 4 contains the same species.
For most roadways, and for shelterbelts intended to protect rural communities, a living snow fence needs to be planted outside the existing right of way. That usually means planting on private land--often agricultural land. Current federal and state programs that foster soil conservation, water quality, and wildlife habitat--such as the Conservation Reserve Program and Reinvest in Minnesota--offer landowners some incentives to plant living snow fences; however, payment terms and planting options don't always meet the needs of either the landowner or a long-term snow fence project.
The snow fence task force is putting together "The Minnesota Living Snow Fence Technical Guide," with technical advice and information on resources available to help communities and landowners create living snow fences.
Individual farmers and landowners need to find workable ways to implement the living snow fence project, says Pete Takash, public affairs director of the 15,000-member Minnesota Farmers Union. "To gain the trust and cooperation of landowners, local committees must include the landowners up front in the planning process," he says.
Toward that goal, MnDOT, with help from the Minnesota Farmers Union, the Minnesota Farm Bureau Federation, and local Soil and Water Conservation Districts and Natural Resources Conservation Service offices, is conducting focus groups with agricultural landowners to ask their advice on what it will take to put together a long-term, statewide living snow fence program. Such a program would offer Minnesotans an opportunity to create safer roads and save millions of dollars.
Jim Reil, DNR information officer in Bemidji since 1987, has worked for the state of Minnesota for 28 years.