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Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.10. Designing to Reduce Snow, Ice, and Chemical Accumulation

 

The environmental stewardship practices profiled in this section are intended to increase the roadway and bridge designer's awareness and consideration of techniques, configurations, and design parameters to reduce the amount of snow and ice accumulation, and thus sand, salt, and other chemical applications.

 

3.10.1 Designing Roads to Minimize Snow Drift
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Understanding the cause of snow drift accumulations and designing to minimize the causes can reduce the severity of an icing problem, thus lowering salt usage. A significant amount of the snow that needs to be removed from roadways is deposited through drifting. Throughout all phases of roadway development (route location, planning, preliminary design and detailed design) the designer has the opportunity to make decisions regarding the location, configuration, and design details of the facility, which will affect the potential for snow and ice accumulation and the actual application of salt throughout the life of the facility.

Benefit to cost ratios for permanent snow fences, based only on reduced costs for snow removal range from 10 to 35:1, depending on the quantity of blowing snow, according to the National Research Council. [N] It costs 3 cents to intercept and divert a ton of snow with a snow fence over the life of the fence, and $3 to plow the same amount of snow. [N] Wyoming DOT reports that with the installation of snow fences along Interstate 80, snow removal costs dropped as up to 50 percent and the accident rate during snowy, windy conditions fell by up to 70 percent. [N]

Level of service and safety are often improved as well. The Alaska Department of Transportation and public works videotaped snow accumulation on test sections of roadway where it had installed snow fences in order to extend the season in which the roadway was opened. Snow accumulation on the roadway in areas protected by the fences ranged from zero to one meter, but the accumulation on the sections of road without fence protection reached nearly three meters. In the spring, crews took two to four days to clear unprotected sections, whereas only two hours were needed to clear protected sections. Other benefits included reduced labor costs, reduced wear and tear on maintenance equipment, and a safer work environment for road crews. Drifting problems can be increased by poor roadway and bridge design and decreased by good design. By promoting the infiltration of water under pavement, snowdrifts can contribute directly to pavement damage. In addition to serving as a water source, drifts can adversely drainage by blocking ditches, drains, culverts and wildlife crossings. Reduced wind speed areas caused by changes in grade, vegetation, plowed snow banks, safety barriers, and bridge abutments can cause snow accumulation affecting the roadway and/or bridge if the obstructions are close enough to the travel lanes. Drifting can also be controlled through the erection of drift control devices such as snow fence and snow ridges at the proper distance from the road.

  • As a guiding principle, designers should consider maintenance requirements when determining the location, concept designs, preliminary designs and final designs for roadway infrastructure. Research and case studies have confirmed that there is a direct relationship between certain roadway design parameters, and snow and ice accumulation. It is possible that the incorporation of features to minimize snow and ice build up into a roadway or bridge design will add to the capital cost. However, it is also clear, however, that from a broader life-cycle view, such initiatives are likely to increase safety and reduce maintenance costs throughout the life of a roadway. These trade-offs and value engineering on a life-cycle basis should be considered as an integral part of route location, preliminary design and detailed design. .

The Transportation Association of Canada has outlined the following factors to consider in Roadway and Bridge Planning Design to minimize snow accumulation and salt usage: [N]

Example 8 : Factors to Consider in Roadway and Bridge Planning Design to Minimize Snow Accumulation & Salt Usage

Meteorological Data

Roadway maintenance staff are often familiar with local conditions and are a source of useful "hands on" information. The following meteorological data should be obtained as background information:

  • Average daily and annual snowfall.
  • Prevailing wind directions and speeds.
  • Storm directions and the amount of snowfall typical to a winter storm.
  • Mean monthly temperatures and expected winter extremes.
  • Number of freeze/thaw cycles.

Surrounding Terrain

  • The terrain surrounding a site will affect the amount of snow that can drift towards the roadway or bridge.
  • In establishing the location of a new roadway alignment bear in mind that the upwind terrain is key. The distance from the alignment to any major upwind features (e.g., a ridge, a heavy tree line, a building line, etc. ) is referred to as the "fetch". The bigger the fetch, the larger the snowdrift potential and the larger the problem on the roadway or bridge.
  • The surface of the upwind fetch area is also a major concern. A "smooth" area such as frozen water or short grass will not trap snow and hence will not assist in reducing drifting conditions. Rougher terrain, such as ploughed fields, crop stubble, long grass, shrubs or particularly mature trees with dense winter branch structure, will trap snowfall and may reduce the potential drifting conditions at the roadway or bridge.

Interchanges

Complex wind flows are associated with interchanges and usually it is necessary to conduct a model study to fully assess conditions.

  • From the point of view of snow accumulation, a roadway with a higher level of service (LOS ) should cross over roadway with lower LOS as prevailing winds would blow snow off major roadway.
  • Open style abutments should be considered over closed abutments to reduce snow accumulation, although the higher cost of open style abutments, and their typically rural nature may dictate the use of closed abutments in many instances.

Roadway Shading / Exposure to Sun

In areas of high tree cover, consider:

  • Winter altitude and azimuth (bearing, measured clockwise from true north ) of the sun.
  • Potential shadow effects of the tree cover which will affect the potential for ice melting on the road surface. Trees should be cleared back far enough to maximize the heating effect of the sun.
  • Similar considerations should be given to site conditions where vertical walls are part of the roadway design. In this case, the vertical wall should be replaced with a sloped embankment if possible.

Elevated Road on Fill Section

With divided roadways and a median width which will allow the establishment of independent grades for the two directions of travel, it is desirable to set the elevation of the upwind lanes lower than those of the downwind lanes, or at least, at the same elevation as the downwind lanes.

  • Preferably the top of pavement should be approximately 1 m above typical snow depths in the area.
  • If possible eliminate the need for safety barriers, and therefore, the obstruction that causes snow drifting with slope flattening of fill side slopes. Ideally, side slope should be flattened to 7:1 for effective snow accumulation.
  • Generally, a road cross-section totally on fill without significant terrain features upwind is more likely to blow clear of snow than any other design configuration.

Wide Ditches

Wide ditches provide storage for plowed snow which otherwise would be piled along the edge of the roadway and would promote more snow accumulations.

Use of Guide Rails

  • Box beam / cable guide rails have the least obstruction and in theory, accumulate the least amount of drifted snow but in practice, plows push snow against box beam / flex beam to create a solid barrier therefore, for the purposes of snowdrifting / accumulation, assume all barriers are solid.
  • Solid Jersey barrier is easiest to plow against.
  • Tall solid barrier has increased drifting area and increased shaded area.
  • Flex-beam guide rail, in theory, collects the largest amount of drifted snow.
  • Reduce the need for barrier at side of roadway through slope flattening.

Berms for Snow Accumulation

  • Locate berms upwind of the roadway, setback 7 times the berm height.
  • To obtain the maximum snow collection capacity, maximize the berm height and ensure berm slopes are as steep as practical.
  • One tall berm is more efficient at accumulating snow than a number of rows of shorter berms.
  • To maximize the effectiveness of tree plantings, locate trees on a berm. However, the setback should be 15 times the combined height of the berm and coniferous tree planting.

Backslope

Flatten upwind backslope (ideally 7:1 or flatter ) to minimize drifted accumulations on roadway.

  • With roadways in cut sections, consider a wider cut on the upwind side than on the downwind side, ideally meeting the 7:1 minimum gradient discussed above. If the roadway cut is a source of material for other sections of the roadway, consider taking the majority of the material from the upwind side of the cut.

Obstruction Close to Roadway

  • Obstructions that can cause snow accumulation problems are as follows trees too close to road; mail boxes; utility poles; guide rails; plowed snow banks; and fence rows.
  • Consideration should be given to eliminating / minimizing these obstructions if they are causing snow accumulation problems.
  • Where possible locate obstruction on downwind side of roadway.
  • As a general rule of thumb a 50 percent solid obstruction (snow fencing, vegetation ) should be placed a distance of 15 times its height from the edge of roadway, on level ground. A solid obstruction (buildings, double vegetation ) should be placed 10 times its height on level ground.
  • Noise walls do not typically present a problem with snow accumulation as they usually are located in residential areas that limit snow movement towards the wall and the roadway, however snow drifting at end details should be considered.

Vegetation Management

With appropriate landscape design, many snow drifting problems could be solved or lessened. Similarly, improper design or placement of vegetation can aggravate a snow accumulation problem (particularly at interchanges ).

  • Before vegetation is removed for the construction of new roadways (or for existing roadway improvements ) designers should evaluate existing site conditions in order to determine whether or not existing vegetation could prevent a snow related problem or could cause a future snow related problem. Preserving existing vegetation is more economical and time efficient than planting new vegetation. This approach also allows existing vegetation to be incorporated into new landscape plans.
  • The objective of upwind snow fences (non-living or living ) is to encourage a snow drift immediately downwind of the fence or vegetation with the result that little snow is left to drift onto the roadway.
  • Upwind vegetation planting can have a similar effect to snow fences providing the configuration and location is appropriate and the planting is not close to the roadway.
  • Plants with dense branch structure will hold snow to approximately one half its height. Trees and woody plants are better as they do not tend to bend as much under the weight of the snow.
  • Corn stalks left in agricultural fields on the upwind side can slow wind speed and reduce drifting and blowing snow. Five or six rows of corn with a similar setback to that shown in Figure 13 will be effective in reducing snowdrifts.
  • Uncut grass in the ROW is better than cut grass as it keeps snow from blowing with the exception of grass directly adjacent to the roadway, which ideally should be cut short to avoid drifts that would extend onto the roadway.
  • If there is sufficient land area available, at least 60 meters, a snowbreak forest is a viable option. However, a much more economical solution for new roadways is to retain existing forest. This saves the time required for newly planted vegetation to reach their required height. Snowbreak forests also provide substantial benefits to wildlife and may be managed for timber production.
  • As the transportation right-of-way is usually too small to accommodate the setback required for living snow fences, cornrow fences, snowbreak forests or even structural snow fences; it may be necessary to enter into land use agreements with private landowners.

Urban Considerations

In an existing urban environment, little can be practically done to reduce snow accumulation, as roadway rights-of-way are constrained and adjacent lands typically built-up; accumulated snow is removed as per the municipalities' snow removal program.

  • Snow storage in an urban environment is often a challenge and consideration should be given to providing larger cul-de-sacs, bicycle paths and wider curb lanes (especially across bridges ) for temporary snow storage, where appropriate.

Drainage

Good roadway drainage will lead to reduced ice accumulation, and as such reduced salt usage (this includes intersecting roadways and accesses as well as the main roadway ).

  • Set maximum and minimum grade to help maintain an even distribution of salt, and to allow melted ice/snow to drain to catch basin.
  • Optimize salt usage by using lower superelevation rates (to help maintain even distribution of salt ).
  • Use crowned roadways, and good crossfalls (2 percent-3 percent ).
  • Mark all culvert ends to make them easier to locate for cleaning and thawing activities.

Pavement Choice in Salt Vulnerable Areas

  • Though open friction course asphalt or grooved concrete pavements will shed surface brine more quickly, they can reduce salt spray and therefore may be beneficial in proximity to areas that are vulnerable to the effects of salt spray.

SHRP Report H-381, Design Guidelines for the Control of Blowing and Drifting Snow, also describes how to design effective and economical measures for controlling blowing and drifting snow, including various snow fence designs to accommodate land use and right-of-way considerations; considerations for pavement design and appurtenances; proper siting of snow fence to compensate for terrain; and ways to use trees and plants as natural snow fences. The field research and sources of information are included too. [N] [N]

 

3.10.2 Designing Snow Fences
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Highway segments with wide, open stretches are vulnerable to blowing snow accumulation on the surface and reduced visibility for roadway users. Traditional snow fences are designed to permit 40 - 60 percent airflow, slowing the wind and piling the snow safely downwind. The Strategic Highway Cooperative Research Program's Snow Fence Guide provides construction plans and guidelines for placement of snow fence for maximum effectiveness and cost-efficiency, as well as ways to work with landowners to obtain cooperation with a snow fence program. [N]

Consideration should be given to the use of roadside plantings or solicited cooperation from local municipalities to require land owners/developers to include plantings in their buffer zone plans to curtail drifting. Another means is to request farmers to leave corn stalks high where the land adjoins a state highway.

If properly designed, tree plantings can be as effective as structural snow fences. The requirements for effective living snow fences are the same as those for structural snow fences

  • Adequate snow storage capacity
  • Absence of openings or gaps
  • Adequate setback

Snow Fence Site Design and Placement Tools

WYDOT and NYSDOT Software

For nearly 30 years the Wyoming DOT (WYDOT) has been using snow fences to prevent blowing and drifting snow from covering roads and impairing motorists' ability to see other vehicles, reducing maintenance costs and salt application and runoff to the environment at the same time. To ease the process of determining exactly which sections of road will be affected by blowing and drifting snow and where snow fences should be placed or the topography should be changed to keep roads clear, WYDOT developed software tools based on research conducted under the Strategic Highway Research Program (SHRP). [N] The research resulted in precise guidelines for placing snow fences for maximum benefit, using average snowfall, winter temperatures, wind speed and direction, and the project site's topography. The WYDOT software handles virtually all the steps in the SHRP guidelines, from assembling the needed weather information to determining the location of a snow fence. The system has two components. The first is a set of computerized maps containing information on prevailing winds and average snow accumulations. The second component is a customized snow drift module that works with commercial roadway design software. The snow drift module, which uses the formulas in the SHRP guidelines, determines where snow drifts will form based on prevailing weather conditions and the project site's topography. The module determines if the site's weather conditions and topography will cause a snow drift to form on the road and plots the shape and location of the drift (Figure 6-1 below). If the user adds a snow fence upwind of the road, the module plots where the drift will form, showing at a glance that the fence will protect the roadway (Figure 6-2 below). Designers can also change the topography of the road to prevent a drift from forming. [N]

NYSDOT has contracted with the State University of New York - Buffalo and Brookhaven National Laboratory to develop a similar software program that will allow roadway design engineers and maintenance engineers to enter readily available or easily obtained information on weather and topography and then determine the best approach to snow drift control at the site - redesigning the highway cross-section, installing snow fences, or planting trees or other vegetation. The ability to look at different solutions makes the software particularly useful for states where the lack of public land and the relatively high population density can make it hard to find suitable locations for snow fences.

Figure 6 : Projected Snow Drift with and without Snow Fence in Place

Projected Snow Drift

with snow fence
From June 1998, FOCUS, http://www.tfhrc.gov/focus/archives/Fcs698/068snow.htm

Mn/DOT Snow Fence Design Module

Mn/DOT funded a team of researchers and practitioners to develop a model to determine proper mitigation strategies, including appropriate living snow fence design. Entitled Implementation of Climatological Summaries for Blowing Snow Control: Design, Training, and Website Development, the project investigated several climatological factors such as snowfall season (onset and end date), snowfall amount and density, and wind frequency distributions.

To check for potential problems when designing a roadway or solve a drifting problem on an existing roadway, two parameters must first be quantified. These are the total seasonal snow transport, and the direction of greatest snow transport. Research results from a previous project provided the necessary climatological data to quantify these parameters on a site-specific basis. The three attributes that are required are: 1) length of snow season, 2) snowfall during the season, and 3) the potential snow relocation coefficient based on topography, wind speed, and vegetative cover. Data were analyzed using a database containing the climatic history of 370 locations, some dating back to the 1850s. With this information, a web-based snow-control design module was developed that allows users to obtain necessary climatological attributes for various road and snow fence designs. The web site is an interactive snow control design tool utilized by design/pre-design Mn/DOT personnel and natural resource managers. With it designers can utilize this site to:

  • Obtain necessary climatological information for GEOPAK,
  • Test for problems on an existing roadway and investigate possible solutions, and
  • Design a living or structural snow fence for a given problem area. The web environment allows the user to select any location in Minnesota and in so doing; necessary climate information will be given.

Plastic Snow Fence Research Results

Research on the configuration of the openings in plastic snow fence by the North Dakota Department of Transportation indicated that the configuration did not have a bearing on the amount of snow that accumulates in front of the fence; however, the Morton County road crew who installed and maintained the fence made the following observations: [N]

  • Plastic fence is easy to handle, not near as bulky as wood fence. A two-person crew can handle the installation.
  • It is critical to have a good installation, solid end posts, and midway supports such as lath. If end posts loosen, the fence will sag and become ineffective.
  • There is considerable variation in the quality of the fence, with some types tearing more easily and some that are more difficult to handle.
  • More maintenance is required with plastic fences than with wood fences.
  • The effectiveness of plastic fence in holding back snow appears to be as good as wood fence.
  • Costs of plastic fence vary considerably. Usually plastic fence is considerably less costly than wood fence; however, a high-quality plastic fence may cost almost as much as wood fence and should have a useful life considerably longer than a wood fence, since wood slats and wire tend to break.

Living Snow Fence

All of the principles pertaining to snow fences apply to vegetative barriers as well, but guidelines for plantings must consider the variability or irregularity of height and porosity, and how these factors change with time. In addition, biological requirements must be considered in the planting and maintenance of living snow fences, as well as ecological factors that affect survival and growth. For these reasons, designing living snow fences requires the knowledge of agronomists, foresters, landscape architects, and engineers. Living snow fences include rows of trees and shrubs that, if planted in the right location, can cause snow to accumulate in a more convenient area and can also improve visibility during and after snowstorms. Considering direct and indirect costs, living snow fences cost about the same as structural fences. [N]

Living Snow Fence Placement and Design

The following guidelines for living snow fence placement and design were developed by Mn/DOT. [N]

  • To improve visibility and/or prevent drift accumulation on highway sections in areas where there is 10,000 feet of "fetch distance" (open distance perpendicular to the centerline), a living snow fence should be planted 250 feet from the centerline. Note that normal rights-of-way are typically 75 - 100 feet from the centerline, but that planting on existing rights-of-way may extend drift formation onto the road surface. In these situations, additional right-of-way should be purchased, or easements obtained, to plant the snow fence. In areas where the "fetch distance" is only a few thousand feet, a living snow fence planted 100 feet from centerline will still be effective.
  • A strip of tall grasses 12 feet wide will actually trap the snow and hold it. Native grasses are an attractive addition to farmsteads and field borders because they remain upright during the winter and provide wildlife with excellent cover for the winter and nesting habitat in the spring.
  • Proper design of a living snow fence involves three key elements: height, density, and length.
  • Height: This affects the snowdrift length and depth. Snow storage capacity increases by more than four times when the height is doubled. Typically, vegetative barriers should be set back from the area to be protected 10 - 15 times the mature height of the vegetation.
  • Density: This affects both windward and leeward snowdrift lengths and heights. The species, number of rows, and plant spacing determine density. Winter density of deciduous trees must also be considered. Density should be uniform with no openings and gaps.
  • Length: This determines the maximum length of the area that can be protected. Less snow is stored at the ends of barriers, so the snow fence must extend 100 feet beyond the area to be protected.
Strategies in the Use of Plant Materials

There are two basic approaches to the use of plant materials to control blowing snow:

  • Snow collection - Trapping incoming blowing snow with rows of trees or shrubs
  • Snow retention - Holding the snow in place with grass, shrubs, or trees. These control measures will be referred to as retention plantings.

The latter strategy is applicable where the source of the blowing snow is confined to the immediate vicinity of the road, such as embankment slopes, medians, and interchange areas.

Selecting Plants for a Living Snow Fence

Trees and shrubs suitable for drift control should have relatively dense foliage that extends to ground level. General recommendations include:

  • Use dense foliage species that are fast growing; resistant to drought, frost, and disease; unpalatable to livestock and wildlife; tolerant of crowding without shedding lower branches; and should have a service life of 30 to 50 years. Secondary considerations include ornamental value and value for cover and food for wildlife. Coniferous species have the advantages of year-round dense foliage and relatively low palatability for wildlife. Deciduous trees and shrubs can also be used, but more rows are generally required and many species are browsed preferentially by livestock and wildlife.
  • Use plants that are adapted to site conditions such as soil pH, soil moisture extremes, and soil texture. County extension services can provide information regarding general conditions, but the advice of a forester or agronomist should be sought for recommended species for climate and soil conditions at specific sites.
  • Avoid self-pruning species.
  • Avoid plants for which a major insect or disease is known to cause problems with establishment and long-term survival. Most plants have characteristics that make them susceptible to one or more problems, such as insects, disease, and storms. Although in most cases pest- and weather-related problems are minor concerns, selecting a variety of plants with similar growth and site requirements can minimize the risk of a single problem destroying the snow fence planting.
  • Shrub rows between the road and tree plantings provide a temporary control until the trees become fully effective.
  • The best in-row spacing for coniferous trees is approximately 2.4 m (8 ft), with rows spaced 2.4 to 3 m apart (8 to 10 ft). Three rows are recommended to reduce the possibility of gaps forming when trees die.

The Minnesota Interagency Living Snow Fence Task Force developed "winning combinations" for snow fences, based on observations made during the winter of 1996 - 1997, site visits, past experience, and recent work understanding snow transport. The required fence height and setback for any of these combinations is based on the principal of snow transport. Design criteria can be obtained from the 1999 publication titled "Catch the Snow with Living Snow Fences," published by Mn/DOT Office of Environmental Services. The five winning combinations for use as a living snow fence are:

  • Twin row tall grass native prairie snow catch
  • Twin shrub row
  • Deciduous tree windbreak
  • Vertical side community shelterbelt
  • Structural snow fence
Partnerships with Farmers to Leave Standing Corn

Iowa DOT is using standing-corn snow fences to save about 75 percent of the cost of erecting snow fences. In several Iowa counties, farmers are paid 50 cents more than market price to leave four to six rows of corn standing in areas where there are major problems with drifting snow on the roadway. This natural snow fence also helps improve visibility during snowstorms. Farmers benefit by a fair price for their corn, which is often picked by nonprofit groups in the spring. If the corn is given away at that time, the farmers may deduct the value of the corn as a charitable donation. [N] [N]

Minnesota DOT will pay $1.50 more than the current bushel price for cornstalks that farmers leave standing in their fields to act as living snow fences. Mn/DOT determined that one 40-foot-wide, quarter-mile-long snow fence is capable of capturing 11,800 tons of snow, minimizing snow and ice on roads and decreasing removal costs. [N]

 

3.10.3 Designing Drainage to Minimize Anti-Icing and Deicing Impacts to Natural Resources
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The main purpose of any road drainage system is to safely convey runoff downstream to either a natural or man-made drainage system. Management measures should be implemented to ensure that this is done with minimal impact to the infiltration characteristics, water quality, erosion potential, and flood risk of the receiving drainage system. Training for drainage designers should include design options for managing the adverse effects of snow and ice control chemicals. Drainage designers need to consider the environmental setting into which their drainage system will be placed. The Transportation Association of Canada's synthesis of best practice for doing so recommends the following: [N]

  • At the onset of any drainage design, sufficient information should be collected to characterize the existing drainage system surrounding and downstream of the roadway.
  • A surface water assessment should be completed to identify all potential impacts to natural features as a result of the roadway. The assessment should include a review of the impacts of salt-laden surface water on potable water taken from groundwater sources, sensitive aquatic habitat, agricultural lands, wetlands, and wildlife. The requirements of the assessment are defined by the policy framework in the area where the drainage design is being completed. Specific site characteristics may require that other features be considered as well. The impact potential identified for all significant features assists in the selection of suitable mitigative measures.

    Oregon DOT recommends review of the following environmentally sensitive areas and natural resources: [N]
    • Spawning streams and those inhabited by protected aquatic species, especially salmon and trout.
    • Those receiving direct runoff from treated roads & highways where there would be less than 100:1 dilution.
    • Those where a large volume of highway runoff can directly reach small, poorly flushed ponds, lakes and wetlands.
    • Those where receiving water temperatures have warmed by the time highway runoff arrives.
    • Those areas where shallow ground water is overlain by very coarse and permeable soils.
    • Drywells, French drains, or similar facilities that allow surface water access to underground aquifers.
  • The relative importance of each feature as defined by low, medium or high potential for impact should be established. Further guidance on considering impacts to various classes of resources is included below. The potential for salt impacted drainage to affect each of these vulnerable areas should be assessed.
Groundwater

The suitability of groundwater for potable use and irrigation can be significantly impaired by the infiltration of salt captured by roadway runoff. For example, the Maine DOT noted that road salt is gradually accumulating in bedrock aquifers, causing some drilled wells to become unusable. The rate at which salt enters aquifers and how much salt is eventually discharged naturally from aquifers is unknown, making prediction of long-term impacts problematic. In 2004, Maine DOT decided to establish two sites where new highway construction is proposed for monitoring well installations over the next five years. [N]

To determine the potential for impact from salt-laden runoff on groundwater, the following questions must be addressed:

  • Are there domestic wells near the roadway?
  • If there are wells, do they draw from a surficial aquifer?
  • Are the surficial soils permeable (sands and loams)?
Aquatic Habitat Impacts

Salt-laden runoff can potentially impact aquatic habitat in two ways: sudden pulses of chlorides during spring runoff, and continuous levels of chloride present in the groundwater discharging to the receiving stream. Although both types of impacts are a concern, the literature generally points to sudden pulses as the greater concern. With either type of impact, the existing literature is not clear on "how much is too much." The following provides a guideline for assessing the potential impact:

  • High: The receiving watercourse has a permanent baseflow, and the catchment area of the road represents more than 10 percent of the catchment area of the stream.
  • Medium: The receiving watercourse has a permanent baseflow, and the catchment area of the road represents less than 10 percent of the catchment area of the stream.
  • Low: All other cases (i.e. receiving watercourses with no permanent baseflow).
Agricultural Land

Salt-laden runoff can impact crops in cases where there is the potential for water to pond on agricultural lands. This situation can arise where there is poor positive drainage or an outlet has been blocked by ice or debris. Guidelines for assessing potential impacts are as follows:

  • High: Agricultural land is adjacent to the road, and off road drainage has a high likelihood of ponding or blockage.
  • Medium: Agricultural land is adjacent to the road, and off road drainage has a low to moderate potential for ponding or blockage.
  • Low: Agricultural land is either outside the road runoff influence zone, or there is no agricultural land adjacent to the road.
Wetlands

Swamps, peat bogs, marshes, and other types of wetlands can be impacted where runoff is directed to natural roadside vegetation features. In these cases the runoff may enter the wetland as sheet flow or via a roadside ditch. With very high and prolonged chloride loading, changes in local plant composition may occur, with the possibility of a reduction in the overall value and diversity of the wetland. Small, perched wetlands that intercept the shallow water table or that are primarily surface water dependant may be most susceptible to chloride loading effects due to their small size and a reduced dilution potential. Large wetlands with extensive catchment areas and high dilution potential are likely more tolerant of chloride loading. Potential impacts may be classified as follows for wetlands located adjacent to the roadway:

  • High: No clear flow path evident through the wetland and/or small perched roadside wetlands present (<5 ha in size).
  • Medium: Poorly defined channel evident through the wetland and/or moderate sized wetland with better dilution potential (5 -20 ha in size).
  • Low: Clearly defined channel evident through the wetland and/or large wetland with good dilution potential (>20 ha in size).
Wildlife

Ponded runoff can serve as a salt source for wildlife. The attraction of the wildlife to the saltwater can be a safety hazard. Potential impacts may be classified as follows:

  • High: Roadway located in an area where large mammals (such as elk, big horned sheep, white-tailed deer and moose) are present and where roadside ponding is a current problem or has a high potential based on design limitations and topography.
  • Medium: Roadway located as above but roadside ponding is not a current problem or has only a moderate potential based on design limitations and topography.
  • Low: Roadway located as above but there is no existing or future roadside ponding problem, or large mammals are limited or absent in the area.

Structural Roadside BMPs to Control Deicing and Anti-Icing Chemical and Abrasive Laden Runoff

The range of potential impacts from salt-laden runoff offers considerable challenges to the designer. There are a number of practices that can aid in the management of runoff, however each practice may mitigate some types of impacts while accentuating others. For example, promoting rapid conveyance of runoff to a receiving watercourse will reduce the potential for impairment of potable groundwater while increasing potential impacts on aquatic environment. Special design modifications to traditional stormwater management measures may be warranted to protect vulnerable areas. Measures to protect salt vulnerable areas may include clay or geosynthetic liners in conveyance ditches and ponds, infiltration ponds, or use of storm sewers to transport drainage past vulnerable areas.

The Transportation Association of Canada (TAC) recommends consideration of eight alternative management practices, which are often used to achieve other drainage objectives and may be used in combination to effectively minimize impacts related to salt rich surface drainage.

  • Records should be kept on the chloride or conductivity levels and snow and ice control events to determine how the levels fluctuate around an event and whether BMPs are having the desired effect. The analyst will want to be able to draw conclusions on whether or not the applications of best salt management practices are having an effect on the chloride levels in the aquatic environment. It will be important to determine whether or not drops in chloride levels can be attributed to improved practices and not just different weather conditions. This will require coordination with Maintenance.

TAC's table below illustrates the merits of each management practice in addressing the potential impacts that can result from salt-laden runoff. Practices which benefit groundwater impacts are typically consistent with those that benefit agriculture, wetlands, and wildlife. However, most of these practices have the potential to negatively impact aquatic resources. Thus, measures should be selected as part of the overall management strategy formulated to achieve overall drainage and stormwater management objectives. In cases where objectives are conflicting, the practitioner must review each site on its own merits and set priorities such that the overall impacts are minimized. In addition to local policy frameworks, design information for these measures can be found in numerous technical documents relating to stormwater management. [N]

Table 9 : BMPs for Minimization of Salt-Related Impacts - Transportation Association of Canada

BMPS - Salt Related
From Transportation Association of Canada, "Syntheses of Best Practices: Road Salt Management."

Table 10 : BMP Characteristics and Impact on Minimization of Salt-Related Impacts - Transportation Assoc. of Canada

BMP Characteristics
From Transportation Association of Canada, "Syntheses of Best Practices: Road Salt Management."

 

3.10.4 Snow Disposal and Snow Storage Site Design
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At high latitudes, snow plowed from streets accumulates rather than melts. As plowed snow accumulates and exceeds available storage space along streets, it is hauled to central storage areas and placed as a compact snowfill. A portion of the applied grit and salt, as well as fugitive pollutants from vehicles, becomes incorporated into hauled snow. Heavy metals, inorganic salts, aromatic hydrocarbons, litter, debris, and suspended solids accumulate on road surfaces along with oil, grease, rust, hydrocarbons, rubber particles, and other solid materials deposited by vehicles. Runoff, snow, and melt water collect these pollutants, along with debris, and chloride, sodium, and calcium from winter road operations. [N] Such contaminants become pollutants when they interfere with the normal life cycle functions of organisms living in or dependent on the water source. [N]

The Alaska Department of Transportation and Public Facilities (ADOT&PF) is synthesizing best management practices (BMPs) for handling and treating the melt water snow storage areas, including performance requirements for runoff treatment in the various water quality management jurisdictions and climatological regions, potentially applicable technologies/BMPs that have been used successfully in other locations and jurisdictions, the applicability of available technologies/BMPs, cost effectiveness of various potentially applicable BMPs, and research and development needs for BMPs. [N] The Municipality of Anchorage (MOA) conducted a four-year study of snow disposal sites from 1998 through 2001, sponsored by the MOA Street Maintenance Department and the ADOT & PF, Central Region Maintenance and Operations that revealed three important factors related to how pollutants are released during melting: initial source of hauled snow, melt processes of stored snowfall, and shape of storage areas and the snowfills). [N] The study concluded that: [N]

  • Chloride can be controlled passively only through detention and dilution.
  • Mobilization of metals and polynuclear aromatic hydrocarbons relates to chloride concentration, but a large fraction can be controlled with particulate capture.
  • Particulate loading in meltwater relates to the shape of the snowfill and the pad on which it is situated and can be controlled by manipulation of these elements.

Control of Chloride through Detention and Dilution

Chloride is not readily treated by simple technologies. Passive (non-chemical) treatment of chloride is best addressed through: [N]

  • Control of street treatment processes (i.e., reducing use of salt).
  • Dilution of early meltwater discharges. The necessity for dilution and the potential for impact to other local resources from elevated chloride requires careful consideration to facility siting.
  • Application of snow disposal site location criteria. Analysis of Anchorage salt application practices suggested that total chloride loading could be reduced by as much as 60 percent through use of heated sand sheds.

Control of Particulates and Subsequent Mobilization of Metals and PAHs

As noted in the Alaska study, mobilization of metals and polynuclear aromatic hydrocarbons (PAHs) relates to chloride concentration, but a large fraction can be controlled with particulate capture. Furthermore, particulate loading in meltwater relates to the shape of the snowfill and the pad on which it is situated and can be controlled by manipulation of these elements. Turbidity of meltwater is a function of meltwater exposure to fine sediment:

Turbidity in snow disposal site flows is generated as meltwater exits and cascades off a snowfill, gathering sediment from the surface of the deflating mass.

Turbidity may be further increased as meltwater crosses a pad surface, particularly if pad surface soils are unprotected, waste soils are exposed, or flow velocities are increased.

Environmental Stewardship Practices in Design and Operation of Snow Storage Sites

The Transportation Association of Canada [N] , the NHDOT [N], and the ADOT&PF [N] have each compiled snow storage guidelines for design and operation, which are combined below.

Needs Assessment
  • Review potential sites considering:
    • Surface water quality and quantity (including potential assimilative capacity).
    • Site hydrogeology.
    • Location of groundwater recharge areas.
    • Location and nature of salt vulnerable areas including wetlands, sensitive vegetation, agricultural areas, drinking water supplies, shallow ponds, etc.
    • Location of sensitive land uses such as residential, institutional and recreational areas.
  • Review public, agency and staff concerns with existing sites and develop a list of potential concerns that should be resolved during the planning and design process.
  • Involve the public and government agencies in the site selection process.
  • The identification of potential temporary, contingency or emergency sites may focus on smaller more remote sites with natural features supporting basic siting criteria such as:
    • Soils with a low permeability
    • Natural slopes with a ponding area
    • Discharge to a high volume surface water receiver or sanitary sewer
Assessment and Evaluation

The assessment and evaluation process is iterative with increasing level of detail being used as sites are narrowed down. Many of the same criteria are used for the evaluation of existing and new snow disposal sites. The following criteria should be considered as part of the assessment and evaluation process.

  • Snow hauling distances
    • Snow hauling routes and site access
    • Past and current site land use
    • Current and future surrounding land use
    • Zoning
    • Size of the site
  • A snow disposal site must have an area sufficient to accommodate:
    • Anticipated volumes of snow
    • Site access/control facility
    • Drive paths for the heavy trucks allowing for simultaneous arrivals and departures
    • Parking and re-fueling area for bulldozers, blowers, etc.
    • Temporary storage for large debris
    • Berms around the perimeter
    • Meltwater collection/retention/settling ponds
    • Maintenance access
    • Monitoring stations/sites
    • Consideration for other uses if included or desirable
  • Sub-surface conditions. Preference should be given to sites with low permeable soils with sufficient bearing capacity to handle year-round operation of heavy equipment.
  • Protection of water quality may be the most important and difficult of issues to address. Map local and site hydrogeology within 300-meter (m) of site. Consideration should be given to:
    • Proximity to drinking and irrigation water sources (avoid possible contamination).
    • Proximity to surface water, downstream effects and the type of aquatic species present (avoid or minimize impacts).
  • Meltwater discharge location. If ultimate discharge is into municipal sanitary system, ensure the treatment system can handle the additional flow and contaminants. When discharging meltwater into a surface water body the receiver must provide enough dilution all year round to protect the aquatic eco system. The potential receiver should be evaluated both on its historical flow rate and volume fluctuations and potential for future fluctuations, particularly lower flow periods. Meltwater should not be discharged to salt vulnerable areas, including ground water recharge areas, and areas over shallow aquifers.
Base Construction
  • A good solid base is required to allow heavy trucks and graders to drive repeatedly over the wet ground without getting stuck or creating deep ruts that could divert or hold meltwater.
  • The base should have low permeability to protect groundwater resources.
  • The base must remain firm enough to support vehicle loads even after the frost has gone out of the ground.
  • The base should slope downwards to the north to take advantage of the sun melting the pile from south to north. The snow on the high (south) end melts first running under or around the piles to the meltwater collection facility. In this way, contaminants (sand, silt, litter, etc) will remain up-stream of the pile and meltwater will not continuously flow across the materials previously released from the pile.
  • The Municipality of Anchorage and the Alaska Department of Transportation and Public Facilities have designed the base with "V" ditches under the pile to channel meltwater to a collection pond to take advantage of the melting process and inherently low-energy environment of a melting snowfall. The V-swale configuration promotes meltwater movement as saturated flow within a snowfill so that particulates are not mobilized during the early and middle stages of melt, providing as much as ten times the particulate control over conventional fl at pad configurations. Flow directed along the trough of the V-swale ensures a single predictable discharge point so that flows can be further managed and directed to minimize erosion of pad and waste soils. The design also limits late-stage sediment mobilization by helping to short-circuit flows to armored channels.

Restriction of off-season pad use will minimize disturbance of pad soils and to allow revegetation. [N]

Siting Criteria
  • Avoid meltwater discharge to potable water aquifers. The snow storage area should be at least 75 feet from any private water supply wells, at least 200 feet from any community water supply wells, and at least 400 feet from any municipal wells. Prohibit snow storage areas in wellhead protection areas.
  • Optimize opportunities for infiltration to shallow nonpotable groundwater systems.
  • Avoid meltwater discharge to ‘closed' lakes and wetlands.
  • Avoid reduction of functionality of receiving wetlands.
  • Avoid meltwater discharge to streams having winter base flows less than 85 L/sec.
  • Optimize opportunities for a site orientation sloping down from south to north.
  • Snow disposal locations should allow melt water to flow at a low velocity to a water body.
  • Disposed snow should be stored near flowing surface waters, but at least 25 feet from the high water mark of the surface water.
  • Locate and operate snow disposal sites to minimize impacts to the natural environment and control nuisance effects, including noise, dust, litter and visual intrusion on adjacent landowners.
Design Criteria
  • A snow handling, storage and disposal design must be practical and must not impose undue maintenance requirements.
  • Drainage designs need to consider runoff and snow melt while snow is in the storage area. If snow is piled over the top of drainage inlets, the inlets will not function. Rain or melting snow runs down the outside of the snow pile to low areas, forming ponds or flowing across the road.
  • Clearly delineate the actual snow disposal area in a manner that is clearly identifiable under adverse winter conditions, to ensure that the snow is placed in the proper location on the site.
  • Construct pad with a single or multiple V-swale configuration (minimum 45 m crest-to-crest swale width, 2 percent sideslope to central trough, and 1 to 2 percent longitudinal slope).
  • Orient V-swale longitudinal axes downhill from south to north.
  • Establish and flag setbacks from swale crests and facility perimeter.
  • Armor swale troughs and crests and all facility drainage channels and containment berms.
  • "Trackwalk" (imprint with crawler tractor treads trafficking directly upslope and downslope) and vegetate all non-armored pad surfaces with a mix resistant to an annual 2 to 5 cm sediment burial.
  • Construct dry detention ponds or other treatment to control chloride and sediment releases.
  • Install flow dispersion and energy dissipation controls at all outfalls to receiving waters.
Drainage and Meltwater Management
  • Manage the discharge of meltwater to comply with local water quality regulations and protect surface and groundwater resources.
  • Site meltwater should be directed away from the snow piles and dumping area to reduce ponding/rutting.
  • Use of setback staking and armored channels (oversized to provide room for icing) to direct and contain pad meltwater flows and limit turbidity.
  • Where local regulations permit dilution to meet regulated contaminant levels, uncontaminated site drainage and precipitation may be directed to the collection pond to provide dilution of the impacted meltwater. Otherwise, uncontaminated drainage should be isolated from the meltwater. The meltwater collection pond should be designed large enough to handle the expected meltwater volume, other site drainage, and the periodic additional load from precipitation events.
  • Incorporating shallow collection reservoirs reduces pad erosion and turbidity by effectively transporting meltwater over significant horizontal distances in a low-turbulence (pooled) environment. The meltwater collection pond should be designed with an impermeable base, a forebay to collect litter and settle coarse sediments and a larger secondary area to settle finer particles. An absorbent boom can be placed in the forebay to capture any oil and grease in the site drainage. The outlet should be controlled to regulate the release to the receiving water body. The point of discharge should be protected to prevent scour. Adequate access to the pond needs to be provided to allow for periodic cleanout of sediments.
  • A silt fence or equivalent barrier should be securely placed between the snow storage area and the high water mark.
  • All required federal, provincial, regional and municipal approvals, permits and licenses will have to be applied for, obtained, and complied with.
  • A baseline condition evaluation (benchmarking) of the site and surrounding areas should be conducted for future monitoring comparisons.
  • Contaminant levels recorded once the site is operational will have to be compared to levels prior to the site opening to give a true indication of any environmental impacts.
  • Test sites and holes drilled to benchmark the site could be made permanent allowing future comparison data to be collected from the same locations.

 

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Continue to Section 3.11 »
Table of Contents
 
Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.1 Beyond Mitigation: Projects to Achieve Environmental Goals
3.2 Context Sensitive Design/Solutions
3.3 Avoiding Impacts to Historic Sites
3.4 Designing to Accommodate Wildlife, Habitat Connectivity, and Safe Crossings
3.5 Culverts and Fish Passage
3.6 Stream Restoration and Bioengineering
3.7 Design Guidance for Stormwater and Erosion & Sedimentation Control
3.8 Drainage Ditches, Berms, Dikes, and Swales
3.9 Design for Sustainable, Low Maintenance Roadsides
3.10 Designing to Reduce Snow, Ice, and Chemical Accumulation
3.11 Designing to Minimize Air Quality Problems
3.12 Design and Specification for Recycling
3.13 Designing to Minimize Noise
3.14 Lighting Control/Minimization
3.15 Design for Sustainability and Energy Conservation
3.16 Safety Rest Areas, Traveler Services, and Parking Area Design
   
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