|3.10. Designing to Reduce Snow, Ice, and Chemical
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:
Example 8 : Factors
to Consider in Roadway and Bridge Planning Design to Minimize Snow Accumulation
& Salt Usage
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.
- 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.
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
- 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 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
- 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
Flatten upwind backslope (ideally 7:1 or flatter ) to minimize drifted accumulations
- 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
- 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.
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
- 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
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.
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
- 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
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]
|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.
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
- 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.
Mn/DOT Snow Fence Design Module
Figure 6 : Projected Snow Drift with and without Snow Fence in Place
From June 1998, FOCUS, http://www.tfhrc.gov/focus/archives/Fcs698/068snow.htm
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
- Obtain necessary climatological information for GEOPAK,
- Test for problems on an existing roadway and investigate possible solutions,
- 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
- 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]
Strategies in the Use of Plant Materials
- 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,
- 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
- 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.
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
- 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
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
Partnerships with Farmers to Leave Standing Corn
- Twin row tall grass native prairie snow catch
- Twin shrub row
- Deciduous tree windbreak
- Vertical side community shelterbelt
- Structural snow fence
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
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:
- 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
- Those areas where shallow ground water is overlain by very coarse and permeable
- 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.
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:
Aquatic Habitat Impacts
- 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)?
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
- 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).
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.
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).
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
- 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.
Table 9 : BMPs for Minimization of Salt-Related
Impacts - Transportation Association of Canada
From Transportation Association of Canada, "Syntheses of Best Practices: Road
Table 10 : BMP Characteristics and Impact
on Minimization of Salt-Related Impacts - Transportation Assoc. of Canada
From Transportation Association of Canada, "Syntheses of Best Practices: Road
|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
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
Assessment and Evaluation
- 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
- 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
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
- 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.
- 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
- 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.
Drainage and Meltwater Management
- 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
- 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
- "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
- Install flow dispersion and energy dissipation controls at all outfalls to receiving
- 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
- 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 »