Winter construction practices for site stabilization, erosion prevention and sediment control
This section of the manual is being developed
Contents
Winterization planning
Projects that will either extend more than one season or will still be active during the winter months need to take special considerations when planning for winter shutdown or an active winter construction season. A winter construction plan should be developed to specifically address shutdown procedures or active construction plans. Projects that plan to continue construction during the winter seasons should sequence construction events such that areas having high potential for erosion and sedimentation be fully constructed and stabilized prior to the presence of frozen conditions whenever possible.
Winter shutdown
All winter shutdown activities should be performed before frozen conditions are present and must be completed within 14 days following the end of construction for the season. BMPs should not be installed on top of snow when used as part of winter shutdown.
- Seed all proposed vegetated areas prior to October 1st to ensure germination.
- Stabilize all slopes no later than October 15th with either rock, permanent or temporary vegetation, straw mulch secured with netting (slopes less than 15%), erosion control blanket (slopes 15% or greater). Vegetated slopes that have not germinated with at least 70% cover by October 15th should augment with another method in these areas.
- Stabilize all areas of bare soil (not including road, parking and staging areas) with a temporary seed mix or straw mulch crimped into the soil.
- Apply temporary seed or mulch stockpiles of soil materials with hay or straw at twice the normally recommended rate, with a minimum thickness of 3 inches having 80% to 90% cover. A 4-inch layer of erosion control mix may also be used.
- Install all sediment barriers with adequate area to allow access for inspection and maintenance. Install vertical markers every 100 feet to identify their locations during melt conditions to ensure performance.
- All road, parking and staging areas that have not been fully constructed prior to winter shutdown should be stabilized with a minimum of 3 inches of a sand and gravel mix with a gradation such that less than 12% of the sand passes the number 200 sieve.
Winter construction
Construction during the winter months presents many additional challenges that require modifications to traditional construction practices in order to continue with work. Typically, a winter construction plan should be followed once the ground begins to freeze. Frozen ground can cause equipment slippage during operation, make excavations difficult or impossible with the available equipment, and material stockpiles can freeze, which hinders the ability to achieve adequate compaction or uniformly distribute materials. In addition to the information provided below, MnDOT also includes additional resources.
Winter construction plans typically include the following provisions:
- Reset limits of construction for winter work and install BMPs necessary for winter construction prior to the ground freezing and significant snowfall.
- Ensure that 25-foot clear buffers are maintained to be free of obstructions and more than 2 inches of snow around all perimeter controls for maintenance purposes.
- Designate protected snow storage areas and access routes.
- Widen and stabilize access points to the site.
- Stabilize areas where construction traffic is anticipated with stone (10-20 feet wide for vehicles).
As winter construction progresses, there will be additional needs for stabilization, which cannot be addressed with traditional methods.
- Limit snow pack on construction roads to increase frost penetration in areas with frequent vehicle traffic
- When equipment cleaning is required, it should be performed with compressed air instead of water.
- Temporarily stabilize all earth disturbance at the end of each day, unless that area will be worked on the following day and no precipitation within the next 24 hours is forecasted.
Typical temporary winter BMPs
Link to this table
| Sediment barriers | Erosion control (not to be installed on more than 1" of snow) |
|---|---|
| Erosion control mix berms | Straw mulch (blankets, disc or crimp into soil or snow) |
| Continuous contained berms | Erosion control blankets |
| Sand bag berms | Sand or stone on areas to be paved |
Snow management and storage
Prepare a snow management plan for the site to account for adequate storage of cleared snow through the winter and control of meltwater. Snow storage locations should be placed down slope of all disturbed areas, but not located within stormwater treatment BMPs. Snow mixed with significant amounts of soil should be stored in separate locations that are designed to handle larger volumes of sediment. See the management approaches section under [cold climate impact on runoff management] for additional recommendations.
Earthwork
Many earthwork operations can continue through the winter months on frozen soils with specific modifications.
- Frozen topsoil stripping should only be completed by equipment capable of accurately stripping topsoil to the appropriate depths. If topsoil cannot be separated from subsoil without mixing, stripping operations should cease until soil conditions improve. It may be necessary to precede the grader or dozer with a ripper mounted machine to achieve the appropriate depth penetration. Multiple stripping passes are preferred over a single pass to achieve full depth for stripping operations in order to prevent subsoil mixing.
- Minimize the amount of open trench to limit the amount of trench snow to be removed and to minimize freezing of backfill materials.
- Do not backfill trenches with frozen materials. Frozen surface stockpile materials may need to be removed from stockpiles to access materials that are not frozen.
- Do not spread frozen or saturated topsoil.
- If topsoil cannot be properly spread, the finished subgrade work should be significantly roughened and stabilized with straw mulch that is either spread directly on top of the soil and either disced or crimped in, or spread on top of no more than 1” of snow and likewise crimped into the snow. Final restoration can then take place in the spring when soil conditions allow.
Handling frozen and saturated soils
Occasionally, it may be necessary to relocate frozen or saturated soils to continue with construction. Separate storage locations should be identified for storage of frozen soils and snow mixed with soil. During construction, if mid-winter melts occur over frozen soil, the saturated soil may be removed on access drives and stored in these locations. Additionally, during trenching and excavation operations, frozen soil may be removed and stored here as well to access the unfrozen subgrade. Do not fill excavations with frozen or saturated soils.
Shallow drainage paths with a minimum width of 2 feet should be placed within the soil stockpile areas to direct runoff to treatment BMPs for sediment control and prevent mixing with surrounding spring runoff.
Winter maintenance
Regardless of whether or not a construction site has been shut down for the winter, all installed BMPs must be monitored and corrective actions taken as necessary. Gravel, sandbags, erosion blankets, and mulch should be kept on site to address any immediate repair needs. Repairs to BMPs should be made immediately and any accumulated sediment should be remove upon each inspection.
Inactive construction sites:
- BMPs should be inspected periodically during the winter months to ensure their function. Perimeter controls should be inspected at least monthly
- Inspect BMPs within 48 hours of a rain or melt event.
- BMPs should be inspected at least weekly during periods of warm weather, just before and during spring melt.
Active construction sites:
- BMPs should be inspected weekly or within 24 hours of a rain, heavy snow, high wind event, or melt.
- BMPs within unstabilized areas should be inspected at the end of each day.
- Ensure that all areas of disturbed soil are adequately protected ahead of a forecasted melt event.
- Snow should not be piled against silt fence. A 25’ snow-free area should be maintained around all perimeter controls and upgradient of any silt fence.
- Keep all equipment travel areas as free of snow as possible to increase frost penetration.
- Keep drainage structures open. Check for and remove snow and ice dams to ensure function during construction.
Spring thaw conditions
During spring thaw, it may be necessary to suspend construction activities until soils are no longer saturated. Keeping vehicle travel areas free of snow at night and covered with snow during the day can help to maintain frost penetration in the ground. It is extremely important that all BMPs are being actively monitored and promptly maintained during the spring thaw period.
See cold climate impact on runoff management for recommendations for controlling snowmelt runoff.
References
- Alaska Department of Environmental Conservation, 2011. Alaska Storm Water Guide. Alaska Department of Conservation, Division of Water, Anchorage, Alaska.
- Caraco, D. and R. Claytor, 1997. Stormwater BMP Design Supplement for Cold Climates. Center for Watershed Protection, Ellicott City, Maryland.
- New Hampshire Department of Environmental Services, 2008. New Hampshire Stormwater Manual, Volume 3: Erosion and Sediment Controls During Construction. Section 4.3 Winter Weather Stabilization & Construction Practices. New Hampshire Department of Environmental Services, Concord, New Hampshire.
- Minnesota Pollution Control Agency, 2018. Authorization to Discharge Stormwater Associated with Construction Activity Under the National Pollution Discharge Elimination System (NPDES)/State Disposal System (SDS) Program MNR100001. Minnesota Pollution Control Agency, Saint Paul, Minnesota.
- Stenlund, Dwayne, 2015. Winter Stabilization Practices Guidance Document: Conversion from summer to winter & winter construction, Version 2. Minnesota Department of Transportation, Office of Environmental Stewardship, Saint Paul, Minnesota.
- Vermont Department of Environmental Conservation, n.d. Winter Construction and the Vermont Construction General Permit: A Planner’s Guide. Vermont Department of Environmental Conservation, Water Quality Division, Waterbury, Vermont.
- Vermont Department of Environmental Conservation, 2006. The Low Risk Site Handbook for Erosion Prevention and Sediment Control. Vermont Department of Environmental Conservation, Waterbury, Vermont.