The Construction General Permit defines stabilization, stabilized, and stabilize as the exposed ground surface has been covered by appropriate materials such as mulch, staked sod, riprap, erosion control blanket, mats or other material that prevents erosion from occurring. Grass, agricultural crop or other seeding alone is not stabilization.
Stabilization includes a wide range of erosion prevention practices that cover exposed soil such as the use of straw, mulch, erosion control blankets, plastic sheeting or tarpaulins. Temporary seeding is a soil stabilization practice involving the establishment of temporary vegetative cover to reduce erosion on construction sites that have disturbed areas that are temporarily idle (i.e., where no soil disturbing activities occur on that portion of the site for 14 or more consecutive days). Erosion prevention practices like stabilization are generally less costly and more effective than sediment control measures, which involve settling or filtering mobilized soil particles before they are transported by runoff to surface waters.
Temporary seeding and stabilization are intended to counteract the erosive influences of rainfall, rain and snowmelt runoff, and wind on bare soil. Stabilization prevents the mobilization and subsequent transport of soil particles by preventing erosion. Stabilization practices, which mostly include temporary vegetated cover and the application of a mulch, blanket, mat, or other cover on bare soil, is the easiest, cheapest, and most effective approach for addressing sediment loss (muddy runoff and dust) from construction sites. Since temporary seeding is only effective for erosion control once vegetation has established, mulch or other temporary cover is needed to protect seeded areas until vegetation emerges. A good stand of vegetation will protect soil from erosion by raindrop impact and help slow runoff to prevent rill erosion. The vegetation can also act as a filter, trapping coarse sediment particles carried by runoff.
Temporary seeding and stabilization apply to areas of construction sites where soil-disturbing activities have temporarily ceased, and/or immediate measures are needed to prevent erosion and sediment runoff at its source during anticipated rainfall or snowmelt events. Note: Temporary seeding information is presented in this subsection; information on other approaches for temporary stabilization (e.g., blankets, mats, mulches, hydraulically applied products, etc.) can be found in other subsections.
Construction sites often have areas where soil disturbing activities such as clearing, grading, or cut/fill work has stopped for a period of time. Bare areas that are not actively under construction need some type of temporary cover to prevent or minimize erosion in the event of rainfall or snowmelt. Applicable areas include topsoil stockpiles, rough graded areas, sediment basin dikes, ditches, temporary earthen structures, and graded areas undergoing settlement.
The MPCA Construction General Permit has several requirements regarding temporary stabilization. See Section 8.
Temporary seeding and stabilization is effective in reducing soil loss from construction sites once vegetation has become established. As the following table shows, vegetative cover can reduce erosion by up to 99 percent with the application of mulch at the MPCA recommended rate of two tons per acre. Because seeding is only effective after plants have emerged, the application of straw mulch or other cover is required at the time of seeding. Erosion prevention practices such as seeding and mulching are generally more effective and less expensive than sediment control practices.
Bare soil cover types and percent reduction of soil loss. The C factor, used to determine the relative effectiveness of soil and crop management systems in terms of preventing soil loss, is a ratio comparing the soil loss from land under a specific crop and management system to the corresponding loss from continuously fallow and tilled land. Source: Northwest California Resource Conservation and Development District 2016.
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|Vegetative Cover||C factor||Percent reduction of soil loss|
|None (fallow ground)||1.0||0|
|Native vegetation (undisturbed)||0.01||99|
|Temporary tyegrass, 99% (perennial)||0.05||95|
|Temporary ryegrass, 90% (annuals)||0.1||90|
|Permanent seedings (90%)||0.01||99|
|Sod (laid immediately)||0.01||99|
|Mulching (for slopes 2:1 or less)|
|Hay (0.5 tons/acre)||0.25||75|
|Hay (1.0 tons/acre)||0.13||87|
|Hay (1.5 tons/acre)||0.07||93|
|Hay (2.0 tons/acre)||0.02||98|
|Wood chips (6 tons/acre)||0.06||94|
|Wood cellulose (1.75 tons per acre)X||0.10||90|
|Competent gravel layer||0.05||95|
|Rolled erosion control fabrics||(for slope greater than 2:1)||Variable C value by type|
The following table summarizes expected performance for an array of typical water quantity and quality target constituents for temporary seeding and stabilization practices. Once established, a good stand of vegetation will protect soil from erosion by raindrop impact and help slow runoff to prevent rill erosion. The vegetation can also act as a filter, trapping coarse sediment particles (and associated pollutants, including nutrients and some heavy metals) carried by runoff.
Expected performance for temporary seeding and stabilization practices
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|Flow attenuation||Little or no design benefit|
|Runoff volume reduction||Secondary design benefit|
|Soil erosion||Primary design benefit|
|Sediment control||Secondary design benefit|
|Nutrient loading||Primary design benefit|
|Total suspended solids||Primary design benefit|
|Total phosphorus||Primary design benefit|
|Heavy metals||Secondary design benefit|
|Floatables||Little or no design benefit|
|Oil and grease||Little or no design benefit|
Erosion prevention through soil stabilization is always preferred over sediment control, due to cost and overall effectiveness considerations. However, because of the nature of the work, erosion prevention is not always feasible on active construction sites. When a disturbed area will be inactive for a prolonged period, erosion prevention measures are typically required. Areas left undisturbed over the winter should also be temporarily seeded and stabilized.
Temporary seeding is an effective erosion prevention practice that primarily uses the quick emergence of annual seedlings to stabilize bare soil surfaces. As such, proper seedbed preparation and the use of quality seed are important for good germination and growth. A poor stand (less than 50 percent cover) will not provide adequate erosion prevention.
A key planning objective involves the minimization of bare soil footprints at the site, followed by the immediate stabilization of inactive areas through temporary seeding or other measures until the next phase of construction begins. Planning and staging projects in a manner that minimizes the extent and duration of soil disturbance helps to reduce both erosion and sediment loss. In practice, this often means scheduling operations to complete clearing, grading, and cut/fill operations in a phased manner, so that disturbed areas can be stabilized (either temporarily or permanently) as the project proceeds. Planning approach examples include the following.
Outside contractors are not typically required for temporary seeding and stabilization. Keeping the specified seed, straw mulch, rolled erosion control products, and other materials on hand ensures that temporary seeding is implemented timely and efficiently. High priority areas for immediate stabilization include areas within 100 feet of a lake, river, stream, or wetland; slopes steeper than 4H:1V; and ditches and channels within 200 feet of a waterbody or property line.
The current list of MnDOT certified/approved vendors for seed are available on MnDOT's website.
Key design parameters for temporary seeding include: 1) the desired length of time for stabilization; 2) the appropriate type of seed or seed mix; 3) the rate of seed application; 4) the time of year in which the seed is planted; and 5) the type of mulch, blanket, or other material used to cover the site and support the emergent vegetation. Additional design considerations include the following.
Seed mixture selection and other information for various construction site stabilization periods
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|Seed/Mixture Name and Planting Season||MnDOT Mixture #||Common Name||Scientific Name||Rate (lb/acre)||% of Mix (by weight)|
|Oats One Year Cover Crop May 1 – August 1||21-111||Oats||Avena sativa||100.00||100.00|
|Winter Wheat One Year Cover Crop August 1 – October 1||21-112||Winter Wheat||Triticum aestivum||100.00||100.00|
|Soil Building One Year Cover Crop May 1 – August 1||21-113||Field Pea||Pisum sativum||50.00||45.46|
|One to Two Year Stabilization April 1 – July 20 July 20 – October 20||22-111||Slender Wheatgrass||Elymus trachycaulus||9.00||29.50|
|Perennial Ryegrass||Lolium perenne||4.50||14.76|
|Red Clover||Trifolium pratense||8.50||27.88|
|Two to Five Year Stabilization April 1 – July 20 July 20 – October 20||22-112||Perennial Ryegrass||Lolium perenne||13.50||33.75|
|Smooth Brome||Bromus inermis||6.00||14.99|
|Slender Wheatgrass||Elymus trachycaulus||2.00||5.01|
|Big Bluestem||Andropogon gerardii||0.50||1.25|
|Red Clover||Trifolium pratense||5.50||13.74|
|Alsike Clover||Trifolium hybridum||3.50||8.75|
|American Vetch||Vicia americana||0.50||1.26|
Summary of seeding methods and related information for temporary stabilization
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|Method||Site Applications||Site Preparation||Equipment||Mulch Type|
|Drop seeding||Prepared seed beds||Loosen topsoil to a depth of at least 3 inches; leave rough||Drop seeder, followed by cultipacker||Punched-in straw; erosion blanket|
|Broadcast seeding||Prepared seed beds||Loosen topsoil to a depth of at least 3 inches; leave rough||Mechanical cyclone attachment or hand seeder||Punched-in straw; erosion blanket|
|Hydroseeding||Steep slopes and other inaccessible areas; wetland and pond edges||Loosen topsoil to a depth of at least 3 inches; leave rough; avoid hot and dry conditions||Hydroseeder with fan-type nozzle; 500 gallons of water per acre||Bonded fiber matrix; cellulose hydromulch; punched-in straw|
|Inter-seeding||Poorly / sparsely vegetated areas; areas of poor past seeding/germination||Mow existing vegetation; kill broadleaf weeds||Inter-seeding drill with trash ripper, followed by cultipacker||Not required, but recommended for steeper slopes|
MnDOT Specification 2575.3 parts A and B (pages 502 to 504) include guidance for temporary seeding, including seeding dates for various MnDOT seed mixtures, site conditions requiring temporary seeding, and application methods. Part K.3, which covers maintenance of seeded areas, states: “Repair damage within the area caused by Contractor operations and within the Contractor‘s control at no expense to the Department. Reseed areas where the original seed has failed to grow, as directed by the Engineer.”
Specification 2575.4 (pages 510, 511) prescribes requirements for measurement of seed and seeding. Seed should meet Specification 3876 (“Seed”; pages 666-669). Table 3876-1 prescribes standard seed mixes and pure live seed (PLS) application rates (lb/acre)
Inspect areas immediately prior to seeding to ensure that the seedbed is properly tilled (i.e., down to at least 3 inches), roughened so that seed can fall into the spaces between the soil particles, and free of large rocks, woody debris, litter, etc. Inspect again immediately after seeding and mulching for proper coverage and cultipacker (or other roller) results. The seedbed should be lightly compacted, to maximize seed-to-soil contact.
After seed emergence, check for vegetation density and note any bare or sparse areas. Monitor vegetation growth during the first two to five weeks, especially during dry conditions. If the seeding fails to grow, it may need to be re-established to provide adequate erosion prevention. Document any areas that need to be inter-seeded or reseeded, and areas where undesirable vegetation is emerging. Noxious weeds may need to be controlled by mowing or spraying.
MnDOT’s workmanship and rework schedule (2016; version under development at the time of manual update) identifies common deficiencies for various types of stabilization BMPs – including seeding – and corrective actions for these deficiencies. Once complete, the full, final version of this table will replace Table 2575-4 in MnDOT Standard Specifications for Construction (2016 edition).
Table 2575-4: Required corrective action
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|Item||Corrective Action Required if:||Corrective action|
Maintain downgradient sediment controls (e.g., silt fence, fiber rolls) until dense vegetation with uniform coverage is established. Irrigate seeded areas with portable, overhead sprinklers if dry conditions hinder germination or early growth. Cover bare or sparse areas with mulch until they can be reseeded or inter-seeded, which should be done at the earliest opportunity. Mow dense stands of undesirable species that shade out planted areas. Hoe or spot spray weeds as needed. During the first year of establishment, do not mow seedlings until after they are at least 6 inches tall while leaving a minimum height of 3 inches.
An example inspection checklist for temporary stabilization practices is shown on the right (Source: Ohio EPA]).
The following table summarizes estimated BMP costs based on MnDOT data summarizing average bid prices for awarded projects in 2014. (See subsequent sections for cost information on related erosion control products to provide protective cover such as mulch, erosion control blankets, etc.).
Average seeding bid prices
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|Bid Item||Item Description||Units||Average Price|
|2575.502/21111||Seed Mixture 21-111||lb||💲1.57|
|2575.502/21112||Seed Mixture 21-112||lb||💲1.89|
|2575.502/21113||Seed Mixture 21-113||lb||💲3.37|
|2575.502/22111||Seed Mixture 22-111||lb||💲2.34|
Except where more stringent requirements are presented in this guidance, BMPs shall comply with MnDOT and other state requirements. Primary design references include:
The following is a list of additional resources that are not specific to Minnesota: