Erosion prevention practices - temporary seeding and stabilization
This page is under development. We anticipate populating it in autumn, 2016.
Contents
Temporary Seeding and Stabilization
Definition
The MPCA Construction General Permit defines stabilization, stabilized, and stabilize as meaning that “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.
Purpose and Function
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.
Applicability
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.
Site Applicability
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.
Permit Applicability
The MPCA Construction General Permit has several requirements regarding temporary stabilization.
- Part IV.B.2 of the 2013 MPCA Construction Stormwater General Permit states that the permittee(s) “must stabilize all exposed soil areas (including stockpiles). Stabilization must be initiated immediately to limit soil erosion whenever any construction activity has permanently or temporarily ceased on any portion of the site and will not resume for a period exceeding 14 calendar days.” In addition, “(s)tabilization must be completed no later than 14 calendar days after the construction activity in that portion of the site has temporarily or permanently ceased.”
- Near public waters that the Minnesota DNR has promulgated “work in water restrictions” during specified fish spawning time frames, per Part IV.B.2, “all exposed soil areas that are within 200 feet of the water’s edge, and drain to these waters must complete the stabilization activities within 24 hours during the restriction period. Temporary stockpiles without significant silt, clay or organic components (e.g., clean aggregate stockpiles, demolition concrete stockpiles, sand stockpiles) and the constructed base components of roads, parking lots and similar surfaces are exempt from this requirement.”
- Other permit requirements exist during the construction of post-construction/permanent stormwater and temperature control BMPs discharging to special waters and impaired waters. In those cases, Appendix A Section C.1 of the 2013 MPCA Construction Stormwater General Permit requires that “(s)tabilization of all exposed soil areas must be initiated immediately to limit soil erosion but in no case completed later than seven (7) days after the construction activity in that portion of the site has temporarily or permanently ceased.”
- Finally, it shall be noted that stabilization requires more than seed alone. Appendix B Section 26 of the 2013 MPCA Construction Stormwater General Permit defines stabilization 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. Mulch materials must achieve approximately 90 percent ground coverage (typically 2 ton/acre).”
Effectiveness
Temporary seeding and stabilization is effective in reducing soil loss from construction sites once vegetation has become established (Table 1 1).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 achieving similar results. 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.