L = length of weir (ft)
D = Average Rock Diameter (ft)
Note: For a stone outlet, the length of stone outlet (L) will vary with the depth and slope of stone outlet. For a gabion, the length of flow is fixed to gabion width. A complete discussion of this equation and its proper application can be found in:
C. McIntyre, G. Aron, J. Willenbrock, and M. Deimler. Report No. 10: Analysis of flow through porous media as applied to gabion dams regarding the storage and release of storm water runoff. NAHB/NRC Designated Housing Research Center at Penn State, Department of Civil Engineering; August 1992.
X Definitions
Stabilized (III): Means that all land disturbing construction activities at the construction site have been completed and that a uniform perennial vegetative cover has been established with a density of at least 70% of the cover for the unpaved areas and areas not covered by permanent structures or that employ equivalent stabilization measures.
Temporary (I): An erosion control measure that is in place for the duration of construction or until the site is stabilized.
Seeding For Construction Site Erosion Control
1059 (11/03)
Wisconsin Department of Natural Resources
Conservation Practice Standard
Note: Words in the standard that are shown in italics are described in X. Definitions. The words are italicized the first time they are used.
I. Definition
Planting seed to establish temporary or permanent vegetation for erosion control.
II. Purpose
The purpose of temporary seeding1 is to reduce runoff and erosion until permanent vegetation or other erosion control practices can be established. The purpose of permanent seeding is to permanently stabilize areas of exposed soil.
Ill. Conditions Where Practice Applies
This practice applies to areas of exposed soil where the establishment of vegetation is desired. Temporary seeding applies to disturbed areas that will not be brought to final grade or on which land-disturbing activities will not be performed for a period greater than 30 days, and requires vegetative cover for less than one year. Permanent seeding applies to areas where perennial vegetative cover is needed.
IV. Federal, State and Local Laws
Users of this standard shall be aware of all applicable federal, state and local laws, rules, regulations or permit requirements governing seeding. This standard does not contain the text of federal, state or local laws.
V. Criteria
This section establishes the minimum standards for design, installation and performance requirements.
A. Site and Seedbed Preparation
Site preparation activities shall include:
1. Temporary Seeding
a. Temporary seeding requires a seedbed of loose soil to a minimum depth of 2 inches.
b. Fertilizer application is not generally required for temporary seeding. However, any application of fertilizer or lime shall be based on soil testing results.
c. The soil shall have a pH range of 5.5 to 8.0.
2. Permanent Seeding
a. Topsoil installation shall be completed prior to permanent seeding.
b. Permanent seeding requires a seedbed of loose topsoil to a minimum depth of 4 inches with the ability to support a dense vegetative cover.
c. Application rates of fertilizer or lime shall be based on soil testing results.
d. Prepare a tilled, fine, but firm seedbed. Remove rocks, twigs foreign material and clods over two inches that cannot be broken down.
e. The soil shall have a pH range of 5.5 to 8.0.
B. Seeding
1. Seed Selection
a. Seed mixtures that will produce dense vegetation shall be selected based on soil and site conditions and intended final use. Section IX References, lists sources containing suggested seed mixtures.
b.
All seed shall conform to the requirements of the Wisconsin Statutes and of the Administrative Code Chapter
ATCP 20.01 regarding noxious weed seed content and labeling.
c. Seed mixtures that contain potentially invasive species or species that may be harmful to native plant communities shall be avoided.
d. Seed shall not be used later than one year after the test date that appears on the label.
e. Seed shall be tested for purity, germination and noxious weed seed content and shall meet the minimum purity and germination requirements as prescribed in the current edition of Rules for Testing Seed, published by the Association of Official Seed Analysts.
2. Seed Rates
a. Temporary Seeding (Cover Crop)
Areas needing protection during periods when permanent seeding is not applied shall be seeded with annual species for temporary protection. See Table 1 for seeding rates of commonly used species. The residue from this crop may either be incorporated into the soil during seedbed preparation at the next permanent seeding period or left on the soil surface and the planting made as a no-till seeding.
Table 1
b. Permanent Seeding
Rates shall be based on pounds or ounces of Pure Live Seed (PLS) per acre. Section IX contains some possible reference documents that provide seeding rates. Permanent seeding rates may be increased above the minimum rates shown in the reference documents to address land use and environmental conditions.
If a nurse crop is used in conjunction with permanent seeding, the nurse crop shall not hinder establishment of the permanent vegetation.
A nurse crop shall be applied at 50% its temporary seeding rate when applied with permanent seed.
3. Inoculation
Legume seed shall be inoculated in accordance with the manufacturer's recommendations. Inoculants shall not be mixed with liquid fertilizer.
4. Sowing
Seed grasses and legumes no more than ¼ inch deep. Distribute seed uniformly. Mixtures with low seeding rates require special care in sowing to achieve proper seed distribution.
Seed may be broadcast, drilled, or hydroseeded as appropriate for the site.
Seed when soil temperatures remain consistently above 53° F. Dormant seed when the soil temperature is consistently below 53° F (typically Nov. 1st until snow cover). Seed shall not be applied on top of snow.
VI. Considerations
A. Consider seeding at a lower rate and making two passes to ensure adequate coverage.
B. Compacted soil areas may need special site preparation prior to seeding to mitigate compaction. This may be accomplished by chisel plowing to a depth of 12 inches along the contour after heavy equipment has left the site.
C. Sod may be considered where adequate watering is available.
D.
When working in riparian areas refer to the NRCS Engineering Field Handbook, Chapter
16, Streambank and Shoreline Protection and Chapter
18,
Soil Bioengineering for Upland Slope Protection and Erosion Reduction.
E. A site assessment should be conducted to evaluate soil characteristics, topography, exposure to sunlight, proximity to natural plant communities, proximity to nuisance, noxious and/or invasive species, site history, moisture regime, climatic patterns, soil fertility, and previous herbicide applications.
F. Use introduced species only in places where they will not spread into existing natural areas.
G. Lightly roll or compact the area using suitable equipment when the seedbed is judged to be too loose, or if the seedbed contains clods that might reduce seed germination.
H. See Section IX. References for suggested seed mixes (NRCS, WisDOT, UWEX) or use their equivalent.
I. Turf seedlings should not be mowed until the stand is at least 6 inches tall. Do not mow closer than 3 inches during the first year of establishment.
J. Seeding should not be done when the soil is too wet.
K. Consider watering to help establish the seed. Water application rates shall be controlled to prevent runoff and erosion.
L. Prairie plants may not effectively provide erosion control during their establishment period without a nurse crop.
M. Topsoil originating from agricultural fields may contain residual chemicals. The seedbed should be free of residual herbicide or other contaminants that will prevent establishment and maintenance of vegetation. Testing for soil contaminants may be appropriate if there is doubt concerning the soil's quality.
N. Consider using mulch or a nurse crop if selected species are not intended for quick germination. When mulching refer to WDNR Conservation Practice Standard Mulching for Construction Sites (1058).
VIl. Plans and Specifications
Plans and specifications for seeding shall be in keeping with this standard and shall describe the requirements for applying this practice.
All plans, standard detail drawings, or specifications shall include schedule for installation, inspection, and maintenance. The responsible party shall be identified.
VlIl. Operation and Maintenance
A. During construction areas that have been seeded shall at a minimum be inspected weekly and within 24 hours after every precipitation event that produces 0.5 inches of rain or more during a 24-hour period. Inspect weekly during the growing season until vegetation is densely established or permit expires. Repair and reseed areas that have erosion damage as necessary.
B. Limit vehicle traffic and other forms of compaction in areas that are seeded.
C. A fertilizer program should begin with a soil test. Soil tests provide specific fertilizer recommendations for the site and can help to avoid over-application of fertilizers.
IX. References
A. Seed Selection References
United States Department of Agriculture – Natural Resource Conservation Service Field Office Technical Guide Section IV, Standard 342, Critical Area Planting.
UWEX Publication A3434 Lawn and Establishment & Renovation.
WisDOT, 2003. State of Wisconsin Standard Specifications For Highway and Structure Construction. Section 630, Seeding.
B. General References
Metropolitan Council, 2003. Urban Small Sites Best Management Practice Manual, Chapter
3, Vegetative Methods 3-85 – 3-91. Minneapolis.
The State of Wisconsin list of noxious weeds can be found in Statute 66.0407.
United States Department of Agriculture – Natural Resources Conservation Service. Engineering Field Handbook, Chapters
16 and
18.
