SEDIMENT BASIN (No.) Code 350

Natural Resources Conservation Service Conservation Practice Standard

I. Definition filter strips, etc., to reduce the amount of sediment flowing into the basins. A basin constructed to collect and store debris or sediment. The basin shall be located to intercept sediment before it enters streams, lakes, and wetlands. For II. Purpose maximum effectiveness, the basin must be located close to the sediment source. To preserve the capacity of reservoirs, lakes, wetlands, ditches, canals, diversions, waterways, and The capacity of the sediment basin shall equal streams; to prevent undesirable deposition on bottom the volume of sediment expected to be trapped at lands and developed areas; to trap sediment the site during the planned life of the basin or the originating from construction sites; and to reduce or improvements it is designed to protect. abate pollution by providing basins for deposition and storage of silt, sand, gravel, stone, agricultural Sediment basins meeting these design criteria are wastes, and other detritus. assumed to have an 80% trapping efficiency.

III. Conditions Where Practice Applies volume = calculated * planned life * SDR * trap efficiency * 23.5 ft3/ton This practice applies where physical conditions or land ownership preclude treatment of a sediment Where: source or where a sediment basin offers the most 3 practical solution to reduce sediment delivery to Volume = cubic feet (ft ) downstream areas. Calculated erosion = sheet and rill, gullies, etc. (Tons / year) Sediment basins having the primary purpose of controlling suspended solids loading and attached SDR= sediment delivery ratio pollutants from runoff with a permanent pool of Trap Efficiency Assumed to be 80% watershall meet the criteria set forth in Wisconsin Department of Natural Resources (DNR) Standard If it is determined that periodic removal of 1001, Wet . sediment will be practicable, the storage capacity may be proportionately reduced. IV. Federal, State, and Local Laws Provisions shall be made for draining sediment Users of this standard should be aware of potentially pools if necessary for safety and vector control. applicable federal, state, and local laws, rules, regulations, or permit requirements governing Appropriate safety measures, such as warning sediment basins. This standard does not contain the signs, rescue facilities, and fencing, shall be text of federal, state, or local laws. provided as necessary to protect the public from floodwater and soft sediment. V. Criteria Sediment storage of the basin shall be a A. General Criteria for Non-Livestock Area minimum of 3 feet deep. Sediment Basins The minimum surface area of the sediment basin, Sediment basins should be used in conjunction measured at the principal spillway elevation, with erosion and practices, such shall be sized based on the texture of the soil as temporary seeding, mulching, diversions, entering the basin and the peak outflow during the 1-year, 24-hour design storm.

Conservation Practice Standards are reviewed periodically and updated if needed. To obtain the current version of this standard, NRCS, WI download it from the electronic Field Office Technical Guide, or contact the NRCS State Office or the Wisconsin Land and Water 8/08 Conservation Association office at (608) 441-2677. 350-2

Sa = 1.2 * (qout / vs) orifice or other device as needed. The top of the perforated riser shall be capped or a trash Where: guard provided to prevent trash from reaching and plugging the orifice. Sa = Minimumm treatment surface area of the sediment basin (square feet) 2. Temporary Sediment Basins

qout = Peak outflow (cubic feet/second) during the 1-year, 24-hour design Temporary sediment basins are used where storm for the principal outlet the basins will be used for periods of 2 years or less. They usually have earthen vs = Particle settling velocity (feet/second) embankments and/or excavated basins, and 1.2 = safety factor may have mechanical spillways, crushed stone or gravel outlets, or other appropriate Table 1 outlets.

Class Vs (ft/sec) Size* Temporary sediment basins having a total 1 .0012 S, LS, SL embankment height of 5 feet or less and 2 .000073 L, SiL, Si, SCL where failure of the embankment or outlet 3 .000012 CL, SiCL, SC, SiC would not cause loss of life or damage to S = Sand Si = Silt C = Clay L = Loam high value property, may be designed with *Based on dominant textural class. an embankment having a minimum top width of 4 feet and side slopes of 2:1 (2 Shape – The length to width ratio of the flow horizontal to 1 vertical) or flatter. path shall be maximized with a goal of 3:1 or greater. The flow path is considered the general The minimum sediment storage capacity of direction of water flow within the basin a temporary sediment basin shall be 0.5 including the treatment surface area and any acre-inches per year from the contributing forebay. drainage area.

The foundation preparation and cutoff, earth Removal – Temporary sediment basins shall embankments, principal spillways, and auxiliary be removed after the contributing drainage spillways shall be according to NRCS Field area has been stabilized. Complete final Office Technical Guide (FOTG), Section IV, grading and restoration according to the site Standards 378, ; or according to the plans. requirements in NRCS Technical Release 60, (TR-60), as appropriate. 3. Livestock Area Sediment Basins

1. Permanent Sediment Basins Sediment basins can be used to trap solids from concentrated livestock areas prior to Permanent sediment basins are used when entering storage, buffer, or filter systems. the basins will be used longer than 2 years. The basin can be either an off-lot basin or an They usually have earthen embankments on-lot basin with additional heavy use and/or excavated basins with mechanical protection for the livestock area. See NRCS spillways. FOTG, Section IV, Standard 561, Heavy Use Area Protection, for surfacing options. Minimum sediment storage capacity shall be 0.3 acre-inches from the contributing The bottom elevation of the sediment basin drainage area. shall be at least 2 feet above bedrock or groundwater. A minimum of 0.3 feet Basins may have a dry or wet sediment pool. freeboard shall be added to the storage Wet sediment pool basins are more effective depth. than dry sediment pool basins in trapping fine sediments. A normally dry sediment The sediment basin discharge shall be stored pool basin shall employ a drawdown device, or treated in accordance with NRCS FOTG, such as a perforated riser or subsurface Section IV, Standards 313, Waste Storage drain, that will drain the pool below the Facility, or 635, Vegetated Treatment Area, principal spillway crest while retaining the as applicable. sediment as much as practicable. The drawdown flow rate shall be regulated by an

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The design loadings and quality of materials 2 years and the drainage areas are less than 1 for wood and concrete walls shall be in acre. Temporary sediment barriers include accordance with the FOTG Standard 313, synthetic fabric silt fences, straw bale barriers, Waste Storage Facility. coarse aggregate barriers, and other appropriate materials. Runoff shall be based on the 25-year, 24- hour duration storm rainfall. The suggested A temporary sediment barrier may be used where runoff curve numbers are 90 for unpaved the minimum barrier height is less than 5 feet, lots and 95 for paved lots. The minimum and where failure of the barrier would not cause runoff curve number for unpaved lots shall loss of life or damage to high-value property, or be 85. significant damage to lower-value property. The barrier shall be adequate to retain the sediment The peak discharge from animal lot areas and handle the 10-year, 24-hour duration storm shall be a minimum of 1010 cubic feet per frequency discharge without failure or significant second per square mile for each inch of erosion for the anticipated life of the barrier. runoff. (NRCS Technical Release 55 [TR- 55], Exhibit 5-II, Tc=0.1 Hours, Travel 1. Straw Bale Sediment Barriers Time=0.0 Hours,

and IA/P =0.10). Straw bale sediment traps should only be used in situations where a life span of less Flood routing of the sediment basin shall than 3 months is required. utilize procedures contained in TR-55, Chapter 6, or NRCS National Engineering Straw bale sediment traps shall be installed Handbook (NEH), Part 650, Engineering on the contour, except that the ends shall be Field Manual, Chapter 11. extended upslope to prevent water from bypassing the ends. The sediment basin shall have sufficient capacity, as a minimum, to store 65 percent The maximum length of uncontrolled slope of the peak inflow rate from a 25-year, 24- upstream from a straw bale hour duration storm for a duration of 15 should be 100 feet. minutes. Any basin outflow shall be disregarded in computing minimum storage. Bales shall be installed so that the bindings are oriented around the bale, not the top and Additional storage capacity, based on bottom of the bales. frequency of cleaning, shall be provided for manure and other solids settled within the The straw bales must be entrenched at least basin. The solids storage volume shall be 4 inches into the ground and anchored with based on the number of livestock, time on two stakes driven through the bale and at the lot (minimum of 25 percent), and seven least 12 inches into the ground. The stakes days between cleanings. The minimum shall be 2" x 2" (nominal) wooden stakes, daily volume of solids per animal for design standard steel fence posts, or ½-inch purposes shall be as specified in Table 2. diameter steel reinforcing bars.

Table 2 Soil shall be compacted against the upstream base of the bales to prevent undermining by Minimum Daily runoff. Gaps between bales must be filled Livestock Volume of Solids per by wedging them full of loose straw or Animal equivalent material to prevent water flow 1,400 lb. dairy cow 1.6 cubic feet between the bales. young dairy stock 1.1 cubic feet/1,000 lbs. 1,000 lb. beef animal 0.9 cubic feet Straw bale sediment traps shall not be used in channels or other areas of concentrated flow. B. General Criteria for Temporary Sediment Barriers Straw bale sediment traps shall be removed once the disturbed area is permanently Temporary sediment barriers are used to trap stabilized and no longer susceptible to sediment from construction or other disturbed erosion. areas where the barriers are needed for less than

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2. Silt Fences Where joints are necessary, each end of the fabric shall be securely fastened to a post. Where a geotextile fabric is used The posts shall then be wrapped around each to trap sediment from disturbed areas, it other to produce a stable, secure joint. shall be installed on the contour, except that the ends shall be extended upslope to Posts prevent water from bypassing the structure. The maximum spacing of posts for non- The maximum length of uncontrolled slope woven silt fence shall be 3 feet and for upstream from the silt fence should be 100 woven fabric, 8 feet. feet. Wood support posts shall be a minimum The geotextile fabric silt fence shall not be length of 4 feet and the full height of the silt used in channels or other areas of fence. The posts shall be a minimum concentrated flow. dimension of 1 ⅛ inches by 1 ⅛ inches air or kiln-dried hickory or oak. The silt fence Geotextile Fabric fabric shall be stapled, using at least 0.5- inch staples, to the upslope side of the posts The geotextile fabric may consist of either in at least three places. woven or non-woven polyester, polypropylene, stabilized nylon, Steel support posts shall be the full height of polyethylene, or polyvinylidene chloride. the silt fence. The posts shall be at least 5 Non-woven fabric may be needle punched, feet long with a strength of 1.33 pounds per heat bonded, resin bonded, or combinations foot and have projections for the attachment thereof. All fabric shall meet the following of fasteners. The silt fence fabric shall be requirements as specified in Table 3. attached in at least three places on the upslope side with 50 pound plastic tie straps A heavy-duty nylon top support cord or or wire fasteners. To prevent damage to the equivalent shall be required. fabric from fastener, the protruding ends shall be pointed away from the fabric. Table 3 All posts shall be driven at least 2 feet into 1 Test Requirement Method Value the ground. Minimum grab tensile ASTM D strength in the machine 120 lbs. Anchor Trench 4632 direction Minimum grab tensile The bottom edge of the silt fence fabric must ASTM D strength in the cross 100 lbs. be anchored by burying in a trench 6 inches 4632 machine direction deep by 4 inches wide on the upslope side of Maximum apparent the posts. The fabric shall be folded to fit ASTM D opening size equivalent No. 30 the trench and backfilled and compacted to 4751 standard sieve the existing ground line. ASTM D Minimum permittivity 0.05 scc-1 4491 Silt fences shall be removed once the .135 scc-1 disturbed area is permanently stabilized and or 10- no longer susceptible to erosion. gallon/min ASTM D ute/square Maximum permittivity 3. Inlet Protection Barriers 4491 foot at 50 mm Inlet protection barriers include, but are not constant limited to, filter fabric barriers, straw bales, head. sandbags, other material filled bags and Minimum ultraviolet socks, and stone weepers. stability (percent of ASTM D 70% strength retained after 500 4355 For temporary barriers that are installed hours of exposure) 1 around storm drain inlets, the perimeter All numerical values represent minimum/maximum length of the barrier must be at least 4 times average roll values. (For example, the average minimum the perimeter of the storm drain inlet. test results on any roll in a lot should meet or exceed the minimum specified values.) Where storm flows could overtop the

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barrier, the top of the barrier needs to be practice, intended life of the components, and criteria level throughout the perimeter length. for design.

Barriers shall be located where a traffic The plan shall include but is not limited to: hazard will not be created and where traffic and construction activities will not destroy A. Inspection of basins immediately after a storm or cause constant need for maintenance of event. Temporary sediment barriers should be the barriers. Barriers shall be located so that inspected after each rainfall event and at least any resulting of storm water will daily during prolonged rainfall. not cause excessive inconvenience or damage to adjacent areas or structures. B. Any part of a sediment basin or barrier that decomposes or becomes ineffective while it is C. Seeding still needed shall be replaced promptly.

All embankments and other disturbed areas, C. Sediment may need to be removed from excluding the permanent storage pond, shall be temporary sediment barriers after each storm seeded in accordance with FOTG Standard 342, event. Deposits must be removed when they Critical Area Planting. reach approximately one-half the height of the barrier. VI. Considerations Sediment in basins shall be removed and the Additional recommendations relating to design that basin restored to its original dimensions when may enhance the use of, or avoid problems with, this the sediment has accumulated to one-half the practice but are not required to ensure its basic designed sediment storage volume. conservation functions are as follows. D. Provisions for proper disposition of sediment A. Effects on the water budget, especially volumes removed from temporary or permanent and rates of runoff, infiltration, evaporation, deep structures. percolation, and groundwater recharge. E. Provisions for removal of temporary sediment B. Drainage area and patterns, and how they may basins or barriers when the sediment source has change due to land use and construction been permanently stabilized and the area activities. reshaped to conform to the existing grade and seeded. C. Potential impacts on and the opportunity to enhance existing streams, lakes, wetlands, IX. References groundwater and wildlife habit. USDA, NRCS, Wisconsin Field Office Technical D. Maximum permitted release rate from the basin Guide, Section IV, Conservation Practice Standards and time limitation for draining the basin without and Specifications. causing secondary problems. USDA, NRCS, National Engineering Handbook, Part E. Means for bypassing excess flows that can't be 650, Engineering Field Handbook. accommodated by the basin. USDA, NRCS, National Engineering Handbook, Part F. Visual quality of onsite and downstream water 651, Agricultural Waste Management Field resources Handbook.

VII. Plans and Specifications USDA, NRCS, Technical Release 55, Urban Hydrology for Small Watersheds. Plans and specifications for installing sediment basins shall be in keeping with this standard and shall describe the requirements for applying the practice to achieve its intended purpose.

VIII. Operation and Maintenance

An Operation and Maintenance Plan shall be developed that is consistent with the purpose of this

NRCS, WI 8/08

Allowance for Settlement

Auxiliary Spillway

Principal Spillway Elevation

Minimum Surface Area

Minimum 3 ft Depth

Structural Height Structural

Natural Ground

Stripping Depth

Sediment Basin Features

NRCS, WI 8/08