SE-6 GRAVEL BAG BERM. Objectives. Potential Alternatives

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1 Objectives Erosion Control - EC Sediment Control - SE Tracking Control - TC Wind Erosion Control - WE Non-Storm Water Management - NS Materials and Waste Management - WM DESCRIPTION AND PURPOSE A gravel bag berm is made of rock 0.75 to 3 in. in diameter and placed along a level contour where sheet flow may be detained and ponded, promoting sedimentation. Gravel bag filters may be used for sedimentation trapping and velocity reduction. See SE-4, Check Dam, for more information. Gravel bags can be used where flows are moderately concentrated, such as ditches, swales, and storm drain inlets (SE-10, Storm Drain Inlet Protection) to divert and/or detain flows. A gravel berm consists of a single row of gravel bags that are installed end-to-end to form a barrier across a slope to intercept runoff, reduce runoff velocity, release runoff as sheet flow, and provide some sediment removal. APPROPRIATE APPLICATIONS Rock Filter A rock filter consists of open graded rock installed at the toe of a slope, along the perimeter of a developing or disturbed area, and as a check dam across construction roads. Their purpose is to intercept sediment laden runoff from disturbed areas of the site, allow the runoff to pond, promote sedimentation behind the filter, and slowly release the water as sheet flow. Legend Removal Effectiveness Unknown Low Medium High Targeted Constituents Sediment Nutrients Trash Metals Bacteria Oil and Grease Organics Potential Alternatives Click here to enter text Rock filters are appropriate where a temporary measure is needed to prevent sediments from entering right-of-ways of traffic areas such as near the toe of slopes, incorporated into temporary stabilized construction entrances/ exits (TC-1), or at other locations along the construction site perimeter. Rock filters may also be used as check dams across one or more lanes of construction traffic temporary roads or unsurfaced rights of way subject to construction traffic. Advantages of the rock filters are that they may be less costly than other temporary barriers, and are relatively efficient at sediment removal. CONSTRUCTION HANDBOOK OCTOBER OF 5

2 Suitable applications include As check dams across mildly sloped construction roads GRAVEL BAG BERM Below the toe of slopes and erodible slopes Along the perimeter of a site Along streams and channels Down slope of exposed soil areas Around temporary spoil areas Around stockpiles Below other small cleared areas At sediment traps at culvert/pipe outlets Along the face and at grade breaks of exposed and erodible slopes to shorten slope length and spread runoff as sheet flow Across channels to serve as a barrier for utility trenches or provide a temporary channel crossing for construction equipment, to reduce stream impacts Parallel to a roadway to keep sediment off paved areas At the top of slopes to divert roadway runoff away from disturbed slopes To divert or direct flow or create a temporary sediment basin During construction activities in stream beds when the contributing drainage area is less than 5 acres When extended construction period limits the use of either silt fences or straw bale barriers When site conditions or construction sequencing require adjustments or relocation of the barrier to meet changing field conditions and needs during construction Slope inclination between 20:1 and 2:1: Gravel bags should be placed on slopes 100 ft and greater at intervals of no greater than 50 ft Slope inclination 2:1 and greater: Gravel bags should be placed on slopes 50 ft and greater at intervals no greater than 25 ft This BMP may be implemented on a project-by-project basis with other BMPs LIMITATIONS Gravel berms may be difficult to remove. Removal problems limit their usefulness in landscaped areas. Not appropriate for drainage areas greater than 5 acres. Runoff will pond upstream of the filter, possibly causing flooding if sufficient space does not exist. Although this BMP will remove some sediment, it is not to be used in place of a linear sediment barrier (i.e., a silt fence, sandbag barrier, or straw bale barrier). Degraded gravel bags may rupture when removed, spilling contents. Installation can be labor intensive. 2 OF 5 OCTOBER 2002 CONSTRUCTION HANDBOOK

3 Limited durability for long-term projects. When used to detain concentrated flows, maintenance requirements increase. IMPLEMENTATION Planning: Gravel filters should be placed along a level contour to intercept sheet flow. Allow ample room for ponding, sedimentation, and access by sediment removal equipment between the berm and the toes of slopes. Flow through the filter should occur as sheet flow in an undisturbed or stabilized area. Installation in streambeds requires large rock, stacking of woven wire sheathing, and daily inspection. Use principally in areas where sheet or rill flow occurs. For rock filter, use larger rock and place in a stacked, woven wire sheathing, if placed where concentrated flows occur. Install along a level contour. Leave area behind berm where runoff can pond and sediment can settle. Drainage area should not exceed 5 acres. Materials Bag Material: Bags should be woven polypropylene, polyethylene or polyamide fabric or burlap, minimum unit weight of four ounces per square yard, Mullen burst strength exceeding 300 lb/in 2 in conformance with the requirements in ASTM designation D3786, and ultraviolet stability exceeding 70% in conformance with the requirements in ASTM designation D4355. Bag Size: Each gravel-filled bag should have a length of 18 in., width of 12 in., thickness of 3 in., and mass of approximately 33 lbs. Bag dimensions are nominal, and may vary based on locally available materials. Fill Material: Fill material should be 0.5 to 1 in. Class 2 aggregate base, clean and free from clay and deleterious material. Design & Sizing Criteria: The following design criteria are commonly used to construct filters: In Non-Traffic Areas: - Maximum flow through rate per square foot of filter=60 gpm - Height = 18 in. minimum - Top width = 24 in. minimum - Side slopes = 2:1 or flatter - Woven wire sheathing (poultry netting) is recommended in areas of concentrated flow. The wire should be 1-inch diameter hexagonal mesh, galvanized 20 gauge. - Build the filter along on a level contour. - Rock: 0.75 to 3 in. open graded for sheet flow, 3 to 5 in. open graded for concentrated flow. CONSTRUCTION HANDBOOK OCTOBER OF 5

4 GRAVEL BAG BERM In Construction Traffic Areas: - Height = 12 in. maximum - Provide multiple filters in series, spaced as shown. 1. Every 300 ft on slopes less than 5% 2. Every 200 f. on slopes 5 to 10% 3. Every 100 ft on slopes greater than 10% When used as a linear control for sediment removal: - Install along a level contour. - Turn ends of gravel bag row up slope to prevent flow around the ends. - Generally, gravel bag barriers should be used in conjunction with temporary soil stabilization controls up slope to provide effective control. When used for concentrated flows: - Stack gravel bags to required height using a pyramid approach. - Upper rows of gravel bags should overlap joints in lower rows. Construct gravel bag barriers with a setback of at least 3 ft from the toe of a slope. Where it is determined to be not practicable due to specific site conditions, the gravel bag barrier may be constructed at the toe of the slope but should be constructed as far from the toe of the slope as practicable. COSTS Gravel filter: Expensive, since off-site materials, hand construction, and demolition/removal are usually required INSPECTION AND MAINTENANCE Inspect gravel bag berms before and after each rainfall event and weekly throughout the rainy season. Reshape or replace gravel bags as needed. Repair washouts or other damage as needed. Inspect gravel bag berms for sediment accumulations and remove sediment when accumulation reaches one-third of the berm height. Removed sediment should be incorporated in the project or disposed of. Remove gravel bag berms when no longer needed. Remove sediment accumulation and clean, regrade, and stabilize the area. Removed sediment should be incorporated in the project or disposed of. REFERENCES Best Management Practices and Erosion Control Manual for Construction Sites, Flood Control District of Maricopa County, Arizona, September Handbook of Steel Drainage and Highway Construction, American Iron and Steel Institute, Storm Water Management Water for the Puget Sound Basin, Washington State Department of Ecology, the Technical Manual February 1992, Publication # OF 5 OCTOBER 2002 CONSTRUCTION HANDBOOK

5 Storm Water Pollution Plan Handbook, First Edition, State of California, Department of Transportation Division of New Technology, Materials and Research, October 1992 CONSTRUCTION HANDBOOK OCTOBER OF 5