Filter Berm
Description
A filter berm is a temporary ridge constructed of loose gravel, stone, or crushed rock. It slows and filters flow, diverting it from an exposed traffic area. It is used to retain sediment from traffic areas.
Where Practice Applies
Where a temporary measure is needed to retain sediment from rights-of-way or in traffic areas on construction sites.
Advantages
- This is an efficient method of sediment removal which reduces the speed of runoff flow.
Disadvantages/Problems
- A gravel filter berm is more expensive to install than other practices which use materials found on-site.
- Has a limited life span.
- Can be difficult to maintain because of clogging from mud and soil on vehicle tires.
Design Criteria
Berm material should be 3⁄4 inch to 3 inches in size, washed, well-graded gravel or crushed rock with less than 5 percent fines.
Spacing of berms
- Every 300 feet on slopes less than 5 percent.
- Every 200 feet on slopes between 5 and 10 percent.
- Every 100 feet on slopes greater than 10 percent.
Berm dimensions
- 1-foot high with 3:1 side slopes.
- 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design storm.
Maintenance
- Filter berms should be inspected regularly after each rainfall, or if damaged by construction traffic. All needed repairs should be performed immediately.
- Accumulated sediment should be removed and properly disposed of and the filter material replaced, as necessary.
References
U.S. Environmental Protection Agency, Storm Water Management For Construction Activities, EPA-832-R-92-005, Washington, DC, September, 1992.
Washington State Department of Ecology, Stormwater Management for the Puget Sound Basin, Olympia, WA, February, 1992.