Conditions where practice applies

Filtrexx™ Filter Berms are to be used in any area requiring sediment or erosion control where runoff is in the form of sheet flow or in areas that silt fence is normally considered acceptable. For the purposes of this document, Filtrexx™ Filter Berms and silt fence are considered approved equals. The use of Filtrexx™ Filter Berms apply to areas of high sheet erosion, on steep slopes up to and exceeding a 2:1 slope, around inlets, and in other disturbed areas of construction sites requiring sediment control. Filtrexx™ Filter Berms may also be used in sensitive environmental areas, where migration of aquatic life, including turtles, salamanders and other aquatic life is impeded by the use of silt fence.

Planning Considerations

Filtrexx™ Filter Berms control erosion by trapping sediment and slowing water that filters through the Filtrexx™ Filter Berms. This will create temporary ponding during heavy rains. It is possible to drive over Filtrexx™ Filter Berms during construction, but these areas should be immediately repaired with a rake or shovel. Continued heavy construction traffic will reduce the effectiveness of the Berms.

Design Criteria for Filtrexx™ Filter Berms:

The sedimentation removal process associated with filter berms involves both filtering and deposition from settling. This is different than other methods using only ponding for deposition of sediment. Ponding occurs when water flowing to and through the filter berm accumulates faster than it can flow through the berm. Typically, berms can handle the same water flow or slightly more than silt fence. However, installation technique is especially important for them to work effectively.

For most applications, it is important to maintain a 2:1 base to height ratio for the berms to be dependably stable.

Level Contour:

Place berms on level contours to assist in dissipating flow into sheet flow rather than concentrated flows. Do not construct berms, which concentrate runoff or channel water. Sheet flow of water should be perpendicular to the berm at impact and relatively un-concentrated.

Flat Slopes:

When possible, place berms at a 5’{ 1.5m} or greater distance away from the toe of the slopes in order for the water coming from the slopes to maximize space available for sediment deposit (see fig. 4.5). When this 5’{1.5m} distance is not available due to construction restrictions, a second berm may be required (see drainage area chart below).

Flow around ends:

In order to prevent water flowing around the ends of berms, the ends of the berm must be constructed pointing upslope so the ends are at a higher elevation.

Vegetation:

For permanent areas, seeded berms allow vegetation to be established directly on the berm and immediately in front and back of the berm at a distance of 5 feet{1.5m}. Vegetation on and around the berms will assist in slowing down water for filtration. The option of adding vegetation will be at the discretion of the Engineer. No other soil amendments or fertilizer are required for vegetation establishment.

Drainage area:

Compost Filter Berm Maximum Drainage Area

Based on Slope and Slope Length

Slope Length (linear feet) Berm Size Required Slope {linear meter} (Height x width)

0%-2% Flatter than 50:1 250 {76.2m.} 1 ft. x 2 ft. {.30 x .60m} 2%-10% 50:1-10:1 125 {38.1m.} 1 ft. x 2 ft. {.30 x .60m} 10%-20% 10:1-5:1 100 {30.48m.} 1 ft. x 2 ft. {.30 x .60m} 20%-33% 3:1-2:1 50 {15.24m.} 1.3 ft. x 2.6 ft{.40 x .80m} >50% >2:1 25 {7.62m.} 1.5 ft. x 3 ft.{.46 x .9m}

*Independent research indicates that Filter Berms are acceptable alternates to silt fence

Dispersing flow:

Sheet flow and runoff should not exceed height of berm capacity in most storm events. If overflow of the berm is a possibility, larger berms should be constructed, or other possible sediment control tools may be used. Alternatively, a second berm may be constructed or used in combination with compost blankets to prevent sediment from moving.

Maintenance Requirements:

Filtrexx™ Filter Berms should be regularly inspected to make sure they hold their shape and are producing adequate flow through. If ponding becomes excessive, berms should be dispersed and reconstructed. For purposes of long-term sediment control objectives, berms can be seeded at the time of installation to create an additional vegetative filtering component.

When construction is completed on site, the berms may be dispersed with a loader, rake, bulldozer or other device to be incorporated in the soil or left on top of the soil for final seeding to occur. No other disposal is required.

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