GeneralErosion matting consists of a wide variety of organic or synthetic mats and blankets placed on the soil surface to reduce erosion from a site caused by concentrated runoff and raindrop impact. These devices are anchored to the exposed surface and help hold the soil in place by forcing runoff to pass through the matting, reducing its velocity and its ability to erode the exposed surface.
This practice is often used on sites where the gradient of the slope is such that mulching, by itself, is ineffective. It is implemented on slopes and in conveyance channels after final grading to prevent erosion and promote the establishment of permanent vegetation.
- Effective practice for stabilizing soil
- Reduces flow velocity
- Encourages the establishment of vegetation and suppress weed growth
- May increase infiltration
- Has a limited life span
- Reduced effectiveness with concentrated flows
- Not applicable on sites where the slope is steeper than 2:1
TypesErosion mats and blankets are available commercially in many varieties of materials and life spans and, depending upon the type selected, may be used above or below grade. Traditional mats and blankets are biodegradable and may be composed of straw, wood, coconut fiber, or a combination and are held in place with netting on one or both sides of the mat. Turf-reinforcement mats (TRMs) are permanent devices, constructed from various types of synthetic materials, which are buried below the surface to help stabilize the soil. The life span of these devices will vary depending upon the type of netting and material used. As a result, careful selection is crucial to the practice’s effectiveness. A current listing of approved erosion mats is available from the Wisconsin Department of Transportation's Product Acceptability List.
Application and InstallationErosion mats and blankets should be applied to the site beginning on the upslope edge, following all of the manufacturer’s specifications. The blanket should then be unrolled down the slope in a loose, uniform manner, without stretching the material and avoiding any wrinkles that may appear. This maximizes the effectiveness of the practice by promoting contact between the ground surface and the blanket, thus avoiding the possibility of concentrated flows from developing beneath the surface of the blanket.
Wherever possible, the material should be large enough so that one continuous sheet is applied over the entire channel or slope. Joints, where necessary, should be overlapped and stapled together. Vertical joints should be overlapped 2-4 inches and stapled at least once every 4 feet while horizontal, or end joints, should be overlapped 10 inches or more, with the upslope blanket overlaying the one down slope. Horizontal joints should be stapled together at least once every 12 inches to promote stability. In addition, mats and blankets must be anchored every 4 feet across the entire surface of the practice to ensure that they remain in place, however, they may not be used on sites with slopes steeper than 2:1.
Erosion blankets should be anchored by either hardwood pegs or metal staples. The staples should be 11 gauge or higher and possess a 1-2 inch crown. Staple length, measured from top to bottom after bending, is dependent upon the soil conditions present on site. Staples and stakes must be at least 6-inches long for compacted soils, while loose, sandy soils require a length of 10 inches or more.
Construction and Maintenance
- Erosion mats and blankets should be installed immediately after the site has been graded and seeded
- Installation should follow the manufacturer’s instructions to ensure the effectiveness of the practice
- Erosion mats should be inspected after each rainfall event for damage (evidence of undercutting or rill and gully formation) with all necessary repairs made immediately
- All other maintenance activities should follow the manufacturer’s specifications