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| Soil covers include: 1) sod, 2) sod and turf reinforcement mat combinations (TRMs), or 3) hybrid TRMs such as: High-Strength turf reinforcement mats or geotextile/TRM combinations. Vegetation provides many aesthetic, functional, and synergistic benefits, but is not required for performance. Site goals and environment generally dictate soil cover options. |
Most storm water pipe outlets and parking lot outfalls are good applications for transition mats over sod. Sod provides immediate soil protection with its root mass and top vegetation, and only has to fill-in the voids to be a fully-functioning vegetated BMP. In the event the sod does go dormant, the root mass is there for soil protection.
Sod eliminates any risk of poor seed germination, and in the scope of an erosion control project, is often times not a prohibitive cost, especially if only used under the ScourStop area.
Additional uses include occasional overflow structures and stream bank protection preserving the natural landscape aesthetics. Transition mats over non-rooted sod are proven at velocities greater than 21 feet per second (fps) on a 23% slope.
–See Cohesive Soils Specifications - Page 3or See Non-Cohesive Soils Specifications - Page 3.
Designers must calculate the forces and engineer the appropriate soil cover protection.
Sod eliminates any risk of poor seed germination, and in the scope of an erosion control project, is often times not a prohibitive cost, especially if only used under the ScourStop area.
Additional uses include occasional overflow structures and stream bank protection preserving the natural landscape aesthetics. Transition mats over non-rooted sod are proven at velocities greater than 21 feet per second (fps) on a 23% slope.
–See Cohesive Soils Specifications - Page 3or See Non-Cohesive Soils Specifications - Page 3.
Designers must calculate the forces and engineer the appropriate soil cover protection.
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A sod and TRM combination form a higher level of protection, especially on high volume flow areas, and slopes greater than 10%. This combination provides all of the benefits of sod alone, plus proven shear force resistance greater than 12 pounds per sq. ft. (the root mass continues to provide protection if the sod goes dormant). Appropriate locations would be 36-72+ inch storm water pipes, large culverts, and stream bank restoration where reinforcing all of the vegetation is appropriate.
Downstream of the scour area, this combination practice can be continued to the receiving waters or a stable area. Designers must calculate the flow forces and engineer appropriate soil cover protection.
Downstream of the scour area, this combination practice can be continued to the receiving waters or a stable area. Designers must calculate the flow forces and engineer appropriate soil cover protection.
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The unvegetated flow-ratings for TRMs are fairly low. Maximum flows should be less than 3 feet per second and the covered area fairly level both laterally and longitudinally to minimize concentrated erosive forces. Composite TRMs have shown better initial soil protection, but should only be utilized where vegetation is likely within the mats biodegradable life.
A rural culvert outlet might be an appropriate application, or erosion protection at a temporary construction outlet. Maximum pipe size would generally be 24 inches for an open-weave TRM, and up to 48 inches for a high-performance composite TRM. Stacking transition mats at the immediate scour area has shown to increase performance.
Downstream of the scour area, this soil cover practice can be continued to the receiving waters or a stable area. Designers must calculate the flow forces and engineer appropriate soil cover protection.
A rural culvert outlet might be an appropriate application, or erosion protection at a temporary construction outlet. Maximum pipe size would generally be 24 inches for an open-weave TRM, and up to 48 inches for a high-performance composite TRM. Stacking transition mats at the immediate scour area has shown to increase performance.
Downstream of the scour area, this soil cover practice can be continued to the receiving waters or a stable area. Designers must calculate the flow forces and engineer appropriate soil cover protection.
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Over bare-soil, HS-TRMs provide great mechanical protection, but soil can move under them with significant flows from above, posing some risk of erosion. A 3-4 oz. geotextile under the HS-TRM may be appropriate to improve the soil retention and soil protection properties of an installation, and still allow for soil-filling and vegetative growth from above.
Soil-filling, recommended by the manufacturer, could also come from a true compost material, as well as a properly-applied, full-rate mechanically bonded fiber-matrix hydromulch (MBFM) with the seed mixed-in.
With the geotextile under the HS-TRM, the mat system can collect small gravel and sediment in the voids, appear naturally stabilized, and possibly vegetate naturally over time, while offering long term protection. This installation generally applies to highway construction, continuous low-volume flows like a stream, and semi-arid conditions where healthy vegetation may be a challenge.
Downstream of the scour area, this combination practice can be continued to the receiving waters or a stable area. Designers must calculate the flow forces and engineer appropriate soil cover protection.
Soil-filling, recommended by the manufacturer, could also come from a true compost material, as well as a properly-applied, full-rate mechanically bonded fiber-matrix hydromulch (MBFM) with the seed mixed-in.
With the geotextile under the HS-TRM, the mat system can collect small gravel and sediment in the voids, appear naturally stabilized, and possibly vegetate naturally over time, while offering long term protection. This installation generally applies to highway construction, continuous low-volume flows like a stream, and semi-arid conditions where healthy vegetation may be a challenge.
Downstream of the scour area, this combination practice can be continued to the receiving waters or a stable area. Designers must calculate the flow forces and engineer appropriate soil cover protection.
The ScourStop™ application over a geotextile / TRM combination has shown performance to at least 21 fps on a 23% slope. In a stream bed or shoreline application where vegetation is unlikely, use a heavier 10-12 oz. geotextile for soil retention and soil protection under the transition mats. On non-cohesive soils, the apparent opening size (AOS) of the geotextile must match the soil particle size, to allow for proper ‘back-and-forth flow’ of wave action water pressures. |
