1.40 BMP C235 - Wattles
Wattles are temporary erosion and sediment control barriers consisting of straw, compost or other material that is wrapped in netting made of natural plant fiber or similar encasing material. They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sediment.
Wattles shall consist of cylinders of plant material such as weed-free straw, coir, wood chips, excelsior, or wood fiber or shavings encased within netting made of natural plant fibers unaltered by synthetic materials.
In disturbed areas that require immediate erosion protection.
On exposed soils during the period of short construction delays, or over winter months.
On slopes requiring stabilization until permanent vegetation can be established.
The material used dictates the effectiveness period of the wattle. Generally, wattles are effective for one to two seasons.
Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water from passing between them.
See Figure 3 - 25: Straw Wattles for typical construction details.
Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length.
Install wattles perpendicular to the flow direction and parallel to the slope contour.
Place wattles in shallow trenches, staked along the contour of disturbed or newly constructed slopes. Dig narrow trenches across the slope (on contour) to a depth of 3 to 5 inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, dig the trenches to a depth of 5 to 7 inches, or 1/2 to 2/3 of the thickness of the wattle.
Start building trenches and installing wattles from the base of the slope and work up. Spread excavated material evenly along the uphill slope and compact it using hand tamping or other methods.
Construct trenches at contour intervals of 10-to 25- feet apart depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches .
Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12 inches behind one another.
Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle.
If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil.
Wooden stakes should be approximately 0.75 x 0.75 x 24 inches min. Live cuttings or 3/8-inch rebar can also be used for stakes.
Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake protruding above the wattle.
Wattles may require maintenance to ensure they are in contact with soil and thoroughly entrenched, especially after significant rainfall on steep sandy soils.
Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted or water has scoured beneath the wattles.
Figure 3 - 25: Straw Wattles