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BMP: SLOPE STABILIZATION <br />1. METHODS: Rip rapping is the use of cobble-size rock, generally 6"- 10" <br />in size, placed closely together on disturbed soils to prevent erosion. Rock <br />riprap is generally the most effective erosion control device for slopes greater <br />than 30%. It can also be used on less steep slopes and works well with <br />seeding. Concrete can be used to fill in between the rocks to hold the riprap <br />securely in place, a common practice on steep slopes. <br />Slopes that are cut for building or driveway construction are sometimes so steep <br />that vegetation or rip rapping alone cannot adequately protect them. Runoff from <br />these over-steepened slopes often erodes the toe of the slope, causing continued <br />slope slippage. Retaining walls prevent toe erosion and slope slippage. <br />The following method should be used to construct a native rock retaining wall. <br />(Note: Any retaining wall over 4' high shall be designed by a licensed engineer <br />and require a retaining wall permit). <br />? Remove all large rocks from the eroding slope and stockpile on site. <br />? Dig a footing trench along the toe of the slope. <br />? Place the largest rocks in the trench with their longest axes perpendicular <br />to the slope. <br />The face of the wall may vary from <br />vertical to a 1:2 slope. <br />z? <br />? Fill the space behind the rock wall with <br />leftover soil excavated from the site. 2r hL 4- <br />4- Slope the ground at the base of the wall <br />at a 2% grade away from the wall and <br />stabilize it with vegetation or mulch. If a <br />driveway is located at the base of the <br />wall, pave it up to the wall or install a curb. <br />The following method should be used to construct a wood retaining wall. (Note: <br />Any retaining wall over 4' high and shall be designed by a licensed engineer and <br />require a retaining wall permit). <br />? Set 6" x 6" wood posts into concrete foundations at least 2' into ground. <br />Space the posts 5' apart. <br />? Nail 2" x 12" wood planks to the upslope side of posts. Leave a small <br />vertical space between planks to allow drainage at the base of the wall <br />18 <br />