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BMP C120: Temporary and Permanent Seeding <br /> Purpose Seeding is intended to reduce erosion by stabilizing exposed soils. A <br /> well-established vegetative cover is one of the most effective methods of <br /> reducing erosion. <br /> Conditions of Use • Seeding may be used throughout the project on disturbed areas that <br /> have reached final grade or that will remain unworked for more than <br /> 30 days. <br /> • Channels that will be vegetated should be installed before major <br /> earthwork and hydroseeded with a Bonded Fiber Matrix. The <br /> vegetation should be well established(i.e., 75 percent cover)before <br /> h Withchannelsthat will have water is allowed to flow in the drtc a e <br /> high flows, erosion control blankets should be installed over the <br /> hydroseed. If vegetation cannot be established from seed before water <br /> is allowed in the ditch, sod should be installed in the bottom of the <br /> ditch over hydromulch and blankets. <br /> • Retention/detention ponds should be seeded as required. <br /> • Mulch is required at all times because it protects seeds from heat, <br /> moisture loss, and transport due to runoff. <br /> • All disturbed areas shall be reviewed in late August to early September <br /> and all seeding should be completed by the end of September. <br /> Otherwise, vegetation will not establish itself enough to provide more <br /> than average protection. <br /> • At final site stabilization, all disturbed areas not otherwise vegetated or <br /> stabilized shall be seeded and mulched. Final stabilization means the <br /> completion of all soil disturbing activities at the site and the <br /> ' establishment of a permanent vegetative cover, or equivalent <br /> permanent stabilization measures (such as pavement,riprap, gabions <br /> or geotextiles) which will prevent erosion. <br /> ' • Seeding should be done during those seasons most conducive to <br /> Design and growth and will vary with the climate conditions of the region. <br /> Installation Specifications Local experience should be used to determine the appropriate <br /> seeding periods. <br /> • The optimum seeding windows for western Washington are April 1 <br /> ' through June 30 and September 1 through October 1. Seeding that <br /> occurs between July 1 and August 30 will require irrigation until 75 <br /> percent grass cover is established. Seeding that occurs between <br /> ' October 1 and March 30 will require a mulch or plastic cover until <br /> 75 percent grass cover is established. <br /> • To prevent seed from being washed away, confirm that all required <br /> surface water control measures have been installed. <br /> February 2005 Volume ll—Construction Stormwater Pollution Prevention 4-13 <br />