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1 <br /> manent stabilization measures (such as pavement, riprap, gabions, or geotextiles) <br /> which will prevent erosion. <br /> Design and Installation Specifications <br /> Seed retention/detention ponds as required. <br /> Install channels intended for vegetation before starting major earthwork and hydroseed <br /> with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install <br /> erosion control blankets over hydroseed. Before allowing water to flow in vegetated ' <br /> channels, establish 75 percent vegetation cover. If vegetated channels cannot be estab- <br /> lished by seed before water flow; install sod in the channel bottom—over hydromulch <br /> and erosion control blankets. <br /> • Confirm the installation of all required surface water control measures to prevent <br /> seed from washing away. 1 <br /> . Hydroseed applications shall include a minimum of 1,500 pounds per acre of <br /> mulch with 3 percent tackifier. See BMP C121: Mulching (p.284)for specifications. 1 <br /> • Areas that will have seeding only and not landscaping may need compost or meal- <br /> based mulch included in the hydroseed in order to establish vegetation. Re-install <br /> native topsoil on the disturbed soil surface before application. <br /> . When installing seed via hydroseeding operations, only about 1/3 of the seed actu- <br /> ally ends up in contact with the soil surface. This reduces the ability to establish a <br /> good stand of grass quickly. To overcome this, consider increasing seed quantities <br /> by up to 50 percent. <br /> • Enhance vegetation establishment by dividing the hydromulch operation into two <br /> phases: <br /> 1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier <br /> onto soil in the first lift. <br /> 2. Phase 2- Install the rest of the mulch and tackifier over the first lift. <br /> Or, enhance vegetation by: <br /> 1. Installing the mulch, seed,fertilizer, and tackifier in one lift. <br /> 2. Spread or blow straw over the top of the hydromulch at a rate of 800-1000 <br /> pounds per acre. <br /> 3. Hold straw in place with a standard tackifier. <br /> Both of these approaches will increase cost moderately but will greatly improve <br /> and enhance vegetative establishment. The increased cost may be offset by the <br /> reduced need for: ' <br /> 1 <br /> 2014 Stormwater Management Manual for Western Washington <br /> Volume II- Chapter 4 -Page 279 ' <br />