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CITV OF EVERETT STORMWATER MANAGEMENT MANUAL <br /> ) <br /> example,coconut fibcr matting). Blankets are shands of matcrial that are not tightly woven,but instead <br /> fortn a layer of interiocking fibers,typically held toget6er by a biodcgradable or photodegradable netting <br /> (for example,excelsior or straw blankets). They gencrally havc lower tensile strength than nets,but cover <br /> the ground more completely. Coir(coconut fiber) fabric comcs as both nets and blankets. <br /> Conditions of Use <br /> Erosion control nets and blankets shouid be uscd: <br /> 1. To aid pertnaneot vcgetated stabilization of slopes 2H:l V or greater and witl�morc than 10 feet of <br /> vcrtical relief <br /> 2. For drainege ditches and swales (highly recommended). The epplication of appropriate netting or <br /> blanket to drainage ditches and swales can protect bare soil from channeliud runoff while <br /> vegetation is established. Nets and blankets also can caphuc a great deai of sediment due to their <br /> open,porous structure. Synt6ctic nets and blankets can be used to permaoently stabilize channcls <br /> aod may providc a cast-ellective,environmeotally preferable altemauvc to nprap. Onc-hundrad <br /> perceot synthetic blankets manufachucd for use in ditches may be casily rwsed as temporary <br /> ditch lincrs. <br /> Disadvantages ofblanketsioclude: <br /> 1. Surface preparation is required <br /> 2. Ou slopes steepet t6an 2.SH�I V,blanlcet installers may need to be roped and hemessed for safety <br /> 1. They cost at leazt$4,000 to 56,000 p;r acre installed. <br /> Advantages of blankets include: <br /> 1 I. Can be installed without mobilizing special equipmcnt <br /> I 2. Can bc installcd by anyone with minimal haining <br /> 3. Can be installed in s:agcs or phases as the project progresses <br /> 4. Seed and fertilizcr can bc hand-placcd by thc installers as thcy progress down thc slopc <br /> 5. Can be installed in any wcather <br /> 6. Therc aze numcrous types of blankets thet can bc designed with verious paramctcrs in mind. <br /> Those parameters include: fiber blend,mesh shength,longevity,biodegradability,cost,and <br /> aveilability. <br /> Oesign andlnstallaHon Specircations <br /> 1. Sec DCSS Drawing q20).for typical orientation xnd installation of blankets used in channels aed <br /> as slopc protection. 1Jote: Thcse are oniy typical cxamplcs; all blankets must be installcd per <br /> manufecturer's installation instructions. <br /> 2. lnstallation is critical to the effectiveness of these products. If good ground contact is n�t <br /> achicvcd, runofTcan concentrate under the product,resulting in signific3nt erosion. <br /> 3. Installation of Blaniccts on Slopes: <br /> a. Complete f nal gradc and Vack walk up and dowo thc stopc. <br /> b. Install hydromulch with secd znd fcrtilizer. <br /> c. Dig a small Vench,approxima:el� 12 inches wide by 6 inches deep along the top of thc <br /> slope. <br /> Volume il—Construction SformwaterPollution Prevention <br /> 3-16 <br />