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INTER WEST — EVERETT CONTRACTOR'S YARD INTERIM FILL PROJECT Sitts & Hill Engineers, Inc. <br />CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN Job Number 17,733 <br />Table 11-4.1.8 Mulch Standards and Guidelines (continued) <br />Mulch <br />Quality <br />Application <br />Remarks <br />Material <br />Standards <br />Rates <br />high length - <br />to -width <br />ratio. <br />BMP C122: Nets and Blankets <br />Po nose <br />Erosion ^ontrol nets and blankets are intended to prevent erosion and hold seed and <br />mulch in pi';ace on steep slopes and in channels so that vegetation can become well <br />established. i,-) addition, some nets and blankets can be used to permanently reinforce <br />turf to protect drainage ways during high flows. Nets (commonly called matting) arr <br />strands of material .voven into an open, but high -tensile strength net (for exam <br />coconut fiber matting). Blankets are strands of material that are not tightly w en, but <br />instead form a layer of in;-�rlocking fibers, typically held together by a bind gradable or <br />photodegradable netting (f(,~ example, excelsior or straw blankets). Th �•y generally have <br />lower tensile strength than nei: , but cover the ground more complet ;ly. Coir (coconut <br />fiber) fabric comes as both nets and blankets. <br />Conditions of Use <br />Erosion control nets and blankets should Le used: <br />• To aid permanent vegetated stabilizatior f pes 2H:1 V or greater and with more <br />than 10 feet of vertical relief. <br />• For drainage ditches and swales (hialily recommended). The application of appro- <br />priate netting or blanket to drainaP ditches and s�, ales can protect bare soil from <br />channelized runoff while vege ion is established. Nits and blankets also can cap- <br />ture a great deal of sediment due to their open, porous\ cture. Nets and blankets <br />can be used to permane stabilize channels and may p vide acost-effective, <br />environmentally prefe le alternative to riprap. 100 percent nthetic blankets <br />manufactured for u in ditches may be easily reused as tempo ditch liners. <br />Disadvantages of bl kets include: <br />• Surface pr aration required. <br />' . On sl es steeper than 2.5H:1 V, blanket installers may need to be roped an <br />ne ed for safety. <br />hey cost at least $4,000-6,000 per acre installed. <br />vantages of blankets include: <br />2014 Stormwater Management Manual for Western Washington <br />Volume 11- Chapter 4 - Page 288 <br />SITTS & HILL ENGINEERS, INC. 40 <br />' TACOMA, WASHINGTON <br />