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Table 11-4.1.8 Mulch Standards and Guidelines (continued) <br /> Mulch Quality Application <br /> Material Standards Rates Remarks <br /> high length- <br /> to-width <br /> ratio. <br /> BMP C122: Nets and Blankets <br /> Purpose <br /> Erosion control nets and blankets are intended to prevent erosion and hold seed and <br /> mulch in place on steep slopes and in channels so that vegetation can become well <br /> established. In addition, some nets and blankets can be used to permanently reinforce <br /> turf to protect drainage ways during high flows. Nets (commonly called matting) are <br /> strands of material woven into an open, but high-tensile strength net (for example, <br /> coconut fiber matting). Blankets are strands of material that are not tightly woven, but <br /> instead form a layer of interlocking fibers, typically held together by a biodegradable or <br /> photodegradable netting (for example, excelsior or straw blankets). They generally have <br /> lower tensile strength than nel:s, but cover the ground more completely. Coir(coconut <br /> fiber)fabric comes as both nel:s and blankets. <br /> Conditions of Use <br /> Erosion control nets and blankets should be used: <br /> . To aid permanent vegetated stabilization of slopes 2H:1V or greater and with more <br /> than 10 feet of vertical relief. <br /> . For drainage ditches and swales (highly recommended). The application of appro- <br /> priate netting or blanket to drainage ditches and swales can protect bare soil from <br /> channelized runoff while vegetation is established. Nets and blankets also can cap- <br /> ture a great deal of sediment due to their open, porous structure. Nets and blankets <br /> can be used to permanently stabilize channels and may provide a cost-effective, <br /> environmentally preferable alternative to riprap. 100 percent synthetic blankets <br /> manufactured for use in ditches may be easily reused as temporary ditch liners. <br /> Disadvantages of blankets include: <br /> . Surface preparation required. <br /> . On slopes steeper than 2.5H:1V, blanket installers may need to be roped and har- <br /> nessed for safety. <br /> . They cost at least$4,000-6,000 per acre installed. <br /> Advantages of blankets include: <br /> 2014 Stormwater Management Manual for Western Washington <br /> Volume ll- Chapter 4 -Page 288 <br />