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1 <br />Table 11-4.1.8 Mulch Standards and Guidelines (continued) <br />Mulch <br />Quality <br />Application <br />Material <br />Standards <br />Rates <br />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 nets, but cover the ground more completely. Coir (coconut <br />fiber) fabric comes as both nets 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:1 V, 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 />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />Volume 11 - Chapter 4 - Page 288 <br />1 <br />