819 N BROADWAY WASHINGTON STATE UNIVERSITY 2018-05-11

BMP C122: Nets and Blankets Purpose Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on steep slopes and in channels so that vegetation can become well established. In addition, some nets and blankets can be used to permanently reinforce turf to protect drainage ways during high flows. Nets (commonly called matting) are strands of material woven into an open, but high-tensile strength net(for example, coconut fiber matting). Blankets are strands of material that are not tightly woven, but instead form a layer of interlocking fibers,typically held together by a biodegradable or photodegradable netting(for example, excelsior or straw blankets). They generally have lower tensile strength than nets, but cover the ground more completely. Coir(coconut fiber) fabric comes as both nets and blankets. Conditions of Use Erosion control nets and blankets should be used: • To aid permanent vegetated stabilization of slopes 2H:1 V or greater and with more than 10 feet of vertical relief. • For drainage ditches and swales (highly recommended). The application of appropriate netting or blanket to drainage ditches and swales can protect bare soil from channelized runoff while vegetation is established. Nets and blankets also can capture a great deal of sediment due to their open, porous structure. Synthetic nets and blankets can be used to permanently stabilize channels and may provide a cost-effective, environmentally preferable alternative to riprap. 100 percent synthetic blankets manufactured for use in ditches may be easily reused as temporary ditch liners. Disadvantages of blankets include: • Surface preparation required; • On slopes steeper than 2.5:1, blanket installers may need to be roped and harnessed for safety; • They cost at least$4,000-6,000 per acre installed. Advantages of blankets include: • Can be installed without mobilizing special equipment; • Can be installed by anyone with minimal training; • Can be installed in stages or phases as the project progresses; • Seed and fertilizer can be hand-placed by the installers as they progress down the slope; • Can be installed in any weather; • There are numerous types of blankets that can be designed with various parameters in mind. Those parameters include: fiber blend, mesh strength, longevity, biodegradability, cost, and availability. 4-22 Volume II—Construction Stormwater Pollution Prevention February 2005