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thickness is 2 feet. <br />For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), use an <br />engineered energy dissipator. <br />Filter fabric or erosion control blankets should always be used under riprap to prevent <br />scour and channel erosion. See BMP C122: Nets and Blankets. <br />. Bank stabilization, bioengineering, and habitat features maybe required for disturbed areas. <br />This work may require a Hydraulic Project Approval (H PA) from the Washington State Depart- <br />ment of Fish and Wildlife. See 1-2.11 Hydraulic Project Approvals. <br />Maintenance Standards <br />Inspect and repair as needed. <br />. Add rock as needed to maintain the intended function. <br />- Clean energy dissipator if sediment builds up. <br />BMP C220: Inlet Protection <br />Purpose <br />Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- <br />bilization of the disturbed area. <br />Conditions of Use <br />Use inlet protection at inlets that are operational before permanent stabilization of the disturbed <br />areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and <br />within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment <br />trapping BMP. <br />Also consider inlet protection for lawn and yard drains on new home construction. These small and <br />numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof <br />drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap <br />these drains to prevent sediment from entering the system until completion of landscaping. Provide <br />18-inches of sod around each finished lawn and yard drain. <br />Table 11-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods <br />for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain- <br />age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with <br />additional end -of -pipe treatment where stormwater ponding would cause a hazard. <br />2019 Stormwater Management Manual for Western Washington <br />Volume /I - Chapter 3 - Page 356 <br />