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CITV OF EVERcTT STORMWATER M�NAGEMENT MANUAL <br /> , <br /> � Design and Insfallatlon Specifications <br /> 1. Locate the channel where it can coniortn ro the topography and other features such as roads. <br /> 2. Locate them to use natural drainage systecns to the greatest eztent possible. <br /> 3. Avoid shazp changes in alignment or bends and changes in grade <br /> 4. Do not reshape the landscape to fit the drainage channel. <br /> 5. The ma�cimum desigo velocity s6a11 be based on soil conditions,type of vegetation,and method <br /> of revegetation,but at no times shall velocity exceed 5 feeUsecond. The channel shall not be <br /> ' oveAopped by a peak runoff rate equal to L6 times Lhe l0-yeaz, 1-hour time step flow indicated <br /> by an approved continuous ronofl model. if a I S-minute(or less)time step is used,no cortcction <br /> factor is required. <br /> 6. Where the gcass-lined channel will also function as a permanent stormwater conveyance facility <br /> the channel must meet the conveyance requirements def ned in Volumc f,Chapter 6. <br /> 7. M established grass or vegetated lining is required before the channel can be used ta convey <br /> stortnwater,unless stabilized with nets or blankets. <br /> B. If design velocity of a channel to be vegetated by seeding exceeds 2 feeUsec,a temporary channel <br /> liner is requited. Geotextile or special mulch protection such as sttaw or netting provides stability <br /> until the vegetation is fully estebGshed. <br /> 9. Temporary chock dams s6all be removed when the grass hes matured sufficiently to protect the <br /> ditch or swali+ udess the slope of the swale is greater than 4 percent. The area beneath the check <br /> dams shall be seeded and mulched irtunediately after dam removal. <br /> � 10. If vegetation is established by sodding,the petmissible velociry for established vegetation may be <br /> � used and no temporary liner is needed. <br /> 1 l. Do not subject grass-lined channel to sedimentalion from disturbed areas. Use sediment-trapping <br /> B��IPs upstream of the channcl. <br /> 12. V-shsped grass c6annels generally apply where the quantity of water is small,such as in shoct <br /> reaches along roadsides. The V-shaped cross-section is least desirable because it is difTicult to <br /> stabilize thc bottom where velocities may bc high. <br /> l3. Trapezoidal gress chaonels are used where ntnoff volumes are large and slope is low so that <br /> velocities are non-erosive to vegetated linings. (Note: it is difficult to construct small parabolic <br /> shaped channcls.) <br /> 14. Subsurface drainage,or riprap channel bottoms,may be necessary an sites that are subject to <br /> ptolauged wct conditions due to long duration ilows or a high water tablc. <br /> 15. Provide oudet protection at culvcrt ends and at channel inicrsections. <br /> 16. Grass channcls,at a minimum,should carry peak runoff fortemporary consWction drainagc <br /> facilities Gom l.6 times the 10-year, 1-hout time step tlow Gom an approved continuous model. <br /> WFiere flood hazard exists,the r•pacity shall be increased accarding to the potential damage. <br /> 17. lirassed channel side slopes generally are constcucted 3:1 or flatter to aid in the establishment of <br /> vegetation and for maintenance. <br /> l8. Construct channels a minimum oF 0.2 foot latger around t}io periphery to allow for soil bulking <br /> during seedbed prepamtions and sod buildup. <br /> Volume II—Construction StormwaterPollution Prevention <br /> 3-3d <br />