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BMP C201: Grass-Lined Channels <br />Purpose <br />Condi(ions of Usc <br />Dcsign and <br />lrrsmllution <br />Spccificafions <br />To providc a channel with a vcgetativc lining for convcyancc of runofi�. <br />Sce Figure 4J for typical grass-lined channcis. <br />This practicc applics to canswction sitcs �vhcre conccntratcd runofi�nccd: <br />to bc cantaincd to prevcnt crosion or Ilooding. <br />• \Vhen a vegeiativc lining can provide sufficient stabiliry for the <br />channel cross section and al lower velocities of water (nomially <br />dependent on gradc). This mcans that the channcl siopcs are gen�nlly <br />Icss than 5 peroent and spacc is availablc for a rclativcly largc cross <br />scctiun. <br />• Typical uses include madside ditches, channels at propeny boundarics, <br />outicts for diversions, and other channels and drainage ditches in low <br />ilfl'85. <br />Channels that will be vegetated should be installed before major <br />eanh�cork and h}•droseeded aith a bonded fiber matris (Bfht). The <br />vegeiation should be �eell esiablished (i.e., 7> pereent co��er) before <br />�satcr is allo�ti�ed to ilo��� in the ditch. \Yith diannels ihat will haee <br />hieh flo���s, crosion control blankets should be installed over thc <br />hydrosecd. Ifvegetation cannot be established from sced before a•:+�cr <br />is allowed in the ditch, sod should be installed in the bottom of the <br />ditch in lica of hydromulch and blankcts. <br />Locatc the channcl wherc it can cunfomi w the topography and othcr <br />fcaturc, such as roaJs. <br />• Locate them to use natur.d dninagc systems to ihe greaicst estent <br />possiblc. <br />• Avoid sham changes in alignmen� or Uends and changes in grade. <br />• Do not resh�pc thc I;�ndscapc �o fit thr dr.�inagc channcl. <br />. Thc ntaximum dcsign ��elocity shall bc bascd on soil conditions, typc <br />of veget:uion, and method of revegetation, but at no times shall <br />��clocity excecd 5 feet/second. The ch�nncl shall nut be overtopped by <br />tlic pr.�k nmofF t?om a 10-ycnr, 24-hour storni, assuming a Type I A <br />rainfall distributiun." Altcmativcly, usc L6 timcs thc 10-ycar, I-hour <br />tlow indicatcd hy vi approacd continuous nmoff modcl to detemiinc a <br />Ooµ� ntc ���hich thc channcl must coNain. <br />• �Vhcre thc gr.iss-lincd chnnncl �eill also fimction as a pcnnancnt <br />storn�watcr convcy.mcc facility, consultam Ihc drnin.�gc com�cyancc <br />n;quiremcnts of �hc local govcrnmcnt with jurisdiction. <br />• An extahlished grass or vegetated lining is required before the channcl <br />can bc used to con��cy storm���atcr, unlcss stubilizcd with nc�s or <br />blankcts. <br />February 2005 Volume ll — ConsWcfion Stormwater Pollutron Prevenfion 4•59 <br />