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• If design ��clocity of a channel to be vegeuited by secding excceAs 2 <br />Nsec, a temporary channel liner is requircd. Geolextile or special <br />mulch protcction sudi as fibcrglass ro��ing or stra��� and netting providc <br />stability until the �•egetation is fully established. See Figure 4.9. <br />. Chcck dams shall bc rcmovcd u•hcn thc grass has moturcd sut7icicndy <br />to protect Ihc ditch ur s���ale unless the slope of the swale is greater <br />d�an 4 perccm. Thc arca bcncath thc check dams shall Uc scrdcd and <br />mulched immediatcly aficrdam remo�al. <br />• If ��cgew�irni is cstablishcd by sodding, thc pcm�issihlc vclocity for <br />cstablished ��egetation may bc used and no temporary lincr is nccdcd. <br />• Do not subject grass-lined channel to sedimentaiion Gom disturbed <br />arcas. Usc scdimcnt-trapping B\1Ps upstrcam of thc channcl. <br />•�'-shaped grass channels generally apply �vhcre thc yuantity of w•atcr <br />is small, such as in short reaches along roadsides. The V-shaped cross <br />scction is Ieast desirable hecause it is di0icult to stabilize the hottom <br />�chere velocities may be high. <br />• Trapezoidal grass channels are uscd whcrc runoff �•olumes are large <br />80(I SIOFIC IS ION' SO lll.0 ��clocities are noncrosi��e to vegctatcd linines. <br />(Note: it is difTicult to conslnict small parabolic shaped channels.) <br />• Subsurface drainage, ur ripnp channel bottoms, may be necessary on <br />sitcs that are subjcct to pro�ongcd ��•et conditions duc to long duration <br />(lows or a high watcr tablc. <br />• Pm� idc oudc� protcction at culecrt cnds and at channcl imcrscctions. <br />• Gnss channels, at a minimum. should carry pcak nmotf for temporan <br />consiniction drainaee t:rcilities Gmn the 10-y�ar, 24-hour stomi <br />wi�hout eroding. \1'here tlood hazard exists. incr�ase Ihe cap�rity <br />according to Ihe po�cntial damagc. <br />• Grassed channcl side slopes generally arc constnictcA 3:1 or (latter tu <br />aid in thc cstahlishnuni ol'vcgctation and for maintcnanrc. <br />• Constnict channcls a minimum of 0? (uut largcr around thc periphcry <br />tn allow for soil bulking during scedbcd prcparalions and sod builJup. <br />�lfainlriwnre During the establishntent period, check gr.�ss-lin,�d channels aficr cecry, <br />SlandurJ.e r.iinfall. <br />• Afler grass is established, periodically chcck the channcl; check il afler <br />cvcry hcavy rainfall evcnt. hnmcdiatcly makc rcpairs. <br />• 11 is particularly important to chcck thc channcl outlet and all ro:�d <br />crussings for hank stahility and evidencc of piping or scour holes. <br />• Rcmo�•c all significant scdimcnt accumul:uions io maintain thc <br />dcsigncd carrying capacity. Kccp thc gnss in a hcalthy, vigorous <br />condition at all times, since i� is the primary crosion protection Ibr tLc <br />channcl. <br />4-60 Volume !! — Consfruc(ion Stonnwafer Pollufion Prevention February 2005 <br />