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BMP C202: Channel Lining <br />Purposc <br />Conditrnnr njt�sc <br />D�sign und <br />bulallatinn <br />Specifrcadans <br />To protcct crodible channcls by pmviding a channcl lincr using cithcr <br />blankcts or riprap. <br />\Vhen n�rtur.d soils or vegctated stabilized soils in a channcl are not :idcquat� <br />to prc�•eN channcl crosion. <br />. When a pennaneN ditch or pipe syslem is to be installed and a <br />tcmporsry tncasurc is necJcd. <br />• In almost all cases, synthetic and organic coconut blankets are more <br />efTecti�c than ripr.ip for protecting channels from erosion. E3lankets <br />can be uscd with and without vcgetation. Blankcicd channels can be <br />dcsigncd to handle any espected ilo�� and longevity requiremeni. <br />Somc synthctic blankcts ha��c a prcdictcd lifc span of 50 years or <br />more, even in sunlight. <br />. Other reasons why blankets �re bctter than �'ock include the a�•ailabilit}� <br />of blankets over rock. In many areas of the state, rock is not easily <br />oMain�blc or is �•ery expensive to haul to a sitc. E3lankets can bc <br />deli��ered any�ehere. Rock requires the use of Jump tnicks to haul and <br />hca�y cquipmcnt to placc. Blankets usually cnly rcquirc laborcrs ��'ith <br />h:tnd rools, and somctimcs a backhoe. <br />•'fhe Federal fiighway Administration recommends not using flexiblc <br />liners u•hene��er the slope cxceeds 10 percent or the shear stress <br />cxcecds 8 Ibs/fl'. <br />Scc BMP C122 for infonnatiun on blankcts. <br />Sincc riprap is uscd whcrc cro.ion potcntial is high, conswction must bc <br />sequenced so tha� thc riprap is put in place �t�ith the minimum possible <br />dclay. <br />. Disturb:�ncc of arcas ��•hcrc riprap is to bc placcd should be undcrt:�kcn <br />only whrn fin:d prcpar�tion and placcmcn� of �hc riprap can follow <br />immediatcly beliind the iniiial disturbance. 1Vhere ripr.�p is wcd Cor <br />outict protcction, �hc ripr:ip should hc placcd hcfore or in conjunction <br />�eith tlie consin�ction of the pipe or chamiel so that it is in place when <br />thc pipc or channcl bcgins �o operatc. <br />• 7�hc dcsigncr, aflcr dctcm�ininti �he riprap sizc tha� �vill bc stablc undcr <br />ihc flow conditions, shall considrr that sizc to bc a minimurn sizc and <br />�hcn, bascd on riprap gradations actu:illy availablc in thc :ucn, scicct <br />the size or sizcs that cqual or escced ihe minimum sizc. Thc <br />possibility of dr.iinagc stnicturc damagc by children shall be <br />considerod in sclecting � ripnp size, especially if there is ncarby water <br />or a gully in which to tosti thc stancs. <br />• Smne for riprap sh;dl consisl of ficld stonc or quarry stonc of <br />approaimatcly rcclangular shapc. Thc stonc shall bc hard and angular <br />and of such quality thai it will not disintcgr�tc on cxposurc to ���atcr or <br />February 2005 Volume ll — ConsWcfion Stormwater Pc4ution Prevenfion 4•63 <br />