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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Aro1ication of Rational !ttIxld <br /> <br />A val"..hlp use of tIE Ratiooal !ttIxld is in tIE evaluatim of a l'1uvosed subdivisim <br />drainage system. The III!thxI can be used to define the design flows at variws points in the <br />subdivisim to check the capacity of the streets, storm inlets, storm sewers, or other drainage <br />facilities. the BIIDllIIt of detail needed to evaluate each subdivision depeOOs upCIl the <br />caup1.exi.ty of the drainage system. <br /> <br />3.5 Collrado Urban ~~ l'rocelUre <br /> <br />The Colorado Urlmi HydrograJit Procedure (OUP) was origi=lly developed for the futver area <br />at the t:iJJl'! l.EIDf was prepared. The oetOOd is appli,."hlp to basins greater than 10J acres all! <br />Slall be used for watershed areas larger than 200 acres. The procedures for the <lllP, as <br />explained in the IEIDI, 1 "Runoff", shall be f~ in the PI"J.Uiation of drainage reports and <br />storm drainage facility designs in tIE Town of Ordway all! surroonding Crowley Camty area. <br /> <br />3.6 ~ Ommels <br /> <br />Open channels shall be designed for the lOO-year frequeocy storm. The channel design Slall <br />also be analyzed with respect to initial storm nmoff and its effect nade known. \hrever <br />practical, the channel should have slow flow characteristics, be wide and shallow, and be <br />natural in its appearance and functi.arlng. Coosi.deration should be given to the capacity and <br />stability of the receiving drainage system as well. <br /> <br />0-anne1s sInlld be designed in soch a IlB11lle[' that flows at tIE critical depth and <br />supercritical flows are avoided. Olannel caJllclties should be canputed fran l1mning's FornW.a <br />for uniform flow. <br /> <br />The channel cross section IIBY be alm:Jst any type suitable to tIE location. J:/oo.ever, tIE <br />limitations for design for tIE IIBjor storm and initial storm design flows shall inclWe: <br /> <br />a. Side Slopes. Side slopes for grnss-lined channels shall be as flat as practical. Side <br />slopes of 4: 1 shall be considered a nOIlIBl. mininun. uroer special conditions slopes of <br />3:111BY be Utili7e:J; ho\.ever, a slope of 4:1 is the practical limit for JJDWing <br />equijJIEllt. Concrete channe1 IIBY be used in areas where space is limited. Side slopes <br />for cmcrete channel shall not be steeper than 1: 1. <br /> <br />b. ~th. The IIBXinun design depth of flow for tIE lIBjar' storm Sxluld be limited to foor <br />feet far grass-lined channel, although depths of five feet IIBY be acceptable where good <br />channe1 naintenaoce IIBY be expected and durations of peak flows are smrt. The design <br />depth of flow for tIE initial storm nmoff should not be less than me foot. <br />Critical depths shall be investigated for both the lIBjar' and initial storm nmoffs and <br />these values nade known. <br /> <br />c. Freeboard. Except where lrr"li7e:J overflow in certain areas is desirable for <br />additional poOOing benefits ar other reasons, the mininun allowable channe1 freeboard <br />shall be: <br /> <br />7 <br />