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<br />""'-. . <br /> <br />3-04. Spil1way~'; -' Elised upon the hydrological considerations dis.. <br />eussed in appendix I, the spillway would be an uneontrolled rectangular <br />. section having a width6f 75 feet and crest at elevation,62U.0. The <br />spillway:would.consist. of an approach ch~el, a cohcrete 6gee weir <br />sectil:ln; reinforeed. concrete retaining wall and an outlet channel. "'he <br />. ".design of.an unlined approaeh and outlet eh,umel was based p:i:'imarily <br />upon the premise of infreqU3nt spillway operation and also on the ' <br />.. existenCe of a fairly sound and et'osion-resistant sandstone. The un- <br />.. .:':qned.'trapezoidal. approaeh channel wowo. have a 75.,foot bottom width, <br />. . . .'s:lde . Slopes of 20 on 1 in the sandstone. formation, and a zero slope. , <br />to. reduce.the velocity(:)f flow. Velocities in the approa.ch ehannel <br />would generally be less than 3 feet per second. The weir seetion <br />would be 'ogee in shapEl so that mrodmum efficiency of disehilrge will be <br />. i;>btained. The spillway 'is designed 'to pass a. maximum diScharge of <br />about 5, scp-.cnbio feet per seecnd. the peak outflow resulting from the <br />spillway desit;n flood.. Maximum vrliter surfaee would be at Hev<ition <br />62J:g.Z,. A spillway rating curve was. eomputed for the ogee weir section <br />hi. the method as outlined in the preliminary draft Of. .Part CXVI, . <br />Chapter 3 of the Engineering Manual for Civil WorkS, using the relation- <br />ship ,.. . <br /> <br />Q ~. cm3/2 <br /> <br />.:~- . <br />,.""r <br /> <br />Q = discharge in e.f .s. . <br />L= length of spillway crest ih'feet <br />H = head on crest in feet <br />C = diseharge coefficient (0 = 3.S7 for <br />design nead <br />..of'-.O ~t.) <br /> <br />.~he spillway rating curve is 'shown on. plate 2 of the project repdrt. <br />Computations for the maximum wate:r surface profile indieated that <br />critical depth for a diseharge of 5 g~ eubie feet per seeondwould <br />oceur on the ogee curve just below the spillway crest. In order to <br />retain the embanlanent and to protect the embankment, a concrete re- <br />taining wall would extend from Station 1 f. 55i. to Station 3 I- ~5B <br />along the right side of the spillway. The retaining wall downstream <br />from the spillway crest would haVe a minimum freeboard of 3 feet above <br />the computed maximUll\ water surface profile. The outlet channel would <br />be trapezoidal in shape, have a 75-foot bottom width, and side slopes. <br />of 20 on 1 in the sandstone formation. The outlet ehannel would be <br />excavated partly in an erosion-resistant sandstone on a slope of <br />0.01000. The maximum velocity of flow through the autlet channel <br />would be 2.7 feet per seeond. The frietion slope was determined by <br />. Manning's formula utilizing a ro~hness eoeffieient of 0.03~. <br /> <br />where <br /> <br />- -, <br /> <br />-< <br /> <br />-5- <br /> <br />Appendix II <br /> <br />.. <br /> <br />