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<br />u. S. ARliY ENG:rnELRS REPORT (CCillT ID) <br /> <br />Since the same design storm was employed by each agency, the <br /> <br /> <br />difference in opinicn may be said to be due to differences in assumed run- <br /> <br />off rates and amounts. The question of rainfall-runoff' relations, and <br /> <br />the degree to which runoff volumes and intensities are subject to control, <br /> <br />-y justify further investigation in advance of oonclusions as to adequac:r <br /> <br />and reascnableness of flood control designs. <br /> <br />The difference in estimated construction costs, between the <br /> <br />figures Zil,782,250 of the District Engineer (perhaps *2,300,000 as revised <br /> <br />by the Board of Engineers) and ~876,500 of the Bureau. is in part due to <br /> <br />the increased flood storage capacity provided below the overflon spillway <br /> <br />level, but prinoipally is due to the differenoe in overflow spillway <br /> <br />design. The Bureau, having estimated the total runoff from the lll8.Ximwn <br /> <br />flood and having provided sufficient oapaoity to impound that volume, <br /> <br />inoluded only.minor additional factors o~.isafety. The Axmy provided against <br /> <br />a flood 150 peroent of the reservoir design flood, and assumed suoh a flood <br /> <br />might ocour with the reservoir full to spillway ores'll and the outlets <br /> <br />fully plugged. This additional protection is obtained by 35.5 feet in <br /> <br />depth of suroharge storage, and an overflow spillway lCJO.ofeet wide running <br />. , <br /> <br />35.5 feet deep (with 5.0 feet of freeboard remaining belov! the top of the <br /> <br />,., <br /> <br />dam), thus discharging 82,000 seo. ft. and ore"ting surcharge storage <br />(above spillway crest) of 28,500 aoreNfeet. <br /> <br />,In addition to Castlewood Dam andReservQ~r"the flood <br /> <br />control plans of the Axmy include the construction of ,Cherry Creek Dam . <br /> <br />and Re.servoir No. I, about one mile above the existing Sullivan Barrier. <br /> <br />This dam with a height of l04-feet above stream bed and a length of 8,550 <br /> <br />feet, '((ould serv.esqlely as a ,barrier to .retard flood waters. The. outlet <br /> <br />is unoontrolled. It has a o~paoity of.7,500,sec.rt.(when the pool is at <br /> <br />-24- <br />