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<br />. <br /> <br />. <br /> <br />. <br /> <br />00lU37 <br /> <br />, <br /> <br />Chapter 3--Dosigns and Estimates <br /> <br />HlTROD:;CT ION <br /> <br />The Branch of Design and Construction has prepe,rod two estimat.es <br />for a dum at the Braziel site. Ono provides for a spill~ay capacity <br />of 2,75G cfs, the other for a spillway capacity of 784 cfs. The <br />final dosign will probably previde for n capacity between those two. <br />Details of both estimates are discussed herein, with emphasis on the <br />larger for tho pur?oso of d0~icting maximum costso <br /> <br />GEOLOGY <br /> <br />Resarvoi~" A:r8D. <br />-------- <br /> <br />The resorvoir areD. is 1 )ca-ced on tho high plain~ "bout nine <br />milos south of tho No,..l;h Plat"o River, which has eut a deep wide valloy <br />exposing nlmo3'I; 1,000 feet of . \early horizontal Tertiary 5edimont;s. <br />The bedrock in this area is com 10sod of tVIO fOI'matio",s of noc.rly <br />horizontal s8dimonts. The up,Jor, or ChadI'on formcctio"', consis'cs <br />princi;~ally of grccn and orown plastic clay wi th somo silty layor~ of <br />volcanic ash, all of '.'Ihich ercde oasily and form flr.t slopes, The <br />undcrly),ng Lance formation, of Crctacoous ago, is composed of inter- <br />oeddod variegated claystonos and brown sofe sWldstones, This formG- <br />tion is confined to tho lO:i}or elevations in the resorvoir nrca., except <br />at tho dc.msi te where tho stroam has cut into a buriod hill of 1.."-DOO <br />sediments, T11C sandstone rlcmbcrs ma.y 80 1;1f:'~tcr bc::;.ring~ The reservoir <br />o.rc=:. is covered rlith silty and s,n.ndJr lOl]J]1s on c;cntlo slopos and is <br />mostly irrigated. Losses from seopage "Iould bo unim,Qort::m'c. <br /> <br />. <br /> <br />Dcrnsito <br /> <br />The ontire darn foundation would rost on tho soft sandstones c.nd <br />claystones of tho Lanco formation. Tho Lance formction is composod <br />of sediments, oxtromoly interbedded wld 10nsed in characte'~. Tho <br />.rormc.t;io~ dips very gently to the nort;h\'Josi:;~ The ol}"crbu~:ton attains <br />a maximtUn depth of r.bout 41 feet on the left side of tho valloy. Tho <br />'.1ervious nuctoria1. veeries from silty to sc..ndy loam Hith silty fino- <br />!;r,-,ined S"llds ImlGing in benoo.th tho 10D.ln covor in tho dee [Oe!" prcrts of <br />the valley alluvium. Tho Lo.lloe sediments Qrc rolc.tivoly soft oxocpi:; <br />for 0. fow scatt.ered concretionary ledges o.nd smo.ll boulders of hc.rd <br />s~ndstonQ ~nd limestone. <br /> <br />From the information guinod by prossure tosts in the drill holes <br />no signifioant leakago would normally bu r.nticipl\tcd in the bcdro.)k <br />Hoy,evor. t"c nl\ture of tho sr.ndstone l"ycrs found intorbeddod c.nd <br />intcrfingored with t.he imporvious elo.ystoncs -i1~die"t8 timt prcoau-tj,I1ns <br />should be to.kcn to blanke.1:; 0.11 sandst.nnc CXQUS'JrLl in tnn rl.nnlsito areD. <br />wi th l\n imrervious oapping;. <br /> <br />42 <br />