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<br />Because the deten.tion storage "lOuld bE? empty most. of the 'I:ime <br />and the embankmen.t will contain the 100-.year storm eVE,nts for <br />relatively short periods of time, seedinq was used for embank- <br />ment protect.ion. Riprap was provided for spillway protect:ion <br />if at1 emergency spillway overflow occurred. Concrete lined <br />spillway is also a feasible al ternaLLve. Bot:h riprap and <br />conc~ete lined spillways should be investigated in detail in <br />t:he final design. The detention facili t:i.es on Lowry .I\.ir Force <br />Base were designed by t:he Omaha :'Jis1:rict. Corps of Engineers. <br /> <br />!lydn.ulics <br /> <br />Hydraulic analyses were complet:ed b) det:erminethe wat:er <br />surface elevations for the 2- r 10..., and lOa-year ston~ <br />events and the Standard Project Flood for the existinq <br />basil1 condit.ions durin') the Phase A (;tud:ies. The elevations <br />were compiled using the Corps of Engineers I.!EC-2 Wa teJ~ <br />Surface Profile computE?r program. Channel cross sect:ions <br />were measured on the 1" = 100' sea 1," " 2-.ft contour, topo.- <br />graphic mapping provided by the District. A field investi- <br />gati:m was conducted to de1:ermin'2 the channel and flood <br />plain condit.ions, vege1:ative c()v.:~r, dnd rou(jhness cOE~fficient. <br /> <br />'l'he 11 values used for the bachvater computa'U.ons WerEl: <br /> <br />R.C. box culverts <br />R.C. pipes <br />:~orruga t.ed Metal Pipes <br />'ljatural Channels <br /> <br />n = 0,015 <br />n .- O. 0 13 <br />n r). '')23 <br />n - 0.035 to 0.050 <br /> <br />Contr:action and expansion loss coef:E.i.ciE,nts ",ere assigned as <br />foll:)ws: <br /> <br />Con-traction <br /> <br />~~Xl=:~~~~ ior~ <br /> <br />Chan.:1el to channel with gradual <br />Ch'ln')e in area <br /> <br />O.J <br /> <br />0..3 <br /> <br />Chan:'lel to channel or culvert <br />wi th abrupt chanqe in an?a <br /> <br />I). :0: <br /> <br />005 <br /> <br />To d'~termine associated losses ,. the"c, values were applied to <br />the respective changes in velocity head. <br /> <br />Bridge and culvert loss coefficients wel~ assigned according <br />t:o tile values lis.ted in the IlEC.-2 USCl:CS nanual, October, 1973. <br /> <br />The details of flood plain and floodvray determina.tion were <br />pres3nted in the Flood Hazard llrea Delineation Report: for <br />Vlest':!rly Creek by Camp Dresser & Nc]\("~ I:l.c.. in January, <br />1977. <br /> <br />.-18.. <br />