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only an average; flood depths in some areas are eIther deeper or shallower. Furtherreflnementot llood depths In thIs area can only be achieved with the use of detailed topographic mapping which Is currently unavaIlable. U.S. Highway 6 is lower than the IOO.year flood water surface elevation of the South Platte River main flood flow whIch encom- passes the Channel and adjacent flood plain. This area Is shown on plate 9 and is IdentIfIed by two flow arrows over U.S. HIghway 6 and a note Indicating that laO-year flooding Is possible in an area otherwise designated as being In the SOD-year flood plain. A detailed aoalyslscf the hydraulic characterIstIcs of The flood plain between this section of U.S. Highway 6 and the SoUTh PlaTte River channel and adjacent flood plain Indicated that the several rallr~d embankments In This area produced sufficIent head loss to reduce IOO-year flood WaTer surlace elevations at U.S. Highway 6 to nearly the same elevatIon as the hIghway. If the SoUTh Platte River flood plaIn retains the same conveyance in The future as existed at the tlmA of the study, only a small guantlty of water will overtop U.S. HIghway 6. The resultant floodllow would be handled by existing drainage facilIties. However, If flood plain conveyancelsreduced,floodwatersurfaceelevationswilllncrease so that slgnif1cant floodwater will flow over U.S. Highway 6. These flOOdwaters wolJld gen<!rally flow In a norTheasterly direction as they spread across the flood plain In proportIon to the quantity of water overtooplng U.S. Highway 6. Development In the area subject to shallow floodIng should occur only 11 done In a manner which will considerably reduce the exposure to potentlel flood damage. In this type of flood exposure, build- Ings should be elevated whIle keeplngadjl'lcent streets 1011. The street network should be designed such that floodllaterSllll1 be carried through the area by the street neTwork without subjecting the adjacent buildings to floodwater damage. The p~tographlc background used for the Flooded Areas, plates }-12, lias made fromt\IQ sets of aerial photographs. Plates3 7 IIeremadefromonoset; plates8-12weremadefromar"lOtherset. Because 01 These different sources of photographic background and because of the Inherent distortion In low altitude aerial photographs, plaTes 3 end.S, 4 and 9, ~ and 10, etc., do not match. The result Is that physical featureSCOlTTnOntobothplateset3-7andplate set8-IZ....yhavesllghtlydlfferentlongltudlnal distencebetween them when comparIng beTween the two photo sets. Therefore, when utilIzing these plates to determine the location of the flood bound~ aries, reference should be made from t~ nedrest adjacent landmark On the pootographlc background In order to minImize longItudinal error. ObstrUCTIons to floodflows . Four roadways cross the tl<:>od plain of th<><;"IJth PI"ttoo RIver and Pawnee Creek in the area studied by thIs report. The physical characteristics of the r~d- \ldYS crossing the South Platte RIver created conditions In this study IIhlch resulted In an increase In water surface elevation Immediately upstream ~rom these roadways ranging from 0 to 2 ~eeT. Similarly, the physIcal characteristics of the roadllays crossing the Pawnee Croek flood plain created conditions In this study whiCh resulted Inadditionalfloodwalerbelngdlverted Into Sterling. Flood Conditions upstre"m from the roadway ~bankments crossing the The hydraulic aMlyslsconducted In this study on the SOuth Platte River Showed that floodwaters from The IOO-year flood generallywouldnatovertopU.S.Hlghwlly6. Thus,theFloodedArea plates show the SOuth Pllltte River IOO-year flOOd contl'llned south ..nd east from U.S. Hi~hwllY 6. However, a loclltlon does exist where " "