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SECTION 4 - HYDRAULICS Flood profiles ~nd the floodplain deline~tion generiJ.ted by the Gingery Study were incorporated into this study for the reach upstream of Drake Road. An analysis of the possible error in the floodplain elevations resulting from the slight differences between the hydrology generated in this study and the previous Masterplan was performed. It was determined these differences in floodplain elevation generally were less than 0.2 feet. The following ,able 8 presents flood elevation data. ....1 General The hydraulic analysis of Spring Creek WiiS ~ompleted using the U.S. Army Corps of Engineers step-back\olater compllter model JIEC- 2. Digitized cross sections were based on March 1936 photogrammctry. 8ridge and culvert geometries were field measured. Manning's rou~hnes~ coefficients were estimated from field reconnaissance and evaluation of photographs taken during that reconnaissance. Selected channel "n" values ranged from .03 to .045 through the ohannel and .035 to .10 along the overbanks. A summary of "n" values along with selected photographs to document chosen values is contained in the Technical Addendum. The HEC-2 water surface profiles through bridges and culverts were checked by hand calculations_ The hand calculations ."ere deemed more reliable for four bridges, and consequently these hand calculated elevations were input into the model data upstrenm of the affected bridges. crossings evaluated in this manner ~cre the C & S Railroad bridge, the Stover Street hr.-idge. the Stu",.t street bridge and the openings through the BNRR embankment. The 100-year event, flooded drea~ and floodway for developed conditions with the existing Chilnnel arc ::;hown on Pliltes 1 through 15. These plates also illustrate channel stationi.ng and cross section orientation. Water surface profiles for the 2-. 10-, 25- , 50-, 100-, and 500-year floods for developed conditions with the existing ch:lnncl arc presented on Plates 1', throu'Jh 2? Th",,;;p plates also identify crQO;S se..:tiQIl locations, ch<lnnel bottom elevation, and bridge and road locations. '1'~lC 100-y"'''- floodplain with chilnncl improv~mcnts lS identiiied on the Recommende-d Improv8mcnts Preliminary De~ign (Pl<ltes 28-35). " "