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<br />. <br /> <br />punlic that floods larger than the IOO-year flood can snd do OCcur. <br />The SOO-year flood can also be used to regulate high risk developments <br />in the flood plain, such as ouclear powerplanta or toxic material <br />scorage. <br /> <br />Tables 2 through 5 liat the discharges and water surface eleva- <br />tions for the 10-, 50-, 100-, snd 500-year flood events at selected <br />reference poInts. Plstes 5 through 9, SA through 9R, snd 10 through <br />21, show the area flooded by the lOO-yesr and 500-yesr floods under <br />existing conditions. Plates 22 through 39 show the streambed elevation <br />and water surface profiles for the 10-, 50-, 100-, and SOe-year floods <br />under existing conditions. <br /> <br />The flood boundaries wers located at each crosS section sod the <br />intervening flood boundaries woro dra~ based upon detailed topog~aphic <br />mapping, engin~e~ing judgment, and fleld observations. It is, however, <br />possible that mOre or less flooding should be shown on the flooded s~es <br />maps. Fo~ a specific aituation, ~e~e mo~C detailed accuracy is <br />required, the flood bounda~ies can be more accu~ately established by <br />determining the water surface elevation from the profile or reference <br />table snd then locating that elevation by survey on the flood plain. <br /> <br />Tables 6 through 9 ahow the effect of future basIn urbanization on <br />the discharge snd el~vation of the IOO-year flood. Plates 40 through <br />57 display water surface profiles for the 10o-year flood under existing <br />conditions compared with projected and total urbanization conditions. <br /> <br />The effett of the projected and total urbanization conditions on <br />flood cha~acteristics are similar. Undc~ either condition, there is <br />little increase in flooding on Fossil Creek downstream from the Union <br />P~cfflc ~~ilrosd, ss the embankment acts like a dsm. On Fossil Creek <br />upstream from the Union Pacific tailroad. flood depths typically <br />increase at various locations from about 0.2 fe~t to 2.0 feet. Fossil <br /> <br />. <br /> <br />Creek discha~ges increase from 30 to 60 pe~cent. On the three tribu- <br />taries atudied, flood depths generally Increase 2 feet or less with <br />urbanization. At a few locations on Fossil Creek and the tributaries, <br />flood depths could increase about 3 feet. Discharges on the t~ihu- <br />taries increaae up to about 50 percent. <br /> <br />. . <br /> <br />20 <br /> <br />21 <br />