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<br />Frequency <br /> <br />to cross flooded areas. Ingeneral,floodwaterthreeorrnorefeet <br />deep and flowing at 11 velocity of three or more teet per second <br />OOuldeaslly sweep an adult person ofl his teet, thuscreatlngdefl- <br />nlte danger of inJury or drowning. Rapidly rlslng;,nd swiftly flowing <br />floodwater may trap persons In homes that may be destroyed, or In <br />VtihiCles that are ultimately submerged or floated. Water Ilnesean <br />be ruptured by deposits of debris and the force of floodwater thus <br />creating theposslbTlityof contamTnateddomestTcwatersupplies. <br />Sanitary s"wer'!, btJCOtntl pressure lin"s, blowing ",..",hol" coVers to spew <br />r"wsewage Into the floodwaters, and stockyard waste adds tofhe <br />pollution and hazard of epidemic. <br />Water flowing In excess of four fe..t per second 15 cap- <br />ableot transporting sediment and causTng severe erosion of stream <br />banks and embankments around bridge abutrflflnts. The ~"turetT<">n ..ff..cts <br />of long.dur<ltlon flooding c"n we"ken bridge abutments, levees and <br />other embankments so they tail as the floodwaters recede. <br /> <br />StandaroProJectFloo<I <br />The Standard Project Flood 15 delined 1:15 a major flOOd <br />that can beexpeded to occur tror-a severe combination 01 rneteor- <br />ologlcal and hydrological condirlons that Is considered ~easonably <br />charactaristlcofthegeographicarea In which thB $tudy area is 10- <br />cated, excl~dlng ext~emely rare combTnatlons. The Co~ps of Engineers, <br />in cooperation with NOAA ~'eather Servi ce, has made cornprehens I 'Ie <br />studies and Investig<ltions based on file past reoords of experienced <br />storms and floods and has developed generalized procedures for esti- <br />mating the flood potential of storms. Severe as the maximum known <br />flood may have been on any glvens1"ream, It is generally accepted <br />that a larger flood wIll sooner or later occur. The magnTtude of <br />the Standard P~oje<;t and I nterrnodlate Reglona I Floods are shown in <br />Table 3. <br /> <br />The Intennedl"TeRegional Flood has, oydefTnltlon, an <br />average occur~ence f~equency of once In 100 years, or a 1% chance <br />01 bei ng <x:ualod or exceeded I fi any one ye~~ period. It is i mprac~ <br />tical. hOwever, to assign a frequency to the greater Standdrd Pro- <br />ject "'1000. For purposes of hazard ev~l u"tlon, It is Important to <br />recognize that either 01 these major floodS can occur in ~ny year. <br />Floods larger than the Standard Pmject Flood are possible, but the <br />comblnatlonoffac-torsnecessarytoproducesuch largetlowwould <br />rarely occur. <br /> <br />~0U I d create concl tlon~ haz,lrdous -:-0 p.,l.s,;.ns ar,c vec, :,c ies at7"mp7i ng <br /> <br />FlOOded Areas and FlOOd Demaqa <br />,~reas -:-hat will be f loodoc by the I nterClQdi "te Regional <br />ilnd Stanaar<:J Project Floods <lre Indicated On the flooced area maps <br />of Plate 2 filrough Plilte II. Reference liMS en the"", piates i~dl- <br />cate the elevation of tho IntermedTate Regional Flood aMd are shown <br />at five foot Intervals. By sub-:-recti~g fhe ground elevations <br />Irom the <lpproprlate reference elevation tho flood dopth ca~ ~e d~- <br />termi ned for any poi nT. These elevation ~eference lines ~ Iso repre- <br />sent the minlMu"n olMatlon for flOOd-proofing. FlOOd profiles on <br />P latos 12 through PI ate 21 i ndicat", the Alevatlons of both f IQ()rJ~ <br />e~C Cafi be used for Geterml n I ng f I 000 depth5 or f loodproof I fig e leva- <br />tloos. Typlcal cross sections on Plate 22 through Plate24are9 <br />~epresent"'ti ve secti ons from a~pro)(i mately /0 s.octl (ms Obtai nOd from <br />tiel d surv"'l's "nd photograoh ie fOOa~s. The location 01 all CrOSS <br />5iK,tlons are sho~'n em th{' profile ~y a heavy lir., 'lOd "um~(lr. <br />Floocwater depths d?Te~l~ed for any rartlt~lar cr05S ~ection are <br />'lot alwuys ind,{;atlve 01 t.'1e d.,~fhs uHain'ed. FlOOdwaters ir'eGue~'tly <br /> <br />Hazards of Large Floods <br />The extent and dd'",ge caused by .3ny flood dApends on <br />th8topogrcpnyoftheareafloodild, dspth and duratlOl1of flooding, <br />velocity of flow, r~te of rise, and developments in the flood plaTn. <br />An I nter1'"l!ldl ate Reglollal Flood on Cottonwood Cril'ek would result In <br />the I nundutlofl of resi dentT~ I anC corrmorcl<ll properties In the study <br />area. ~er tioodw.3tilr flowing at high v"locitv and car~ying aebrl~ <br /> <br />I') <br /> <br />iF> <br />