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INTERPRETATIO~ AND "SE OF REPORT DATA Flood F~~q~en~y and Diachar~e The 10-, 50-, IOO-and500-ye"r flood eVents Io'ere used as the flood freqllenc1esforthisflood-plainanalysis. ThllS the data developed in this report will be compatible not only for regulation purposes. and H.B. 1041 designations, but also for Federal Insurance Administration flood insu~"nce rate atudies. The various flood events have an average occurrence of once in the number of years as indicated. For example, the lOa-year flood occurs, on the average, once in a lOa-year period, and has a 1 percent chance of being eq~lcd o~ excecded in any given yea~. laO-year Flood eVent The IOO-yea~ flood event may also be used for engineering design purposes where a lower risk of failure than the 10~ or 50-yea~ flood is desired. However, tho most importsnt use of the laO-year flood event lies in flood-plain designation snd Innd use regulstion as setfonhint he State statutes. The Stste of Colorado considers the lOO-y~ar fr"quency flood as the fl~od event t~ be uaed in designing and protecting structures and dwellings for human occupation. Therefore, all flood-plain regulations are based upon the lOO-year flood. Also, the area ",h1ch ",ould be inundated by the lOO-year fl~od may be delineated as an area of State intcrest as Set !orthinH.Il.I041--theStnte'slandusebill. SOo-year Flood event The SaG-year flood event is useful in making the public aware that floods larger than the laO-year flood Can and do occur. Just becauae a person is living above the lOO-year flood boundary does not oean that he is c0mpletcly ~afe fr~m flooding. The SOo-year flood event can also be used for re&ulll.tiag highrbk developlIlents within the flood plain such S6 nuelear po"'er plants. o~ the storage or manufacture of toxic or explosive materials. 15 RE:\OURCE: CON\UlT~NT\ INC Table S liata the discharges and "'''ter-surface elevations for the 10-, 50-, 100- and 50o-year flood events at sell'cted referen~e points. Flooded Areas The lOa-year frequency flood has been selected by the State of Colo- rsdo as the flood event to be used for flood-plain delineation and regula- tion. Thus the FlOOded Area plates sho,,' only the boundary of the lOO-yea~ flood plain. Since the base map for the Flooded Area plates is a 2-foot contour map, the outlines of the other flood events (SOO-year) can be readily plotted using the information in Table 5. I I I I I t I The area delineated On the Flooded A~ea plates as the lOa-year flood plain meets the requirements of H.B. 1041 as an area of State interest. Alao upon official approval of thia report by the Colorado Water Conserva- tion Board the area outlined by the lOa-year flood boundary ",ill be desig- nated a flOOd-plain area and may be regulated accordingly by the locsl officials. Flood Elevations Flood water surface elevations for the 10-, 50-, 100- and 500-year floods maybe found in four separate locations in this report. The flood frequency-elevation and disch,.rge data in Table 5 lists these elevstion~ at selected reference points. The Flooded Area Plates 2 through 10 give the plan view of the flooded area on a contour baae map and the high water elevations for the lOa-year flood can be interpolated frOlIlthis. The Hood Profile plates, Plates 5 through 11, show the streambed elevation and the high water elevations for all four frequency floods. Also the Cr~ss Section plates, Plates 14 to 17 show a graphical representation of the high water elevations at typical valley cross sections throughout the study reach. The Flo"d Pro!il".. ""'y he n~"rl In areas ",here controversy <lriscu Over the laO-year flood boulldary '''' tbe Flooded Area plates. Sinc" the Flood Frofile places give the elevations snd distance Or stationin~ fro~ a kno~~ point, the high water elevations can be surveyed on the ground to alleviate " RE:\OURC€ CON\UlT~NT\ INC