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<br />INTERPRETATION AND USE OF ~EPORT DATA <br /> <br />SOO-Year FloOd Event - <br />The SOO-year flood event is useful in ma~ing the public aware that floods <br />larger than the 100-year flood can and do occur. Just because a person is <br />living above the 100-year flood boundary does not mean that he is completely <br />safe from flooding. The SOO-year flood event can also be used for regulating <br />high risk developments within the floodplain. <br /> <br />Flood Frequency and Discharge <br />The 10., 50-, 100-, and SOO-year flood events were used as the flood <br />frequencies for this floodplain analysis. Thus the data de~eloped in this <br />report will be compatible not only for regulation purposes andH.B.1041 <br />designations but also for Federal Insurance Administration flood Insurance <br />rate studies. <br /> <br />10-Year and 50-Year Flood Events <br /> <br />Tables Sand 6 list the discharges and water surface elevations for the <br />10-, 50- 100- and SOO-year flood events at selected reference points. <br /> <br />Flooded Areas <br />The 100-year frequency flood has been selected by the State of Colorado <br />as the fl.ood event to be used for floodplain delineation andregulat ion. The <br />Flooded Area plates show the boundary of the 100- and SOO-year floodplains. <br />Since the base map for the FlOOded Area plates Is a 5' contour map, the outlines <br />of the other flood events, IQ-andSO.year,cannotbe, in some areas, readily <br />plotted using the information in Tables 5 and 6. <br /> <br />The area delineated on the Flooded Area plates as the 100-year floodplain <br />meets the requirements of H.B. 1041 as an area of state interest. Also upon <br />official approval of this report by the Colorado ~ater Conservation Board the <br />area outlined by the 100-year flood boundary will be designated a floodplain <br />area and may be regulated accordingly by the local officials. <br /> <br />These various flood events have an average occurrence of once in the <br />number of years as indicated. For example, the 100-year flood occurs, on <br />the average, once in a 100 year period, and has a one percent chance of <br />being equaled or exceeded in any given year. <br /> <br />The particular uses for the various flood e~ents in addition to those <br />stated above are as follows: <br /> <br />Information regarding these lower frequency floods is especially useful <br />for future engineering studies and land use planning purposes related to minor <br />road systems, minor channel Improvements, the location of parkS and recreational <br />facil1ties, agricultural lands, and appurtenant structures. Forstructuresdnd <br />uses of this type on the smaller tributaries and in areas ",here tne hi ghriskof <br />structural failure is economically feasible and the hazard to life and property <br />nonexistent, the use of the lower frequency floods may be considered. <br /> <br />100-Year Flood Event <br /> <br />Cue to the 5-fcct contc~~ intc~val the~e ~ay be areas included within th~ <br />lOQ-year floodplain which are above the 100-year water surface elevation. <br /> <br />Flood Elevations <br />Water surface elevations for the 10-, 50-, 100~ and SOD-year floods can be <br />found in four different locations in this report. These locations include: <br />(1) The flood frequency-elevation and discharge data presented in Tables 5 and <br />? f0r selected points ~ long thp. rivf'r reaches: (2) the I imits of the 100- and <br />SOD-year floods in plan presented in Plates 3 through 8; (3) the flood profiles <br />are shown in Plates 9 through IS; (4) and Plates 16 through 24 showt he water surface <br />elevation for different frequenCies at typical cross sections throughout the <br />study reach_ <br /> <br />The 100-year flood event may also be used for engineering design purposes <br />where a lower risk of failure than the 10- or 50-year flood is desired. However, <br /> <br />t~e ~cst important ~se of the 100-yea~ flood event lies in floodplain designation <br />and land use regulation as set forth in the state statutes. The State Of Colorado <br />considers the 100-year frequency flood as the flood event to be used in designing <br />and protecting structures and dwellings for human occupation. Therefore,all <br />floodplain regulations are based upon the 100-yea~ flood. Also, the area which <br />would be inundated by the 100.year flooolflay bedelineate(j as ana ro;oa of state <br />interestassetforthinH.6.1041-thestdte'slanduse:Jill. <br /> <br />The Flood Profiles may be used in areas where controversy a~i;es over the <br />,OO-year flood boundary on the Flooded Area plates. Since the Flood Profile <br />plates give the elevations and distance or stationing from a known pOInt the <br />high water elevations can be surveyed on the ground to alleviate any discrepancies <br />on the base rIldp. <br /> <br />2' <br /> <br />25 <br />