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INTERPRETATION AND USE OF ~EPORT DATA SOD-Year FloOd Event - The SOD-year flood event is useful in ma~ing the public aware that floods larger than the 100-year flood can and do occur. Just because a person is living above the 100-year flood boundary does not mean that he is completely safe from flooding. The SOO-year flood event can also be used for regulating high risk developments within the floodplain. Flood Frequency and Discharge The 10., 50-, 100-, and SOD-year flood events were used as the flood frequencies for this floodplain analysis. Thus the data developed in this report will be compatible not only for regulation purposes andH.B.1041 designations but also for Federal Insurance Administration flood insurance rate studies. 10-Year and 50-Year Flood Events Tables Sand 6 list the discharges and water surface elevations for the 10-, SO- 100- and SOO-year flood events at selected reference points. Flooded Areas The 1D0-year frequency flood has been selected by the State of Colorado as the fl.ood event to be used for floodplain delineation andregulat ion. The Flooded Area plates show the boundary of the 100- and SOO-year floodplains. Since the base map for the Flooded Area plates Is a 5' contour map, the outlines of the other flood events, 10-and50.year,cannotbe, in some areas, readily plotted using the information in Tables 5 and 6. The area delineated on the Flooded Area plates as the 100-year floodplain meets the requirements of H.B. 1041 as an area of state interest. Also upon official appro~al of this report by the Colorado ~ater Conservation Board the area outlined by the lOO-year flood boundary will be designated a floodplain area and may be regulated accordingly by the local officials. These various flood events have an a~erage occurrence of once in the number of years as indicated. For example, the 100-year flood occurs, on the average, once in a 100 year period, and has a one percent chance of being equaled or exceeded in any given year. The particular uses for the various flood events in addition to those stated above are as follows: Information regarding these lower frequency floods is especially useful for future engineering studies and land use planning purposes related to minor road systems, minor channel lmpro~ements, the location of parkS and recreational facil1ties, agricultural lands. and appurtenant structures. Forstructuresdnd uses of this type on the smaller tributaries and in areas y;here the hig hriskof structural failure is economically feasible and the hazard to life and property nonexistent, the use of the lower frequency floods may be considered. 100-Year Flood Event Cue to tne 5-fcct contclJ~ intc~val the~e ~ay be areas included within tne lOQ-year floodplain which are above the 100-year water surface elevation. Flood Elevations Water surface elevations for the 10-. 50-. 100~ arld SOO-year floods can be found in four different locations in this report. These locations include: (1) The flood frequency-elevation and discharge data presented in Tables Sand ? f0r select",1j points ~ long thp. rivf'r reaches: (2) the 1 imits of the 100- and 500-yearfloods in pldn presented in Plates 3 through 8; (3) the flood profiles are shown in Plates 9 through IS; (4) and Plates 16 through 24 showth ewatersurface elevation for different frequencies at typical cross sections throughout the study reach. The IOO-year flood event may also be used for engineering design purposes where a lower risk of failure than the 10- or 50-year flood is desired. Howe~er, t~e ~cst impcrtJ~t use of the lOO-year flood event !je~ in floodplain designatior and land use regulation as set forth in the state statutes. TheStateofCo!orado considers the 100-year frequency flood as the flood event to be used in designing and protecting structures and dwellings for human occupation. Therefore,all floodplainregulatiOnsarebaseduponthe100-yearflooc!. AIso,theareawhich \oIould be inundated by the 100.year floodlflay bedelineate(j as dna r.;oa of state interestassetforthinH.6.1041-thestdte'slanduse:Jill. The Flood Profiles may be used in areas wnere controversy arises over the ,DO-year flood boundary on the Flooded Area ~Iates. Since the Flood Profile plates give the elevations and distance or stationing from a known pOInt the high water elevations can be surveyed on the ground to alleviate any discrepancies on the base mo.p. 2' 25