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<br />INVESTIGATIONS AND ANALYSIS <br /> <br />A. Interpretation and Use of Report <br />1. Frequency and Discharge: The la-year, 25-year, 50-year, and <br />lOa-year flood events are used as the flood frequencies for this <br />flood plain analysis. Thus, the data developed in this report will <br />be suitable not only for regulation purposes and H.B. 1041 <br />designation, but is also consistent with Federal Insurance <br />Administration flood insurance studies conducted by the Federal <br />Emergency Management Agency (FEMA). <br /> <br />These various flood events have an average occurrence of once in <br />the number of years as indicated. For example, the lOa-year flood <br />occurs, on the average, once in a lOa-year period, and has a one <br />percent chance of being equaled or exceeded in any given year. <br /> <br />The particular uses for the various flood events in addition to <br />those stated above are as follows: <br /> <br />lO-ypar. 7.S-ypar and 50-ypar Flood Rvpnts <br /> <br />Information regarding these lower frequency floods is especially <br />useful for future engineering studies and land-use planning <br />purposes related to minor road systems, minor channel improvements, <br />the location of parks and recreational facilities, agricultural <br />lands, and appurtenant structures. The use of the lower frequency <br />floods may be considered in planning flood prevention projects to <br />protect agricultural areas, or other property where risk to life is <br />not a factor. <br /> <br />lOO-ypar Flood Rvpnt <br /> <br />The lOa-year flood event may be used in lieu of lower frequencies <br />for engineering design purposes where greater security from <br />structure failure is desired. However, the most important use of <br />the lOa-year flood event lies in flood plain management and land <br />use planning as set forth in the state statutes. The State of <br />Colorado and the Federal Government consider the lOa-year frequency <br />flood as the flood event to be used in designing and protecting <br />structures and dwellings for human occupation. Therefore, all <br />flood plain regulations are based upon the lOa-year flood. <br /> <br />2. Flood Elevation: Water surface elevations for the la-year, <br />25-year, 50-year, and 100-year floods, as determined at each cross- <br />section, may be found in Tables 2(a) and (b) "Flood Frequency- <br />Elevation and Discharge Data". The flood profile data (sheets 1P- <br />22P) show a graphical relationship of water surface elevations <br />along the stream reaches for the given frequencies. Selected <br />typical cross-sections from different reaches within the study area <br />are shown on sheets 1X through 2X. <br /> <br />The flood profiles may be used in areas where controversy arises <br />over the lOa-year flood boundary shown on the Flood Plain Maps. <br />Since the flood profile exhibits give the water surface elevation <br /> <br />6 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />