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INVESTIGATIONS AND ANALYSIS A. Interpretation and Use of Report l. Frequency and Discharge: The la-year, 25-year, 50-year, and lOa-year flood events are used as the flood frequencies for this flood plain analysis. Thus, the data developed in this report will be suitable not only for regulation purposes and H.B. 1041 designation, but is also consistent with Federal Insurance Administration flood insurance studies conducted by the Federal Emergency Management Agency (FEMA). These 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 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: lO-ypar. 7.S-ypar and 50-ypar Flood Rvpnts 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 improvements, the location of parks and recreational facilities, agricultural lands, and appurtenant structures. The use of the lower frequency floods may be considered in planning flood prevention projects to protect agricultural areas, or other property where risk to life is not a factor. lOO-ypar Flood Rvpnt The lOa-year flood event may be used in lieu of lower frequencies for engineering design purposes where greater security from structure failure is desired. However, the most important use of the lOa-year flood event lies in flood plain management and land use planning as set forth in the state statutes. The State of Colorado and the Federal Government consider the lOa-year frequency flood as the flood event to be used in designing and protecting structures and dwellings for human occupation. Therefore, all flood plain regulations are based upon the lOa-year flood. 2. Flood Elevation: Water surface elevations for the la-year, 25-year, 50-year, and lOO-year floods, as determined at each cross- section, may be found in Tables 2(a) and (b) "Flood Frequency- Elevation and Discharge Data". The flood profile data (sheets lP- 22P) show a graphical relationship of water surface elevations along the stream reaches for the given frequencies. Selected typical cross-sections from different reaches within the study area are shown on sheets IX through 2X. The flood profiles may be used in areas where controversy arises over the lOa-year flood boundary shown on the Flood Plain Maps. Since the flood profile exhibits give the water surface elevation 6 I I I I I I I I I I I I I I I I I I I