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, '" INVESTIGATIONS ~O ANALYSIS 8. Flood Elevation Internretatlon and Use of Recort Water surface elevations for the 10-, 25-, 50-, and IOO-year floods, as determined at each cross section, may be found in Table 4 "Flood Frequency-Elevation and Discharge Data". The flood profile data (sheets 1-13) 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 1 through 6. The flood profiles may be used in areas where controversy arises over the IOO-year flood boundary shown on the flood plain maps. since the flOOd profile exhibits give the water surface elevation at a specific point on the reference line, the flood elevations can be surveyed on the ground to alleviate any discrepancies on the base map. A. Freauencv and Discharae The 10-, 25-, 50-, and 100-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. These various flood events have an average occurrence of once in the number of years as indicated. For example, the lOO-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. C. Flooded Areas 10-vear. 25-vear and 50-vear Flood Events Flood plain maps, sheets 1 through 6, show the boundary of the 100-year flood plain. The flood plain boundary was plotted using flood contour elevations and stationing from the plotted flood profiles. This was done at elevation intervals compatible with the map contour intervals. Flood contours are shown as wiggly lines at 5 ft intervals perpendicular to the direction of flow. 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 planninq purposes related to minor road systems, minor c~annel ... 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 prp.vention projects to protect agricultural areas or other property where risk to life is not a factor. lOO-year Flood Event The lOO-year flood event may be used in lieu of lower frequencies for engineering design purposes "'~,ere greater security from structure failure is desired. However, the most important use of the loo-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 considers the lOO-year frequency flood as the flood event to be used in designing and proteoting structures and dwellings for human occupation. Therefore, all flood plain regulations are based upon the 100-year flood.