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,- 9 9 FUTURE FLOODS Only in rare instances has a stream experienced the lar- gest flood possible. Severe as the maximum known flood may have been on a given stream, it is generally accepted that a larger flood will occur. Larger floods have been experienced on streams with similar geographical and physiographical characteristics as the CUcharas River. Severe stoms will undoubtedly occur in the CUcharas watershed to cause future floods that will surpass known historic floods. Discussion of future floods in this report is limited primarily to those that have been designated as the 100- year flood and SOO-year flood, however, 10-year and 50-year flood data are presented. Definitions of these future floods are found in the Gloesary of Terms section of this ruport. Flood Magnitude and Their Frequencies Standard hydrologic and hydraulic methods were used to determine the magnitude of floods of the selected return frequen- cies. Hydrology data was developed from the results of a frequency analysis. Flow frequency parameters were developed from "Manual for Estimating Flood Characteristics of Natural-Flow Streams in Colo- rado." Peak discharges of the 10-, 50-, 100-, and SOO-year floods at selected locations along the Cucharas River are listed in Table 2. Floods larger than the SOO-year flood are possible, but the com- bination of factors necessary to produce such large flows would be extremely rare. The Corps of Engineers' HEC-2 slop-backwator com- puter program was used to develop the flooded areas and flood profiles. The 100-year frequency flood is defined as a flood having an average frequency of occurrence in the order of once in 100 years at a designated location, although it may occur in any year and pos- sibly in successive years. It can be expressed in terms of percen- tage to avoid the possible inference of regularity of occurrence. Thus, a flood with a 100-year recurrence interval would have a one 11