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3.0 ENGINEERING METHODS For the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or SOO-year period (recurrence interval) have been selected as having special significance for flood plain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and SOO-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term averaqe period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood which equals or exceeds the 100-year flood (1 percent chance of annual exceedence) in any 50-year period is approximately 40 percent (4 in 10), and, for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periOdically to reflect future changes. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge- frequency relationships for each flooding source studied in detail affecting the community. Data from the Cucharas River stream-gaging station at Boyd Ranch near La Veta were used to develop data for this study. The gage is located in Huerfano County, on the left bank at Boyd Ranch, 29 feet downstream from a private bridge, 1.4 miles downstream from the confluence with Chaparral Creek, and approximately 5.0 miles southwest of La Veta. It has been in operation since 1934 and records for 39 years were used. A discharge-frequency relationship for the Cucharas River was devel- oped from a frequency curve of peak flows that was constructed from available stream data. Regional frequency analyses were used to develop discharge-frequency relationships for Middle Creek. Peak discharge-drainage area relationships for the Cucharas River and Middle Creek are shown in Table 1. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the eleva- tions of floods of the selected recurrence intervals. 7