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was plotted on an aerial photograph (Reference 5) of the Town of Nunn. The flood flows eroded the road embankment extensively around the concrete culvert under 4th street and caused minor basement flooding. 2.4 Flood Protection Measures No flood protection structures either exist or are proposed which would reduce the flood hazards in the Town of Nunn. 3.0 ENGINEERING METHODS For flooding sources studied in detail in the community, standard hydro- logic and hydraulic study methods were used to determine the flood hazard data required for this study. Floods having recurrence intervals of 10, 50, 100, and 500 years have been selected as having special significance for flood plain management and for flood insurance premium rates. The analyses reported here reflect current conditions in the watersheds of the flooding sources. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge- frequency relationships for floods of the selected recurrence intervals for each stream studied in detail in the community. No streamflow gages are located on Spring Creek Tributary. A search of records of existing gaged streams in Colorado indicated that there were no basins of similar size and physiographic charac- teristics or with recorded rainfall distributions from which compari- sons could be made for a model of the basin hydrology. Therefore, synthetic hyrograph analysis was used to develop storm discharges within the study area. Rainfall data and distribution used in the development of peak discharges for Spring Creek Tributary (both east and west flow paths) were obtained from the National Oceanic and Atmospheric Administration's atlas for Colorado (Reference 6). The data was rearranged following the criteria established in the Urban Storm Drainage Criteria Manual (Reference 7), which is characteristic of Colorado storms in the eastern portion of the State. The U.S. Soil Conservation Service Method, as described in the National Enqineerinq Handbook (Reference 8), was selected as the method which would best represent the runoff characteristics of the Spring Creek Tributary basin. Weighted average curve numbers were computed using soil and land use maps for Weld County (Reference 9). The time of concentra- tion was determined using stream hydraulics of approximate cross sections taken from U.S. Geological Survey topographic maps (Refer- ence 10). Discharges were computed for the 10- and lOa-year flood events and plotted on log-probability paper. The 50- and SOO-year discharges were obtained by straight-line extrapolation of the 10- and lOa-year values. 4