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Water-surface elevations of floods of the selected recurrence intervals on many of the streams studied by detailed methods were computed through use of the USACE HEC-2 step backwater computer program (Reference 46). Cross sections for the backwater analyses were field surveyed at selected locations. The hydraulic analyses for the flooding sources studied by approximate methods were based upon data derived fram the sources used to establish the peak discharges for these streams~ For all streams studied affecting water-surface elevations of floods intervals were computed using the computer program (Reference 46). the City of Boulder, the of the selected recurrence USACE HEC-2 step-backwater Cross sections used in the backwater analyses for the streams were developed photogrammetrically using aerial photography flown in October 1981 (Reference 47). All bridges, dams, and culverts were field surveyed to obtain elevation data and geometry. Roughness factors (Manning's "nil) used in the hydraulic computations for the detailed-study streams were chosen by engineering judgement and based on field ohservations of the flooding sources and floodplain areas. Roughness values for the main channel of the detailed-study streams ranged from 0.020 to 0.100; floodplain roughness values ranged fram 0.040 to 0.130. Starting water-surface elevations were dete~ned by the slope-area method, critical depth, or elevations at confluences if the timing of the peaks coincided. The hydraulic analyses for this study were based on partially obstructed flow, as defined by the City of Boulder and FEMA through field inspection. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. As a result of the detailed analysis, flooding along Twomile Canyon Creek was designated as areas of shallow flooding. The results obtained fram the HEC-2 computer model for James Creek, Little James Creek, and Unnamed Tributary to Little James Creek were verified by comparing them to ground photographs of the 1969 flood through Jamestown. Cross sections were obtained by field measurements. Bridges in this study were analyzed using a blockage criteria dependent upon bridge construction and water depth. Concrete and steel hridges were asswned unobstructed until the upstream water-surface elevation reached the bridge "low steeln elevation, at which time the bridge was assumed fully obstructed. Wooden bridge decks were assumed destroyed due to debris. This type of bridge was assumed unobstructed at all discharges with wingwal1s and abutments in 44