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. The sCs-computed discharges on Boxelder Creek were based upon none of the proposed reservoirs being completed and all three proposed reservoirs above wellington being complete. At the time of this study, only two of the reservoirs had been constructed, so the assumed storage for the third structure (B-2) was eliminated based upon the information supplied by the SCS. . \ Discharges for Dry Creek were computed using the SWMM (Reference 12). The drainage basin was divided into 190 subbasins that drained into 139 channel sections. Basins were selected so that hydrographs would be available at critical design points, particularly at irri- gation canal crossings and at onstream reservoirs (Reference 1). Precipitation information was obtained from the National Oceanic and Atmospheric Administration Atlas (Reference 18). The 500-year rainfall, not available from the atlas, was extrapolated assuming a Gumbel probability distribution (Reference 1). Discharges for Fish Creek and the Fall River were computed based upon records of. stream gages located on the two streams. The Fish Creek gage has 30 years of record, and the Fall River gage has 9 years of record. These records were analyzed using a log-Pearson Type III distribution as recommended in u.s. Water Resources Council Bulletin 17 (Reference 11). These discharges were weighted with those obtained using regression equations from the Colorado Water Conservation Board's Technical Manual No.1 (Reference 10). Peak discharges for the 10-, 50-, and 100-year floods along the Cache La Poudre River were provided by the COE, omaha District (Reference 6). The 500-year discharges were estimated by straight line extrapolation of the 10-, 50-, and 100-year floods provided by the COE. The SWMM (Reference 12) was used to compute discharges for approxi- mate flooding on Boxelder Creek and Cooper Slough in the vicinity east of the City of Fort Collins (Reference 9). Peak discharge-drainage area relationships for streams studied in detail 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. ,. Cross sections for the Big Thompson River and its tributaries were taken from topographic maps at a scale of 1:2,400, with a contour interval of 2 feet (References 19, 20, and 21) and field surveys. These tributaries include the North Fork Big Thompson River, Big Thompson River Tributaries 1, 2, 3, and 4, Long Gulch, Rabbit Gulch, Quillan Gulch, West Creek, Fox Creek, Dark Gulch, Cedar Creek, 13 -