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I I I I I I I I I I I I I I I I I I 'I I Field Inspection. A field inspection of the basin was made on May 15, 1979. This inspection showed that all major canals crossing the basin, the Larimer and Weld Canal, the Terry Inlet, the Larimer County Canal, the poudre Valley Canal, and the North poudre Ditch, directly inter- cept flows from Dry Creek. Douglas Reservoir was also visited during this trip. The State Engineer's Office is currently requiring that certain improvements be made to this reservoir if its available storage is to be utilized. At this site, the spillway condition shows that it has obviously flowed in the past but the amount of erosion is not extensive, and therefore, outflows were probably moderate. The reservoir was built in the early 1900's. The field visit also turned up Park Creek Reservoir, an on-stream reservoir which was recently constructed, and therefore does not show up on the U.S.G.S. quadrangles. This reservoir was added to our maps using available aerial photography. Past Studies. Past hydrologic studies in the Dry Creek Basin include the analysis completed as part of the Fort Collins and Larimer County Flood Insurance Studies (References 3 and 4), and analyses of the Douglas Reservoir hydrology--one completed for the reservoir owner, and one completed as part of the State's Dam Safety Inspection Program (References 5 and 6). The Flood Insurance Study hydrology determined the frequency dis- charges for the 10-, 50-, 100-, and SOO-year events in a reach from the poudre River upstream to the U.S. Highway 287 crossing. The dis- charges determined in this analysis are shown in Table II. TABLE II FIS Hydrology Flood Event Discharge poudre River Confluence (cfs) U.S. 287 Crossing 10-Year 50-Year 100-Year SOO-Year 1610 2930 3480 5200 1190 2230 2650 4100 These discharges were determined using the SCS unit hydrograph method utilizing curve numbers. Rainfall was taken from the NOAA -s-