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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />HYDRAULIC ANALYSIS <br /> <br />Introduction: <br /> <br />Using the flood discharges as defined in the hydrologic analysis, water <br />surface profiles for Parachute Creek and the Colorado River were calculated with <br />the use of the U.S Army Corps of Engineers HEC2 computer program (ref. 3). The <br />Sacramento District of the Corps performed the HEC2 analysis of the Colorado <br />River and the SCS performed the original and revised calculations for Parachute <br />Creek. J. E. Langford and I\ssociates performed the revised 500-year flood <br />profile calculations for the overbank area of Parachute Creek in the Town. <br />Output listings for all runs are contained in a Technical Addendum on file with <br />the CWCB. <br /> <br />Cross sectional data was obtained from photogrammetric mapping of the area <br />provided by Analytical Surveys, Inc. (ref. 4). Field investigations for the <br />Parachute Creek analysis were originally performed by the SCS in 1982 and 1983. <br />These included measurements of bridges and verification of channel and overbank <br />roughness coefficients (Manning's "n" values). Field investigations inclUding <br />measurement of bridges were performed by the Corps for the Colorado River in <br />1985. <br /> <br />Additional measurements of the D&RG railroad bridge over Parachute Creek. <br />were obtained in 1986 by J. E. Langford and I\ssociates at the request of the <br />Town. The cross sectional area at the railroad bridge was found to be 367 <br />square feet, some 24% greater than the area used by the SCS in the original HEC2 <br />model for the bridge, see Figure 2. Additionally, cross sections 242 and 243 <br />were surveyed for the Town in 1986. These are plotted in Figure 3 together <br />with the SCS digitized cross-sections for comparison. The difference in the <br />railroad bridge area is the principal reason the Town requested the modification <br />to the SCS report. <br /> <br />Other factors that contribute to differences between the original SCS <br />hydraulic analysis and the revised analysis contained in this report are <br /> <br />10 <br />