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<br />The results obtained from the curves for areas measuring <br />less than 10 square miles: were coordinated and adjusted <br />to be consistent with the' hydrologic data obtained from <br />the Soil Conservation ~ervice for the two dams on <br />Carbon Arroyo and Fishers Peak Arroyo, adjacent to the <br />study area. <br /> <br />Peak flows derived for areas measuring over 10 square <br />miles were compared with those obtained by using the <br />U.S. Geological Survey equations from the Manual for <br />Estimating Flood Characteristics of Natural-Flow <br />Streams in Colorado (Reference 4). They compared <br />favorably; based on this comparison, it was decided not <br />to adjust the tributary profiles to correspond exactly <br />with the U.S. Geological Survey procedure. For the <br />Purgatoire River, the difference between the U.S. Army <br />Corps of Engineers method and the U.S. Geological <br />Survey procedure was significant. Therefore, adjust- <br />ments were made by Gingery & Associates, Inc. using the <br />U.S. Army Corps of Engineers hydraulic computer model <br />and inserting the new flo~ data. The profiles were <br />then adjusted to reflect the new data. <br /> <br />. <br /> <br />Figure 4 shows the relationship of peak discharge to <br />the drainage area for the' 10-, 50-, 100-, and 500-year <br />floods for the streams studied in detail. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic, characteristics of streams in <br />the community are carried out to provide estimates of <br />the elevations of floods of the selected recurrence <br />intervals along each stream studied in detail. Water- <br />surface profiles, reaches, and flooded areas were deter- <br />mined by using the U. S. Army Corps of Engineers' HEC-2 <br />Computer Program (Reference 5) in conjunction with field <br />surveys. Allowance was made for obstructive effects of <br />flood-borne debris and existing flood plain encroachments, <br />such as homes, businesses~ and bridges. The Purgatoire <br />River flow is primarily ih the unstable range, undulating <br />from subcritical to super9ritical flow. Tributaries were <br />within. the supercritical flow range with true backwater <br />conditions being established only for short distances <br />above obstructions, such as bridges. Critical depths <br />were assumed elsewhere. Computed water-surface profiles <br />drawn to an accuracy of 0.5 foot are shown on Panels OlP <br />through 09P (Exhibit 1). ' <br /> <br />All elevations are refere~ced to the National Geodetic <br />Vertical Datum of 1929 (N9VD). Elevation reference marks <br />are shown on the maps. <br /> <br />8 <br />