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<br />Table 1 - Summary of Discharges <br /> <br />Flood Source and Location <br /> <br />Ora i nage Area <br />(sq. mi.) 10-year <br /> <br />Peak Discharge (cfs) <br />50-year 100-year 500-year <br /> <br />Cottonwood Creek <br /> <br />At Gage <br />At Mouth <br /> <br />65 <br /> <br />570 <br /> <br />822 <br /> <br />936 <br />1,300 <br />3,930 <br /> <br />1,230 <br />1,710 <br /> <br />Arkansas River <br /> <br />105 <br />611 <br /> <br />800 <br />3,442 <br /> <br />1,140 <br /> <br />3,842 <br /> <br />4,102 <br /> <br />3.2 Hydraulic Analyses <br /> <br />The SCS hydraulic analysis (Reference 1) was performed using the WSP2 <br />Canputer Program (Technical Release No. 61, SCS, May 1976) (Reference <br />3). Review of the analysis for Cottonwood Creek was carried out by <br />COM in order to check water surface elevations for floods of the <br />selected recurrence intervals. <br /> <br />Water surface elevations for the 10-, 50-, 100- and 500-year floods <br />for Cottonwood Creek were checked using the Corps of Engineers HEC-2 <br />Water Surface Profile Program (Reference 4). Cross sections for this <br />analysis were obtained fran aerial survey flown November 6, 1975 <br />(Reference 5), coupled with appropriate field verification. All <br />bridges and culverts were measured in the field to obtain elevation <br />data and structural geometry. As a result of the review by the study <br />contractor, it was determined that the Soil Conservation Service <br />hydraulic analysis should be used for this Flood Insurance Study for <br />the Town of Buena Vi sta. <br /> <br />Locations of selected cross sections used in the hydraul ic analyses <br />are shown on the Flood Profi 1 es. For stream segments for whi ch a <br />f100dway is computed (Section 4.2), selected cross section locations <br />are also shown on the Flood Boundary and F100dway Map. <br /> <br />Roughness factors (Manni ng s "n" val ues) were determi ned by fi e1 d <br />inspection. Ground level photography aided in the selection of rough- <br />ness factors and aerial photography was used to determine the 1 imits <br />of each roughness zone. Typical roughness values for Cottonwood Creek <br />ranged from 0.045 to 0.110. <br /> <br />Flood profiles were drawn showing computed water-surface elevations to <br />an accuracy of 0.5 foot for floods of the selected recurrence inter- <br />val s. The fl ood profi1 es presented in thi s study are based on the <br />effects of flow through unobstructed hydrau1 ic structures and area, <br />thus, considered valid only if these structures do not fail and remain <br />unobstructed. The starting water surface elevation for Cottonwood <br /> <br />7 <br />