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<br />Table 1 - Summary of Discharges <br /> <br />"nderson "rroyo <br />at La Junta <br /> <br />Drainage "rea Peak Discharae (cfs) <br />(sq, mi.) 10-year 50-year 10 -year SOD-year <br />12,210 28,000 68,000 92 ,000 156,200 <br />25 1,550 5,000 7,500 17,000 <br />54 2,225 7,000 10,500 23,000 <br /> <br />Flood Source and Location <br /> <br />/l.rkansas River <br />at La Junta <br /> <br />King "rroyo <br />at La Junta <br /> <br />3.2 Hydraulic "na1yses <br /> <br />Review of the Army Corp of Engineers hydraulic analysis (Reference <br />1) for the Arkansas River, Anderson Arroyo and King Arroyo were <br />carried out in order to check water surface elevations for floods <br />of the selected recurrence intervals. <br /> <br />Water surface el evations for the 10-, 50-, 100- and 500-year fl oods <br />for the Arkansas River, Anderson Arroyo and King Arroyo, were <br />checked using the Corps of Engineers HEC-2 Water Surface Profiles <br />Program, Cross sections for this analysis were obtained from <br />aerial topographic maps flown in March, 1976, coupled with <br />appropriate field verification (Reference 8). All bridges and <br />culverts were measured in the field to obtain elevation data and <br />structural geometry. As a result of the rev i ew by the study <br />contractor, it was determined that the Corps of Engineers hydraulic <br />anal ysi s shoul d be used for the Flood Insurance Study for the City <br />of La Junta. <br /> <br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles. For stream segments in which a <br />floodway was computed (Section 4.2), selected cross section <br />locations are shown on the Flood Boundary and Floodway Map. <br /> <br />Roughness factors (Mannings "n") were determined by field <br />inspection, Ground level photography aided in the selection of <br />roughness factors and aeri al photography wa s used to determi ne the <br />limits of each roughness zone. Roughness values for the study area <br />ranged from 0.038 to 0,040 in channels with overbank values ranging <br />from 0.032 to 0.085, for all recurrence intervals, <br /> <br />Flood profi 1 es were drawn showi ng the computed water- surface <br />elevations to an accuracy of 0.5 foot for floods of the selected <br />recurrence intervals. <br /> <br />The fl ood profil es presented in thi s study are based on the effects <br />of flow through unobstructed hydraulic structures and area, thus, <br />considered val id only if these structures do not fail and remain <br />unobstructed, Starti ng water surface el evations for each stream <br />were based on known water surface elevations. <br /> <br />8 <br />