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FLOOD10503
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Last modified
1/26/2010 10:13:28 AM
Creation date
10/30/2007 10:56:21 AM
Metadata
Fields
Template:
Floodplain Documents
County
Otero
Community
La Junta
Basin
Arkansas
Title
La Junta Flood Documents
Floodplain - Doc Type
Correspondence
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<br />_? <br /> <br />.' <br /> <br />Table 1 - Summary of Discharges <br /> <br /> Drainage Area Peak Discharge (cfs) <br />Flood Source and Location ( sq. mi.) ~O-year 50-year lOa-year 500-year <br />Arkansas River <br />at La Junta 12,210 28,000 68,000 92,000 156,200 <br />King Arroyo <br />at La Junta 25 1,550 5,000 7,500 17,000 <br />Anderson Arroyo <br />at La Junta 54 2,225 7,000 10,500 23,000 <br />3.2 Hydrau1 ic Analyses <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 el evations for fl oods <br />of the ~e1ected' recurrence intervals. <br /> <br />Water surface e1 evati ons for the 10-, 50-, 100- and 500-year fl oods <br />for the Arkansas River, Anderson Arroyo and King Arroyo, were <br />checked usi ng the Corps of Engineers HEC-2 Water Surface Profi 1 es <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 />structura 1 geometry. As a resul t of the rev i ew by the study <br />contractor, it was determined that the Corps of Engineers hydraulic <br />analysis should be used for the Flood Insurance Study for the City <br />of La Junta. <br /> <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 />f100dway 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 aerial photography was used to determine the <br />1 imits of each roughness zone. Roughness val ues 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 wa ter- surface <br />elevations to an accuracy of 0.5 foot for floods of the selected <br />recurrence intervals. <br /> <br />The f1 ood profil es presented' in thi s study are based on the effects <br />of flow through unobstructed hydrau1 ic structures and area, thus, <br />considered valid only if these structures do not fail and remain <br />unobstructed. Starti ng water surface el evati ons for each stream <br />were based on known water surface elevations. <br /> <br />8 <br /> <br />I <br />( <br />i <br /> <br />
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