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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 />floods have an average occurrence of once in the number of years as <br /> <br />indicated. For example, the 100-year frequency flood occurs once in 100 <br />years on the average, and has a one percent chance of being equaled or <br /> <br />exceeded in any given year. <br /> <br />Cottonwood Creek continues in a northeasterly direction carrying the <br /> <br /> <br />remaining flow which is nearly the same for all discharge-frequency <br /> <br /> <br />values equal to or greater than the channel capacity, approximately 600 <br /> <br /> <br />c.f.s. For example, the difference in discharge values between the 100- <br /> <br /> <br />year and 10-year flood is only 20 c.f.s. (600-580~20) at cross section <br /> <br /> <br />BO in Reach #2 (Table 1, page 7). At the next cross section BP, a short <br /> <br /> <br />distance upstream, the 100-year flood discharge is 1,300 c.f,s. About <br /> <br /> <br />700 c.f.s. is carried by the secondary channels and flood plain, and 600 <br /> <br /> <br />c.f.s. in the Cottonwood Creek Channel. <br /> <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 />Output data from the computer programs were used in developing: the <br /> <br /> <br />flood profile drawings, flood outlines on the flood hazard maps, and the <br /> <br /> <br />data for the flood frequency-elevation and discharge tables. <br /> <br />Flood outlines for the 100- and 500-year floods were located on flood <br />hazard area maps using water surface elevations, cross-section data, and <br />by interpolation between the cross-sections, The location of flood <br /> <br /> <br />lines at road crossings were computed using the normal openings of <br /> <br /> <br />bridges and culverts. Because of the multitude of possible events in <br /> <br /> <br />which sediment and debris could caUse blockage of bridges and culverts, <br /> <br /> <br />these considerations were not included in the study. It should be noted <br /> <br /> <br />that perched channel flow exists through much of the flood plain. This <br /> <br /> <br />is a higher secondary channel which receives inflow from some location <br /> <br /> <br />upstream and maintains a flatter slope than the primary channel. <br /> <br />Consequently, flood flows enter into Buena Vista by way of several <br />secondary channels in addition to Cottonwood Creek, <br /> <br />Soil Surveys <br /> <br />The Soil Survey for Chaffee-Lake Area (parts of Chaffee and Lake Counties) <br /> <br /> <br />was published by the USDA-Soil Conservation Service in October 1975. It <br /> <br /> <br />contains information that can be applied in managing farms, ranches, and <br /> <br /> <br />woodlands; in selecting sites for roads, ponds, .buildings, or other <br /> <br /> <br />structures; and in appraising the v~lue of tracts of land for agriculture, <br /> <br /> <br />industry, or recreation. Information regarding the soil surveys can be <br /> <br /> <br />obtained by contacting the Soil Conservation Service, 2490 West 26th <br /> <br /> <br />Avenue, Denver, Colorado 80217, or the Upper Arkansas SCD Field Office, <br /> <br /> <br />223 East Third Street, S-lida, Colorado 81201. <br /> <br />About 0.4 mile downstream from the North Fork confluence, out-of-bank <br /> <br /> <br />flows from Cottonwood Creek dump into an older channel and then spread <br /> <br /> <br />out across the flood plain, following several secondary channels in an <br /> <br /> <br />easterly direction. Flooding is shallow with flow depths averaging less <br /> <br /> <br />than 2 feet for the 100-year flood. A similar situation occurs about <br />0.5 mile further downstream from the first location. <br /> <br />C-5 <br /> <br />c-6 <br />