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<br />TABLE 2 <br />SOILS CLASSIFICA nONS <br /> <br />S.C.S Soils <br />Map Numberinl! <br /> <br />Soil Classificatio!l <br /> <br />H)'drologic <br />S(~LU:;roup <br /> <br />58 <br />59 <br />60 <br />61 <br />62 <br />63 <br />71 <br />92 <br /> <br />Limon <br />Limon <br />Limon <br />Limon <br />Limon <br />Limon <br />Midway <br />Riverwash <br /> <br />c <br /> <br />]) <br />]) <br /> <br />C <br />I~ <br /> <br />D <br />D <br />]) <br /> <br />F. Runoff Curve Numbers <br />Runoff Curve Numbers (CN's) were determined for the basin by utilizing soils and land use <br />information described in previous sections. Curve numbers for the undeveloped pOItions of the <br />basin were prepared based on projected land dcnsities with some agricultural land n:maining in its <br />existing rangeland conditions. <br /> <br />IV. HYDRAULIC DESIGN EVALUATION <br /> <br />A. Existing Structure Evaluation <br />Only the existing structures which transport flows out of major subbasins have been examined in <br />this report. These structures vary from a 12" CMP to 60" CMP. An allowable headwater of 6" <br />below the edge of pavement was utilized to calculate maximum culvert capacities. The existing <br />capacities of these structures were estimated using, primarily, inlet control analysis. <br /> <br />The analysis revealed that a portion of the existing structures throughout the basin are unable to <br />effectively handle the existing 25 year, 24-hour stOnTI. without overflowing the roadways. An <br />existing structure evaluation chart was developed 1.0 summarize these findings and is included at <br />the end of this section. <br /> <br />B. Existing Drainagewav Evaluation <br />As outlined in the Major Drainageway and Facilities section, most of the major drainage ways <br />within the Orchard Avenue drainage basin are natural, unimproved channels. In the upper reaches <br />of the basin, the channels are typically wide, grassed swalcs with little or no signs of erosion. The <br />existing capacities of major channel reaches widlin the basin were estimated using normal depth <br />flow analysis. <br /> <br />C. Environmental Inventory <br />The only significant environmentally sensitive area within the Orchard Avenue II.:!.sin is the <br />wetland pond adjacent to the Arkansas River as dl:SCI;.bed in the Existing Surface Water <br />Improvements Section. <br />