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<br />Hvdraulics <br />The hydraulic analyses for this study were performed using normal depth calculations and <br />storm sewer capacity calculations. For the purposes of this study, all of the hydraulic <br />calculations and preliminary designs are based on a lO-year design event. <br /> <br />Existinf!. Holita Ditch <br />The typical channel geometry for the existing Holita Ditch reach from Russell Avenue to <br />Interstate 25 was estimated in the field. The bottom width of the channel is <br />approximately 4 feet, the depth is approximately 4 feet, and the side slopes are very steep <br />with an average slope of IH to IV. Some portions of the channel have nearly vertical <br />banks due to severe erosion. The channel is quite flat with an average longitudinal <br />channel slope of about 0.5 percent. The channel is in poor condition. Most of the <br />channel is choked with trees, shrubs, and debris. The ditch has a decreed total flow of 24 <br />cfs. The anticipated direct flow (irrigation) is about 6 cfs. The estimated ditch capacity <br />for the reach of interest (existing conditions) is 80 cfs. <br /> <br />Provosed Alternative 1 <br />The Holita Ditch capacity expansion proposed in alternative I consists of rehabilitating <br />3,700 linear feet of channel between Russell Avenue and Colorado Avenue. Plate I <br />presents a plan view that shows the location and affected reach for this alternative. The <br />capacity expansion would require excavation of the channel to enlarge the cross-section, <br />removal of existing vegetation and debris, and construction of a berm along the south <br />bank of the ditch. For the lO-year event, the total design flow equals 441 cfs (205 cfs <br />from the storm drain, 230 cfs from the additional watershed, and 6 cfs from the direct <br />irrigation flow). The proposed channel consists of an 8 foot bottom width, 2H to I V side <br />slopes, and minimum depth of 4.5 feet. The channel could have a gravel bottom with <br />grass-lined side slopes. Plate 2 presents the typical cross-section and hydraulic <br />characteristics of the proposed channel. <br /> <br />Provosed Alternative 2 <br />This alternative consists of a new RCP storm sewer which would begin at the existing <br />storm drain outfall (near intersection of Russell and Colorado Avenues) and continue <br />south to the Cucharas River. This alternative would consist of approximately 3,200 linear <br />feet of 54" diameter RCP storm sewer with manholes, and would require special <br />installation and casing under the railroad tracks. Plate 1 presents a plan view that shows <br />the location and affected reach for this alternative. Plate 3 shows the pipe cross-section, <br />diameter, and hydraulic characteristics. For the 10-year event, the total design flow <br />equals 205 cfs (flow from the existing storm drain only is assumed). <br /> <br />7 <br />