Laserfiche WebLink
<br />5 <br /> <br />Figure 1 shows the major planimetric features of the study area. The <br />channel above 31st Street has a bottom width varying from 15 to 25 feet wide, <br />and is typically overgrown with trees and shrubs. The roughness values of the <br />stream vary from .04 to .07, with overbank roughnesses varying between .020 to <br />.045. The stream was diverted to accomodate a water intake structure, owned <br />by the City of Colorado Springs, approximately 2,000 feet upstream of 31st <br />Street. The area adjacent to the diversion (the Red Rock Canyon Mobile Home <br />Park) would be overtopped during a 10-year or greater flood event. Upstream <br />of the diversion, the stream is heavily overgrown. <br />The 100-year floodway is typically 500-feet or wider upstream of 31st <br />Street, which is the result of the overtopping of 31st, and the limited chan- <br />nel carrying capacity of this portion of Fountain Creek. The 100-year flow of <br />19,600 cubic feet per second cannot be narrowed and stay within FEMA criteria <br />without enlarging the 31st Bridge and improving the Fountain Creek channel. <br />Should these types of improvements be constructed, the floodway could be <br />narrowed within the Red Rock Canyon Shopping Center area, the area proposed <br />for additional improvements, and additional land area adjacent thereto <br />included in the scope of this study. The economic feasibility is positive, as <br />is the damage reduction notwithstanding the public health and safety benefits. <br /> <br />Alternative Evaluation <br />Several combinations of bridge and channel improvements were evaluated <br />during the hydraulic analysis. Common to all alternatives was the assumption <br />that a small private bridge downstream of 31st Street would be removed during <br />a 10~year or greater event, and the diversion structure adjacent to the Red <br />Rock Canyon Mobile Home Park be eliminated or redesigned by the City of <br />Colorado Springs. Each alternative was hydraulically modeled to assess each <br />design's impact on overbank flooding damages, while limiting construction <br />costs. <br />Shown in Table 1 is a summary of the alternitive hydraulic analysis. <br />The area evaluated is shown on Figure 2, showing the stream cross-sections uti- <br />lized in the hydraulic analysis. The 10-, 50-, 100- and 500-year flood plain, <br />and the 100-year floodway, limits are also shown on Figure 2. Table 2 pre- <br />sents a qualitative analysis of each alternative. <br />