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<br />,. <br /> <br /><, <br /> <br />" <br /> <br />;. <br /> <br />,., <br /> <br />, . <br /> <br />Develop two-foot contour interv31, 1" = 100', oz:thophoto <br /> <br />Canyon Dam at HOl:"Setooth Reservoir to the Cache La Pouare River, <br />a distance of ilpproxilllately seven miles. Average slope of the <br />chilnnel thalweg through this reach is approximately one percent <br />(1\). Historically, the Spring Creek. Basin extended to the ."est, <br />through what is now Uorsetooth Reservoir, into the foothills. The <br />construction (from 1950-1954) of Horsetooth Reservoir, specifically <br />Spring Canyon Dam, isolated the upper reaches of the Basin, <br />effectively reducing the flood potential through Fort Collins. Tile <br />current drainage area inclUdes approximately 12 square miles, with <br />a mean basin elevation of approximately 5050 feet MSL. Figure 1 <br />locates the Spring Creek Basin. <br /> <br />mapping of the study reach. Supple",ent <br />field surveys of crossing structures. <br /> <br />this mapping with <br /> <br />L <br /> <br />Perform hydrologic analysis consisting <br />previously developed hydrologic computer <br />and fully developed conditions. <br /> <br />, <br /> <br />of modifying the <br />model for €xisting <br /> <br />Determine water surface profiles for the 2-yellr, 10-yellr, 25- <br />year, 50-year, 100-year and 500-year events for the fully <br />developed basin with existing channel conditions. <br /> <br />Develop and evaluate alternative improvements from College <br />Avenue to Arthur's Ditch. Evaluation to consist of a cost <br />benefit analysis of each alternative in addition to an <br />assessment of other factors such as public: acceptance and <br />environmental impact. Present the alternative evaluation to <br />the City for selection of a recommended alternative. <br /> <br />1.5 Flooding problems <br /> <br />Flooding of Spring Creek prior to the construction of Spring <br />Canyon Dam is well documented, with floods occurring in 1902, 1904, <br />19)8 and 1949. Rainfall intensities as high <I" 4.) inches during <br />a 24-hour period have' b"en recorded. 'l'he most d,llnuging flood <br />occurred 1n 19)8, when the road through Spring Canyon WaE' dc>stroyed <br />along with livestock downstream. <br /> <br />Develop flooded area maps of the study reach identifying the <br />100-year floodplain for the existing channel <:Ind th,,_ <br />recommended improvements with fully developed basin <br />conditions. In addition, delineate the lOO-year flond.",ay for <br />existing channel conditions. <br /> <br />Since the dam was completed, flooning adjacent to Spring Creek <br />has been of a les" severe nature. However, putential does exi:;t <br />for serious flooding, particularly within the i1rea between college <br />^venue lInd the Burlington Northern Haih.oild. The mobile home parks <br />located within this area currently are s\.bject to frequent, shallow <br />flooding. one of the most serious of these events occurred on Juno <br />25, 1983, after a storm whiCh produced d 1.9 inch rainfall over two <br />hour:j. 'rhe ::;tor:r. sewer whiCh carries Spring Cr""",k unl1<>r thf' Mobilf' <br />Home Pack "I.lrcharyed, "lid waler l'onued to a depth of several fect. <br />Property dilmage was il1 the $5,000 - $10.000 range. <br /> <br />Prepare the updated master plan document <br />wide improv."ments including supporting <br /> <br />identifying bilsin <br />hydrologic dati), <br /> <br />discharge profiles, water surface profiles, flo(ld."d area map5, <br />ilnrl text describing the methodology llsed in the study. <br /> <br />Basin Description <br /> <br />The Spring Creek Basin is located in th" south c,,"ntrCll rortion <br />of the city of f'ort Collins and traverses the City in the e""t-west <br />direction. The bas.in drains from west to e::lst beginn.ing at Spring <br /> <br />, <br /> <br />2 <br />