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<br />. <br /> <br />. <br /> <br />. <br /> <br />6.1.1 Floodplain Analyses and Results <br /> <br />On the effective workmap, the LINC DFP hydraulic baseline was drawn through the <br />middle of buildings. In the existing condition, the LINC DFP hydraulic baseline was adjusted <br />between 1 st Avenue and Lemay Avenue to more accurately reflect the primary conveyance path <br />betwel~n the buildings and Lincoln Avenue. Additionally, the LINC DFP hydraulic baseline was <br />extend north of Linden Street to convey Cache la Poudre River 500-year flows leaving the main <br />chmmel between Linden Street and the RN.R.R. Bridge (the Linden Spill). <br />Table 6.1 lists the cross section adjustments made between the corrected effective <br />condition and existing condition models. It should be noted that main chmmel cross section <br />adjustments (truncation of left over bank geometry) were located in areas not hydraulically <br />connected, during events equal to or less than the 100-year event, to the main chmmel. The left <br />bank geometry data of Cross Sections AR:227397, 227437, and AS:228117 were re-cut utilizing <br />the existing I-foot contour interval topography. The effective geometry for the Lincoln Avenue <br />to Linden Street left overbank spill (the Lincoln Spill) was updated in the existing condition <br />analysis. To determine the amount of 500-year flow leaving the main chmmel at the Linden <br />Spill, between Linden Street and the RN.R.R., a lateral weir was incorporated into the <br />EX500Q06 model. <br />A comparative summary of the corrected and existing discharge profiles is provided in <br />Appendix D.2. A summary of the existing condition water surface profiles is presented in Table <br />6.2. The Cache la Poudre River main chmmel existing condition 100-year discharges and water <br />surfac,e elevations decreased as a result of: (a) updating the geometry of Cross Section <br />AS:228117; and (b) updating the geometry of the Lincoln Spill. <br />The Cache la Poudre River main chmmel existing condition 500-year water surface <br />elevations increased between Cross Sections AP:224597 and AR:227397 as a result of the <br />assumption that 100% of the LINC DFP flows return to the Cache la Poudre River main chmmel <br />over Lincoln Avenue at Cross Section AQ:226167. The Cache la Poudre River main chmmel <br />existing condition 500-year water surface elevations decreased between Cross Sections 227437 <br />and 229757 as a result of adding the Linden Street Spill and updating the geometry of the <br />Lincoln Street Spill. The Linden Spill amounted to 2,602 cfs overtopping Linden Street during <br />the 500-year event. The effective 500-year Lincoln Avenue Spill from the main channel to the <br />LINe DFP occurred on the left over bank between Lincoln Avenue and Linden Street. The <br />effective 500-year Lincoln Spill of 3,572 cfs decreased to 3,125 cfs in the existing condition. <br />500-year flows remaining in the LINC DFP east of Lemay Avenue decreased from 433 cfs in the <br />corrected effective condition to 57 cfs in the existing condition, thereby affirming the analytical <br />assumption that 100% of the LINC DFP flows return to the main chmmel over Lincoln Avenue. <br />LINC DFP 100- and 500-year water surface elevations increased and decreased along the flow <br />path as a result of adding the Linden Spill, more detailed topography, and revisions to the <br />hydraulic baseline and cross sections. <br /> <br />COFC2003-l0 Oxbow FINAL LOMR.doc <br /> <br />6.2 <br /> <br />ANdERSON CONsulTiNG ENGiNEERS, INC. <br />