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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Condition 2 - 100- Year FloodDlain Model - FEMA Certified Flood Protection <br />Levee: <br /> <br />Under Condition 2, the 100-Year Floodplain Model- FEMA Certified Flood Protection <br />Levee Condition, the loo-year flood flows along South Boulder Creek were confined to <br />the floodplain areas south and east of the levee. At U.S. 36, downstream of the levee, the <br />100-year floodplain expands to the west and eventually overflows onto U.S. 36. The <br />discharge for this overflow was calculated using a split flow analysis between Cross <br />Sections 22010 and 33020 in the main channel hydraulic model. The analysis assumed <br />the traffic median in the center of U.S. 36 acts as a barrier to the passage of flood flows. <br />The HEC-2 hydraulic model for the certified flood levee condition is found in the <br />Technical Appendix of this report. <br /> <br />To identify the hydraulic feasibility of the overflow and to determine the extent of the <br />floodplain south of U.S. 36 on the Flatiron Property, the flow path along U.S. 36 was <br />defined and modeled using HEC-2. Two distinct flow paths were identified. One path, <br />called the U.S. 36 Overflow, follows U.S. 36 to the west. The second, called the U.S. 36 <br />South Overflow, flows south of the on-ramp at U.S. 36, into the existing ponds on the <br />Flatiron Property, and eventually rejoins the U.S. 36 Overflow. Two HEC-2 models <br />were developed to model these two separate flow paths and are included in the Technical <br />Appendix to this Report. <br /> <br />Both overflow models are hydraulically connected downstream at Cross Sections 90, <br />100, and 1l0, and upstream at Cross Sections 150 and 160. The flow regime at Cross <br />Section 90 was assumed to flow at critical because of the steep drop in elevation <br />immediately downstream. <br /> <br />The flow paths along both overflow channels were examined for potential off-site spill <br />areas. The discharge along the U.S. 36 South Overflow transported the overflow <br />discharge with no offsite spill areas. However, discharge along the U.S. 36 Overflow <br /> <br />-17- <br />