1997-06-13_REPORT - M1981302 (16)

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' modeled from the current Reclamation Grading Plan. A second hydraulic model, Condition 2, was generated with the assumption that the berm surrounding the property ' could be certified by FEMA as a flood protection levee. This model was entitled "100- Year Floodplain with Certified Flood Levee". These hydraulic models are provided in the Technical Appendix of this report. Both conditions analyze water surface elevations using the 100-year flood peak discharges provided in the FIS regulatory model. It is therefore assumed that flood peaks ` are not attenuated by floodplain or overbank storage. It is also assumed that the Viele Canal is flowing full and does not convey South Boulder Creek flood flows. ' Condition 1 - "100-Year Floodnlain Model - No Levee with 200-Foot Wide Channel: ' In order to analyze the first condition (no berm), which included the construction of a 200-foot wide (bottom width) interior interceptor channel, the mining operator's most current reclamation grading plan, which includes this channel, was utilized to supplement the G&O topography and current as-mined topographic conditions survey information. This Reclamation Grading Plan was prepared by Scott, Cox & Associates ' dated April, 1996. The field survey data was obtained in May, 1996. The Reclamation Grading Plan includes an approximately 200 foot wide interceptor channel along the interior southern and eastern edges of the Property to intercept spills from the South Boulder Creek main channel during the 100-year flood. The second condition assumed ' the site perimeter berm was constructed in accordance with FEMA criteria as a flood protection levee and could be certified as such. Additional mapping utilized for this ' model was obtained from the City of Boulder's May, 1993 aerial topography. ' For Condition 1, a portion of the South Boulder Creek 100-year flood waters enter the Flatiron Property along the southern property boundary and flow to the north within the interior interceptor channel toward U.S. Highway 36. The HEC-2 analysis indicates -14-