2011-06-30_REVISION - M1981302 (12)

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Flood Control Levee August 24, 1999 Page We interpret this condition to mean that the County would not change its official flood plain snap to reflect the proposed levee, but would wait to see the results ofthe anticipated USAGE flood study for South Boulder Creek. The USAGE eventually completed the hydrology and initiated the hydraulic evaluation (HEC-2 computations ) for that study. The hydraulic analysis, flood plain maps and flood profiles were completed by G&O and published in its report in July 19 8 6. The levee and channel had been constructed prior to the study, and were recognized as "effective" in the final flood plain delineation. The G&O flood Main was adopted by the Urban Drainage and Flood Control District, Boulder County, the State of Colorado, and F1IA. Therefore, this condition was satisfied by 1988. It is believed that the flood plain was also separately adopted by the City of Boulder. "'2. Ifthe areaprotected by the levee is to be considei-edfor r l n r fi•om thefloodplain ill the fitture, the applicant woad be responsible for m i17 g the pl-oposed or consh-zleted levee to n7eet the requirements of the Coips ofEngineers study. " We interpret this condition to mean that Flatiron Sand and Gravel Company would be responsible for raising or strengthening the levee or meeting any other applicable criteria) if it was required by the federal authority with jurisdiction to recognize the levee as an effective structure. The condition suggested that the USACE had that jurisdiction, but actually it was FENIA using criteria set by the USACE. The flood plain which was defined by G&O after the levee was constructed recognized the levee as an existing effective structure, and the flood plain limit was drawn as if the levee was a recognized structure. Later FMA adopted that flood plain as the 1 00-year base flood Main for South Boulder Creek. The applicable F1I criteria for recognizing levees (freeboard, stability, resistance to seepage, erosion protection, and maintenance) are evaluated in this report, which demonstrates that the Flatiron Sand and gravel Company has taken the necessary follow -up actions to comply with this condition. "'3. That all of the area disturbed vegetated slip native grasses of the ai-ea," This condition is being complied with as part of the reclamation plan for the gravel mi g operation. The flood plain which resulted from the hydraulic work (HEC-2 computer modeling ) begun by the USACE and completed by G&O recognizes the levee as an effective flood control measure. The flood plain limit intercepts and then follows the outside face of the flood control levee for approximately 4,100 feet before it again falls away from the levee. 1n the G&O study, the levee actually defines the limit for a total of 5,350 feet, including the upstream and downstream reaches of the levee. The flood plain was adopted and/or designated, and has since been ad�istered by the following entities: LEONARD RICE CONSULTING WATER ENGINEERS9 INC.