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<br />.' <br />. <br /> <br />. <br /> <br />. <br /> <br />impact study addressing the physical change and any upstream or downstream impacts <br />that resulted from the change. <br /> <br />3. Upstream and Downstream Impacts from the Berm were Never Analyzed: The G&O <br />study accepted the land form embankment around the mining operation upstream ofU,S, <br />36 as an existing land feature, and made no attempt to provide any background on the <br />berm, how this feature was approved, or how it impacted the floodplain based on historic <br />conditions. This berm obstructs and diverts the historic passage of floodwaters in the <br />South Boulder Creek floodplain, and increased flood elevations and velocities in this <br />stream reach. <br /> <br />This obstruction has an impact on flooding in the existing developed neighborhoods <br />within the City of Boulder, and should have been subject to a local review and approval <br />process to determine if the community was willing to accept any increased risks and <br />responsibility associated with a structural flood protection measure. <br /> <br />FEMA's regulations require an evaluation of upstream and downstream impacts as part <br />of any request to revise the floodplain based on physical changes and improvements. The <br />G&O study did not include such an analysis, and didn't report that floodplain elevations <br />and velocities were increased as a result ofthe berm construction. Nor did G&O detail <br />that the significant floodplain revision upstream of U.S. 36 was based on the creation of <br />the berm. <br /> <br />4. Levee Approval was Never Obtained: The G&O study was in error in assuming that <br />the earthen berm was natural ground providing an edge to the floodplain or a FEMA <br />approved flood protection levee. As a result of this assumption, G&O removed a large <br />area behind the berm from the regulatory floodplain without the due process and <br />regulatory permitting that is required for the approval of a major flood protection <br />structure impacting upstream or downstream lands, <br /> <br />The apparent defacto acceptance of the berm in the G&O study is exacerbated by gravel <br />mining operations that have occurred behind the berm since the floodplain was errantly <br />revised. The land behind the berm has been excavated to and remains at an elevation 12 ' <br />20 feet lower than the grades reflected in the G&O mapping. Because the gravel mine <br />was excavated into an alluvial deposit geologic formation, it did not create a pit that <br />would collect and confine flood waters. Instead, the excavated ground behind the berm <br />has a positive slope passing drainage away from the berm to the north. The lowered <br />elevation of the land behind the berm actually creates the potential to rapidly divert South <br />Boulder Creek floodwaters more directly into the City neighborhoods to the north. <br /> <br />No consideration of this outcome was ever represented to the City of Boulder or Boulder <br />County by the mining operator, and no public review for evaluating this increased flood <br />risk was ever presented. This issue should have been a vital component in the G&O <br />study. <br /> <br />iI <br />