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<br />i7 <br /> <br />" <br /> <br />. <br /> <br />. <br /> <br />Associates (TEA) reviewcd and revised all previous studies. The Corps' original hydrology <br />values werc dctermined to be acceptable, and therefore all floodplain analyses and re- <br />analyses used thc Corps' hydrology values. <br /> <br />. The existing FEMA Flood Insurance Study docs not providc floodplain mapping for the <br />Keewaydin subdivision, which is actually in the lOO-year floodplain. <br /> <br />. Bill Taggart, under contract with the Urban Drainage and Flood Control District, determined <br />that the hydraulic differences between his study, the G&O study, and the Love study are not <br />substantial. The main differences seem to bc in thc magnitudc of the split flows that occur at <br />thc Highway. In addition, the 500-year flow in the study area should really be largcr than <br />what thc G&O study shows. <br /> <br />. Bill DeGroot said that "phase I" of thc floodplain analysis by TEA is nearing completion. <br />Thcrc will be a "phase II" study by TEA that will address further hydraulic and other issues. <br /> <br />. Even if the levcc is certified, there is still a flood risk to downstream residents due to the 100- <br />year overflows into thc Keewaydin subdivision. However, the subdivision has better flood <br />protection with the levee than without it (assuming no levee failurc). <br /> <br />. Due to thc mining of thc property by the Flatirons company, thc floodplain and topography <br />has been substantially altered from the historic conditions. Approximately 4,000,000 cubic <br />yards of fill would be needed to fill in the "hole" left by thc mining activities. <br /> <br />. The topo mapping for a portion of the floodplain area upstrcam of Highway 36 is inadequate. <br />Ideally, new mapping (I' or 2' contours) would be needed to better analyze the floodplain. <br /> <br />Other comments and issues <br /> <br />. Boulder County is concerncd about the hydrology on South Boulder Creek. According to the <br />County, the peak flow values secm to be too low, and do not seem to bc proportional to the <br />Boulder Creek values. (The Corps of Engineers substantially increased the Boulder Creek <br />peak flows to help justify a proposed flood control project on Boulder Crcck a number of <br />years ago). Bill DeGroot said that re-evaluation of the hydrology at this late time would <br />substantially delay futurc master planning and floodplain study efforts. Larry Lang warned <br />thc County that peak flow values could possibly go down instead of up if the hydrology is rc- <br />evaluated. <br /> <br />. Larry Matel said that Boulder County is not interested in rushing through the levee <br />certification process. He also said that the County Commissioners will have to be educated <br />and brought up to speed on all of thc risks, options, and consequences of relevant levee <br />issues. The Commissioners will have to be convinced about "what's thc right thing to do" <br />before any dccisions are made. <br /> <br />3 <br />