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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Flood Velocities <br /> <br />- SUMMARY - <br /> <br />Mean velocities in the floodway generally range between two and five feet <br />per second (fps) with flow velocities in the channel exceeding ten fps <br />at certain locations. Velocities in the overbank typically range between <br />zero and four fps. <br /> <br />This report has identified the probable flooding limits of 100- and 500-year <br />flood events occurri ng on Lower Boul der Creek from Vall ey Vi ew Road to the <br />Boulder-Weld County Line. <br /> <br />Velocities in excess of six to eight fps can cause severe erosion of stream <br />banks, and are capable of transporting large rocks and debris. Velocities <br />in this range can also erode fill around bridge abutments, causing possible <br />bridge failure. Lower velocities of approximately two fps or less will <br />deposit debris and silt. <br /> <br />The floodplain limits are based on hydrologic and hydraulic information <br />developed by the Omaha Oistrict Corps of Engineers. The flood profiles and <br />corresponding flood boundaries are based on existing floodplain conditions <br />as shown on the mapping. The flood profiles also reflect unobstructed <br />channel conditions and, therefore, do not account for potential blockage <br />problems typically associated with large debris. Floods of greater magnitude <br />can and will occur in which the limits of flooding will exceed those shown <br />in thi s report. <br /> <br />Presently there are areas along Lower Boulder Creek where flooding may result <br />in extensive flood damages. Regulation of future floodplain construction <br />activities will at least serve to limit increases in the flood damage potential <br />while any improvements will serve to minimize or reduce the potential for <br />fl ood damage. <br /> <br />12 <br />