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F <br /> acknowledge that the 100- year floodplain downstream of U.S. Highway 36 has not been <br /> completely delineated by the existing floodplain studies. <br /> EXAMINATION OF THE DELINEATED FLOOD HAZARD/RISK <br /> Floodplain studies which date back to 1969 show that a portion of the Flatiron/ Gateway <br /> property lies within the limits of the South Boulder Creek 100- year Floodplain. Today's 100- <br /> year floodplain is based on the presence of an in-place levee system. The Love study presents <br /> an analysis with and without the Flatiron levee system. The engineering analyses show that the <br /> levee system reduces the downstream flood hazard. Recently, the owner of the levee system <br /> (Flatiron Gravel Company) was notified by FEMA that the levee system does not meet federal <br /> design and safety standards. The notification advised the owners and local and state officials <br /> thaf if the levee system is not improved to meet FEMA's levee standards, a new map will be <br /> issued which shows portions of the site and downstream areas subject to inundation from a 100- <br /> year flood event. <br /> Should the existing levee fail during a large event (100- year flood) the hazard to <br /> downstream areas could be worse than the pre-mining condition because the lands within the <br /> mined areas are up to 12 feet lower than pre-mining operation elevations. This changed <br /> condition could initiate a change in the direction of floodwaters during times of high flow and <br /> could inundate additional areas along the left overbank not presently in an identified 100- year <br /> floodplain. Due to this potential floodplain condition, it appears that it may be in the best <br /> interest of the community that the levee system become a permanent floodplain landform. <br /> Without the levee system, the Love investigations show that larger flood flows will be <br /> experienced at downstream floodplain locations. It should be noted that a delineated downstream <br /> floodplain may include numerous homes in the floodplain. The Board staff findings the Love's <br /> investigations to be a reasonable assessment of existing conditions. <br /> OVERVIEW OF THE FLOOD MITIGATION MEASURES <br /> With the recent development activities which have occurred upstream and downstream <br /> of U.S. Highway 36, there is a need for the implementation of flood mitigation measures for <br /> the South Boulder Creek floodplain risks. Some potential flood mitigation measures are: <br /> • Certification of the Flatiron Levee System - It appears to us that the community may <br /> want to endorse this mitigation measure. The action will assist to lessen the magnitude <br /> of the threat to downstream flood prone lands and property. The CWCB has made a <br /> request to FEMA not to change the flood insurance maps until after March 15, 1997. <br /> This will provide owners and the local communities to make the necessary levee system <br /> improvements to obtain FEMA levee certification prior to the 1997 flood season. I <br /> understand that FEMA is considering the request. The present Love investigation does <br /> not include the required technical data to fully evaluate the levee system for levee <br /> certification. <br /> 5 <br />