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<br />" <br />, <br /> <br />. <br /> <br />. <br /> <br />ATTACHMENT D <br />Discussion of Mapping Errors and Omissions <br />Greenhome & O'Mara South Boulder Creek Floodplain Study, 1986 <br /> <br />The City of Boulder has identified the following errors and omissions in the G&O South Boulder <br />Creek floodplain study that we believe warrant FEMA's reconsideration of the studies adoption <br />for local floodplain regulation. This discussion is based on City technical staff review and <br />analysis of the G&O study and recent studies completed by professional engineering consultants <br />in our area having expertise in floodplain analysis. The consultant studies include: <br /> <br />o Floodplain Analyses of South Boulder Creek at the Flatiron Properly in Boulder County. <br />Colorado, prepared for: University of Colorado at Boulder, prepared by Love & <br />Associates, Inc., August 12, 1996. <br /> <br />The Love & Associates (Love) study concluded that the FIS floodplain for South Boulder <br />Creek in the vicinity ofthe Flatiron Property (immediately upstream of U.S. 36) was <br />incorrect. G&O assumed that a berm surrounding the Flatiron Property gravel mine was <br />either natural ground or a FEMA approved flood protection levee, neither of which was <br />correct, thus causing much ofthe Flatiron Property to be removed from the 100,year <br />floodplain in error. <br /> <br />Love also concluded that the split flows from South Boulder Creek in the vicinity of the <br />Flatiron Property in the G&O model were incorrect. Love determined that an additional <br />1,000 cubic feet per second (cfs) of flood waters spill to the north and do not rejoin South <br />Boulder Creek north of U.S. 36 as reported in the G&O study. <br /> <br />o Evaluation of Certain Engineerinll" Studies of South Boulder Creek From Upstream of <br />Hiilhway 93 to Downstream of South Boulder Road Phase I, prepared for Urban <br />Drainage and Flood Control District, the City of Boulder, and the County of Boulder, <br />prepared by Taggart Engineering Associates, Inc., December 18, 1996. <br /> <br />Taggart Engineering Associates (Taggart) concluded that the G&O study should have <br />been expanded to include the South Boulder Creek split flows identified by Love, and <br />that the G&O study should have evaluated the spills leaving the creek in the vicinity of <br />the Flatirons property downstream to where the spills rejoin the creek. <br /> <br />Both consultant studies indicated that the G&O study was either incomplete or incorrect in <br />analyzing South Boulder Creek. <br /> <br />1. <br /> <br />Incomplete Study: The G&O study is incomplete and did not fully analyze the flood <br /> <br />., <br />