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I, '. --- '-' I Federal Emergency Management Agency Washington, o.c. 20472 NOV 26 1997 Mr. Chris Dropinski Acting City Manager City of Boulder P.O. Box 791 Boulder, Colorado 80306 Dear Mr. Dropinski: This responds to your letter -dated September 4, 1997, regarding the Flood Insurance Rate Map (FIRM) and Flood Insurance Study (FIS) report for Boulder County, Colorado and Incorporated Areas dated June 2, 1995. You stated that the City is aware of significant errors and omissions in the South Boulder Creek Flood Hazard Area Delineation (FHAD) study prepared by Greenhorne & O'Mara, Inc., dated July 1986. You requested that we suspend the use of the FHAD pending a detailed analysis and investigation of the accuracy and representations made by the study and that we revise the flood hazard information for South Boulder Creek shown on the effective FIRM and FIS report to reflect the conditions of the 1978 FIS and 1979 FIRM, which were based on a 1973 study by R.W. Beck and Associates. We appreciate the time you have taken to review the flood hazard information for South Boulder Creek and acknowledge your efforts to ensure the flood hazard information depicted on the effective FIRM is as accurate as possible. :i As you indicated, the Special Flood Hazard Area (SFHA) for South Boulder Creek shown on the effective FIRM is based on information developed in the FHAD study. The SFHA is the area that would be inundated by the flood having a I-percent chance of being equaled or exceeded in any given year (base flood). In Attachment D to your letter, entitled "Discussion on Mapping Errors and Omissions," you included information about a study performed by Love & Associates, Inc. (Love), dated August 12, 1996. Love concluded that the SFHA for South Boulder Creek in the vicinity of the Flatiron Property, upstream of U.S. Highway 36, is incorrect because the FHAD incorrectly modeled a man-made berm as either natural ground or a levee approved by the Federal Emergency Management Agency (FEMA). In your letter, you stated your concern that the upstream and downstream impacts of this berm never were analyzed. In addition, you stated that the Love study and a study performed by Taggart Engineering Associates, Inc. (Taggart), dated December 18, 1996, concluded that the model prepared for the FHAD does not accurately represent split flow from South Boulder Creek that spills to the north of the main channel downstream of the levee. You also stated your concern that the effects of the U.s. Highway 36 median crash barrier on the flood hazards in this area were not included in the FHAD.