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9.0 REVISIONS DESCRIPTION This section has been added to provlde information regarding significant revisions made since the original Flood Insurance Study was printed. Future revisions may be made that do not result in the republishing of the Flood Insurance Study report. To assure that any user is aware of all revisions, it is advisable to contact the community repository of flood-hazard data located at the City Clerk' 5 Office, One Des Combes Drive, Broomfield, Colorado 80038. 9.1 First Revision This study was revised on September 28, 1990, to incorporate the effects of revised hydrologic and hydraulic analyses along Nissen Reservoir Channel, also known as Broomfield Basin 3207. These analyses, performed by Sellards and Crigg, Inc. (S&G) of Lakewood, Colorado, model the effects of two detention ponds (identified as Ponds 6 and 7), constructed in 1988 between Ash Street and 10th Avenue, and channel improvements made to Nissen Reservoir Channel between Midway Boulevard and Birch Street. The hydrologic analysis was performed for this reViSion using the Urban Drainage and Flood Control District IS (UDFCD' s) Storm Water Management Model - PC Version (UDSWM2-PC). As a result of the construction of Detention Ponds 6 and 7, peak discharges for Nissen Reservoir Channel have decreased. The revised hydraulic analyses were performed using the Corps of Engineera HEC-2 step-backwater computer program. Flood Profiles were produced from the HEC-2, and, as a result, changes were made to the 100- and SOO-year floodplains and 100-year floodway as shown on Flood Insurance Rate Map (FIRM) and Flood Boundary and Floodway Map Panel 0220. Topographic maps at a scale of 1:2,400 and a contour interval of 2 feet, produced by the UDFCD and revised by S&G in November 1988, were used to produce the new boundaries. At the request of the City of Broomfield, the 100-year floodway between Birch Street and 10th Avenue was defined as being coincident with the 100-year floOdplain. This measure was taken in order to prevent any future development, specifically around Ponds 6 and 7, which would adversely affect the floodplain downstream of the revised area. The Summary of Profiles have reanalyses. Di scharges Table, been revised to Floodway Data Table, and Flood reflect the effects of the This revision also incorporated a Letter of Map Revision (LOMR) issued for the City of Broomfield on November 17, 1988. The LOMa revised a portion of the Nissen Reservoir Channel between Sheridan Boulevard and Midway Boulevard, and the Broomfield Reservoir Tributary, also shown on FIRM Panel 0220. The basis of the LOMR was a channelization project along both streams. In support of the LOMa request, a certified engineering report entitled "Highland Park South Filing No. 2 Letter of Map Revision," prepared by 32