In a majority of cases, the recently adopted FIRMs did not alter SFHA boundaries for individual streams within Butte-Silver Bow. As such, if a new FIRM shows a property or structure within the SFHA it is very likely that the property or structure was in the SFHA on the FIRM developed in the 1980’s.
However, the SFHA boundaries on the new FIRMs were digitized by FEMA and then layered over aerial photographs of Butte-Silver Bow. As a result, it is much easier to establish whether a property or building is located within, or in close to proximity, to the SFHA. The adoption of the new FIRMs has resulted mortgage companies reevaluating the floodplain status of many properties within Butte-Silver Bow.
However, the Sand Creek floodplain, which runs south to north just to the west of Harrison Avenue, was significantly reduced north of Four Mile Road. A new flood study was undertaken at that time which incorporated the impact of the Sand Creek diversion that routes a significant portion of the Sand Creek stream flow through Bert Mooney Airport property. The adoption of a new SFHA for the diversion channel significantly reduced the amount of flood waters that would flow north of Four Mile Road. Consequently, the Sand Creek SFHA boundaries were significantly reduced on the new floodplain maps north of Four Mile Road.
New FIRMs were adopted for those portions of the Big Hole River adjacent to Butte-Silver Bow that were not previously regulated by FEMA approved floodplain maps. Prior to the adoption of the new FIRMs the only reach of the Big Hole River with FIRMs was from Melrose to just west of Divide. The adoption of the new FIRM’s in 2012 includes the entire stretch of the Big Hole River flowing adjacent to Butte-Silver Bow.
The visually depicted SFHA boundaries within the town of Melrose were greatly reduced with the adoption of the new FIRMs.