Floodplain maps are periodically updated and revised to reflect changing conditions, such as impacts of flooding, new topography, land development, updated mapping studies, and construction of floodplain improvements.
Floodplain map changes can take several forms:
The Flood Insurance Rate Map (FIRM) identifies areas in a community that are subject to flooding and shows the associated risks. One of the areas shown on a FIRM is a Special Flood Hazard Area (SFHA), or the 100-year floodplain. This area has a 1% or greater chance of flooding in any given year.
FEMA uses the most accurate flood hazard information available and applies rigorous standards while developing FIRMs. But, because of limitations of scale or topographic definition on the source maps, there may be elevated areas or "islands" that are not actually in the new regulatory floodplain shown on the maps. These island areas may appear relatively small on the FIRM and are sometimes included in the 100-year floodplain by nationwide floodplain map determination companies that prepare floodplain designations on behalf of the mortgage industry. Such cases are referred to as "inadvertent inclusions."
The City of Boulder will try to identify any inadvertent inclusions and let the property owners know of the Letter of Map Amendment (LOMA) processes and the "grandfather" provisions of the NFIP that may apply to them.