Flood Insurance Rate Map FAQs

What are Flood Insurance Rate Maps?

Flood Insurance Rate Maps (FIRMs) are published by FEMA to determine flood insurance requirements and to assist communities in regulating new development. Among other things, FIRMs show areas that have a 1% chance of flooding and a 0.2% chance of flooding in any given year (also known as the "100-year" and "500-year" floodplains). These areas are determined to be the areas of highest risk when a stream overflows its banks.

Why are All Flood Risks Not Shown

There may be other reasons for flooding in your neighborhood that are not shown on a FIRM, including:

• The actual rainfall amounts for a given storm event may exceed those assumed in the computation of mapped 100-year floodplain.
• Intense rainfalls can overwhelm local drainage systems - causing water to pond deeply in the streets or flow overland to the nearest stream, flooding homes along the way.
• Smaller channels may not have been studied by FEMA. The stream near your home may have a floodplain that is not shown on the maps. FEMA does not evaluate water bodies with drainage areas less than 1-square mile.

It is important to note that FIRMs are estimates using the best technology and engineering tools, but nature can be unpredictable. Nationwide, 1/3 of the flood loss claims are from property located outside of the mapped 1% (100-year) floodplain. Therefore, FEMA advises that even people outside of the mapped 100-year floodplain purchase flood insurance to protect their homes and guard against financial losses.

What’s on a Flood Insurance Rate Map?

FIRMs shows several things, but most importantly they shows the areas of highest flood potential along water bodies. Information provided on these maps includes:

• 1% annual chance or “100-year” floodplain (Zones AE, A, AO, and V);
• Base-flood elevations (elevation above mean sea level that the 1% annual flood reaches);
• 0.2% annual chance or “500-year” floodplain (Zone X);
• Floodway;
• Corporate limits (i.e. municipal boundaries);
• Streets and highways; and
• Engineering information, such as survey benchmarks and the location of cross sections used in computer simulations.

What do the Zones Mean?

The following table provides a summary of the different zones shown on the on the FIRMs for Winchester. The legend on the maps has a more detailed description of the zones.