What do the diagonal lines on the new format FIRM indicate?

The diagonal lines on the new format Flood Insurance Rate Map (FIRM) specifically indicate floodway areas. Floodways are defined as the channel of a river or stream and the adjacent land areas that must be reserved to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height. This designation is crucial for floodplain management and helps determine where development should be restricted to minimize flood risk and preserve the natural flow of water.

Understanding the importance of floodway areas is essential for effective floodplain management, as these areas are critical for maintaining the functionality of the floodplain. When mapping these regions, it is vital to communicate clearly where development should be limited to avoid unwanted impacts on flood risks and to protect surrounding communities.