How are floodplains (SFHA) illustrated on FIRMS?
The SFHA of each stream or river is visually depicted on a FIRM within two blue lines. There are three (3) categories of floodplain designation which may be included on each FIRM. Those three categories are:

Zone AE – This SFHA zone includes a visual portrayal of the floodway boundaries and the floodway fringe boundaries. Zone AE also includes the Base Flood Elevation (BFE) for different reaches of the stream or river. The locations of the BFE are illustrated with a wavy black line that runs perpendicular to the stream channel. The BFE is also shown near the wavy line. Zone AE boundaries were developed utilizing the three tools described above and are therefore the most accurate boundaries. In some cases, the floodway is the same width of the floodway fringe.

Zone A – The visual portrayal of Zone A boundaries does not include the boundary of a floodway as the floodway boundaries have not been determined within the visually depicted floodplain. In addition, the BFEs for the stream have not been calculated. As such, SFHA boundaries that are visually illustrated as Zone A are not as accurate as the Zone AE boundaries.

Zone AH – Zone AH is not regulated by B-SB as these areas are only susceptible to sheet flooding of less than one foot in depth.

Show All Answers

1. What is a floodplain?
2. What are official floodplain maps called?
3. What is the purpose of floodplain mapping?
4. How are floodplains mapped?
5. How are floodplains (SFHA) illustrated on FIRMS?
6. How much of Butte-Silver Bow is regulated by FIRMS?
7. Did the recently adopted FIRMs change the SHFA boundaries if the 1980s FIRMs?
8. Where can I review a paper copy of a FIRM?
9. How are floodplains regulated in Butte-Silver Bow?
10. What kind of development is permitted in with the SHFA?
11. How do I apply for a floodplain development permit?