What is a floodplain?
The following terms are used to describe the 100-year floodplain.

(1) “Floodplain” means the areas subject to FEMA regulations, generally adjoining a stream or river that would be covered by floodwater of a base flood except for sheetflood areas that receive less than one foot of water per occurrence. The floodplain consists of a floodway and floodway fringe.
(2) “Floodway” means the channel of a stream or river and the adjacent overbank areas that must be reserved in order to discharge a base flood without cumulatively increasing the water surface elevation more than one-half foot.
(3) “Floodway fringe” means that portion of the floodplain outside the limits of the floodway.

The 100-year floodplain designation does not mean that a certain property will be flooded once every 100-hundred years. The 100-year floodplain designation actually means there is a one (1%) percent chance per year that a property will be flooded. In addition, a 100-year flood could take place more than once during a 100-year time frame or in consecutive years.

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?