How are floodplains mapped?
Local governments that participate in the National Flood Insurance Program are issued FIRMs developed in cooperation with FEMA. In most instances, the floodplain profiles for individual streams or rivers are developed utilizing hydrologic and hydraulic studies and on-the-ground surveys. These three tools help determine the boundaries of the floodway and floodway fringe.

However, there may be floodplain profiles for other streams on a FIRM that were not developed utilizing hydrologic and hydraulic studies and on-the-ground surveys. As such, these floodplain profiles are not as accurate as floodplain profiles developed utilizing hydrologic and hydraulic studies and on-the-ground surveys. There are several streams in the Butte-Silver Bow jurisdictional area where the floodplain profiles were developed without FEMA utilizing these three tools.

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?