All of the counties, cities, and town have been working with the Federal Emergency Management Agency (FEMA) and Montana Department of Natural Resources and Conservation (DNRC) to update and produce new floodplain maps for the Big Horn, Yellowstone, and Tongue Rivers, Sarpy, and Tullock Creeks, several tributaries and all of the existing mapped floodplains in Rosebud County (see explanation in Rosebud County background section). This project will study and update 3,301 miles.
Updated floodplain maps will depict the latest, most accurate flood risk data, and will eventually result in updated FEMA floodplain maps. Most of the existing FEMA floodplain maps are based on data from the 1970s and 1980s. For more information on the floodplain mapping processes, see: Flood Study Process. For more information on the project areas and the background of the existing floodplain maps see below.
DNRC held project kick off meetings with the communities September 14-16, 2021
Big Horn/ City of Hardin/ Town of Lodge Grass September 14, 2021- to view the slides from that meeting click here
Treasure County September 15, 2021- to view the slides from that meeting click here
Yellowstone County September 15, 2021- to view the slides from that meeting click here
Rosebud County September 16, 2021- to view the slides from that meeting click here
Survey Work
Survey work is currently underway for the four counties. Data needed for this work include bathymetric survey data, and hydraulic structure survey data. Bathymetric survey data is collected in the water, either by wading or with a boat, to measure the depth of the river bottom. Structure survey data is collected with precise GPS instruments to measure the dimensions of bridges, culverts, and other structures. Some landowners in the project area may receive a letter about access from DNRC's contractor DOWL Engineering.
Click the button below to view survey locations and information.
The project study extents can be seen below.
Legend
Yellow= approximate floodplain Zone A (flood elevations will not be on the final floodplain maps. The county, city, and town will have flood elevations as supplemental information)
Orange= area with flood elevations Zone AE (flood elevation will be on the final floodplain maps).
History of floodplain maps
Big Horn County has had floodplain maps since 1978. The City of Hardin had a flood plan map that was issued in 1976, during the 1981 update the floodplain map was not reissued. The Town of Lodge Grass has had a floodplain map since 1975. During the 1981 update the town received a detailed flood study because of the devastating floods the town experienced during the 1978 floods. For Big Horn County and the City of Hardin they used the best information, they had at the time to map the areas they expected to get wet during a 1% annual chance (100-year) flood event. A flood study has never been done for the county or the city.
The project study extents can be seen below.
Legend
Yellow = approximate floodplain Zone A (flood elevations will not be on the final floodplain maps. The county, city, and town will have flood elevations as supplemental information)
Orange = area with flood elevations Zone AE (flood elevation will be on the final floodplain maps)
History of floodplain maps
Yellowstone County has never had floodplain maps, or a flood study done on the Big Horn River. In 1986 when Treasure County received their first floodplain maps FEMA issued maps on the Treasure County side of the Big Horn River but not on the Yellowstone County side.
The project study extents can be seen below.
Legend
Yellow= approximate floodplain Zone A (flood elevations will not be on the final floodplain maps. The county, city, and town will have flood elevations as supplemental information)
Orange= area with flood elevations Zone AE (flood elevation will be on the final floodplain maps).
History of floodplain maps
Treasure County received their first and only floodplain maps in 1986. A flood study was not completed for any part of the county prior to creating the maps. Treasure County has not had an update to the floodplain maps since they were issued.
The project extents can be seen below.
Legend
Yellow= approximate floodplain Zone A (flood elevations will not be on the final floodplain maps. The county will have the flood elevations as supplemental information)
Orange = area with flood elevations Zone AE (flood elevations will be on the final floodplain maps).
Floodplain Map History for Rosebud County
The City of Forsyth, Town of Colstrip and Rosebud all had floodplain maps issued in 1974. Then in 1978 Rosebud County had floodplain maps issued, the mapping was quite extensive and covered the entire county. In 1987 a request was made to remove the floodplain maps from the area’s that didn’t have development occurring and were more rural. In 1997 when the maps were converted to Flood Insurance Rate Maps FEMA 15 of the 57 floodplain maps were rescinded. Unfortunately, the rescinded maps were the ones that they county didn’t request. All of the Yellowstone River (except around Forsyth) Musselshell River, Tongue River, and Colstrip maps were rescinded. With the updated maps a new flood study was not conducted. The maps the county regulates to are from data that was collected in the 1970s.
Estimated Timeline
