Clark Fork and Bitterroot Rivers Floodplain Remapping
The Clark Fork and Bitterroot Rivers floodplain remapping is still in process. Currently, draft maps are available for review. To see how the mapping update may affect your property, visit the map viewer here. The next step is FEMA approval of the draft maps. Once approved, they will become preliminary maps and the appeal period will begin. For more information on this project, see below.
The preliminary maps are expected to be available in May. At that point in time, the formal appear period will start.
Project Description
The Montana Department ofContinue reading
Clark Fork and Bitterroot Rivers Floodplain Remapping
The Clark Fork and Bitterroot Rivers floodplain remapping is still in process. Currently, draft maps are available for review. To see how the mapping update may affect your property, visit the map viewer here. The next step is FEMA approval of the draft maps. Once approved, they will become preliminary maps and the appeal period will begin. For more information on this project, see below.
The preliminary maps are expected to be available in May. At that point in time, the formal appear period will start.
Project Description
The Montana Department of Natural Resources & Conservation (DNRC), in conjunction with the Federal Emergency Management Agency (FEMA), recently began a project to update the floodplain maps for the Clark Fork and Bitterroot rivers in Missoula County. The floodplain maps are being updated so that these agencies will have the latest, most accurate flood risk information because the existing floodplain maps are based on data from the 1970s.
Why is floodplain mapping important to Missoulians?
New modeling technologies and current information allow us to understand the risk of flooding. This information is used to make planning decisions and require that structures be elevated so they are not damaged in a flood. Good data allows the City to protect residents' lives and investments in their property. Changes to the floodplain map could result in property owners being required to purchase flood insurance if their property is in an area remapped as being in a "Special Flood Hazard Area." For information on flood insurance and floodplain resources, visit the City Planning office's web page at https://www.ci.missoula.mt.us/2063/Floodplain-Administration.
Flood Study Steps
According to DNRC's website, the steps for updating the mapping are as follows:
Step 1 - Survey: Measurements are made of the topography around the river, along with any culverts, bridges, and road crossings. An airplane is used to collect ground elevation over a large area, and Ground Survey supplements the airborne data.
Step 2 - Hydrology: Determines how much water there will be in the river during a flood event. Data from stream gauges will tell how many cubic feet of water per second the river will carry during the flood.
Step 3 - Hydraulics: Once the first two steps are complete, calculations can show where the water will go during the flood. The elevation data is combined with the flood flow data to determine where the water will go when it overflows the channel.
Step 4 - Mapping (delineation): The results from step 3 are combined with the elevation data and official maps to see how far the water will spread out. The area shown to be underwater during the flood is the regulatory floodplain.
Detailed information is available on the DNRC's project page at http://dnrc.mt.gov/divisions/water/operations/floodplain-management/missoula-granite.
