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DNRC Headquarters
1539 Eleventh Ave. Helena, MT 59601
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Frequently Asked Questions

General Questions

What are floodplains?

Floodplains are areas along a waterway that are prone to flooding. Flooding can happen anywhere, but certain areas are especially prone to flooding from waterways.


What is a 100-year floodplain (1% Annual Chance Floodplain)?

A 100-Year Floodplain (1% Annual Chance Floodplain) is a flood event having a 1% chance of being equaled or exceeded in any given year. In a 100-Year Floodplain, there is at least a 1-in-4 chance of flooding during a 30-year mortgage. The 100-Year Flood is also referred to as 1% Annual Chance Flood or a Base Flood.

The 100-Year Floodplain is the area designated by the Federal Emergency Management Agency (FEMA) and the State of Montana as a high-risk area for floodplain management and flood insurance purposes.


What is the difference between the 100-year (1% Annual Chance) floodplain and the Floodway?

A 100-Year Floodplain (1% Annual Chance Floodplain) is considered to have a HIGH flood risk. It is the area that is expected to be inundated by a 100-Year Flood, an event having a 1% chance of being equaled or exceeded in any given year. The 100-Year Flood is also referred to as a 1% Annual Chance Flood or a Base Flood. 

 A FLOODWAY is the area within a 100-Year Floodplain that must be kept free from new development so that the 100-Year Flood (1% Annual Chance Flood, Base Flood) can be carried without substantial increases in flood heights. The Floodway will usually see the highest water velocities and deepest inundation during a 100-Year Flood event.


What are the different flood risk areas or flood zones?

There are many different terms used to describe flood risk. Everyone lives in an area with some flood risk—it’s just a question of whether you live in a high-risk, low-risk, or moderate-risk flood area.

Flood zones are indicated on a community’s flood map. Each flood zone describes the flood risk for a particular area, and those flood zones are used to determine insurance requirements and costs.

Flood Risk Categories

Terms used to identify risk

Zones found on a FIRM

High Risk


100-year floodplain

1% Annual Chance

Zone AE with Floodway

Zone AE

Zone A

Moderate Risk

500-year floodplain

.2% Annual Chance

Shaded zone x

Low Risk


Unshaded zone x

Undetermined Risk

Undetermined risk

Zone D

Floodplain Mapping Questions

Is climate change considered with new flood studies?

The mapping follows FEMA/State standards which does not evaluate Future Conditions such as climate change.  To evaluate climate change, scientific trends analyses are necessary, which have yet to be completed for Montana. 


 Why are floodplains mapped?

Floodplains are mapped to accurately depict flood risk and understanding flood risk is the first step towards flood protection. Accurate floodplain maps help residents, businesses, and local officials make informed decisions to ensure personal safety, protect financial assets, and plan for emergencies.


What is a Flood Insurance Rate Map?

The Federal Emergency Management Agency (FEMA) works with the State of Montana and its communities to conduct flood studies and depict flood hazards on FEMA flood maps, known as Flood Insurance Rate Maps.  Flood Insurance Rate Maps illustrate the extent of flood hazards in a community by depicting a variety of information.

Counties, Cities, and Towns administer Floodplain Management Regulations in mapped 100-Year Floodplains to minimize flood losses and threats to public health, safety, and welfare.  Current Flood Insurance Rate Maps can be found on FEMA's Flood Map Service Center website:


How are Flood Insurance Rate Maps used?

Flood Insurance Rate Maps indicate areas of flood risk and they are used by different entities for a variety of reasons.

  • To regulate flood risk areas.
  • To inform local emergency planning and mitigation, land-use planning, sanitation, and growth policies.
    • Property owners and developers use Flood Insurance Rate Maps for subdivision and planning purposes.
    • Lenders use Flood Insurance Rate Maps to determine if a structure is in an area of flood risk.
    • Insurance Agents use Flood Insurance Rate Maps to determine flood insurance policies and premiums.

Flood Insurance Rate Maps need periodic updating if an area has changed or if better information becomes available.


Is there a difference between a "draft floodplain map" and a "Preliminary Flood Insurance Rate Map"?

Generally, there are minor differences between draft floodplain maps and Preliminary Flood Insurance Rate Maps. FEMA uses the draft floodplain map data to create Preliminary Flood Insurance Rate Maps. Therefore, Preliminary Flood Insurance Rate Maps are very similar to draft floodplain maps but with minor updates. In addition, unlike draft floodplain maps, Preliminary Flood Insurance Rate Maps have been fully converted to FEMA’s Flood Insurance Rate Map format. 


Project Questions

Why are the existing Flood Insurance Rate Maps being updated?
New data and modern engineering methods are now being used to map the floodplains more accurately. Most of the floodplain maps in the study area do not accurately reflect the flooding risk. DNRC works with communities across the state to update floodplain maps to ensure the flood risk in their community is accurate. This helps communities prepare for future flooding events and to work towards ways to reduce the impact of flooding.


What measures are in place to ensure the information used for the update will be as accurate as possible?
High-accuracy topographic information, updated hydrologic data, and more modern engineering methods are being used to ensure the maps reflect the flood risk accurately.


What if I disagree with the draft maps or I have new data?

FEMA will hold a formal 90-day appeal period tentatively late 2021. FEMA’s process follows certain guidance on what information could be submitted. For more information you can visit the project website.

DNRC encourages an early review and feedback of the draft data.



Where can I see the proposed changes between existing Flood Insurance Rate Maps and the draft maps?
 visit the project website at or contact your local Floodplain administrator.


If we don’t like the study results can we not use the new maps and continue to use the old maps?

New studies and maps provide an opportunity to assess current community risks. This information is critical to reduce flood damages and losses in a community. This information needs to be reviewed and reevaluated periodically. It is the community’s responsibility to review this information and provide formal updates in order to adequately reflect the current flood risk. At the end of the day it comes down to protecting property owners and the community.


Insurance Questions

Will I be required to purchase flood insurance based on the proposed changes shown in the Preliminary Flood Insurance Rate Maps?

It depends. Lenders can require flood insurance for a building they are financing, regardless of where the building is located. For federally backed loans, a lender must require flood insurance when a building is in a mapped 100-Year Floodplain, unless it can be proven that the building is actually above the flood elevation or outside of the floodplain. Periodically, lenders will review their loans to reassess flood risk based on the best available data. Flood Insurance Rate Map updates will typically trigger a periodic review.

Some property owners may not see any insurance changes with this mapping update. For areas that will be newly mapped into the floodplain, a lender may require flood insurance and/or elevation documentation for a building. If you own a building in an area that will be newly mapped into a 100-Year Floodplain, contact your lender as early as possible to start the discussion about flood insurance.


Can I get a subsidy on my flood insurance premiums if my property is newly mapped into a 100-Year Floodplain?

Yes. Buildings in newly mapped areas are eligible for subsidized premiums as long as flood insurance is purchased within 11 months of the date the new Flood Insurance Rate Maps become effective (estimated for late 2021). If you own a building in an area that will be newly mapped into a 100-Year Floodplain, contact your lender as early as possible to start the discussion about flood insurance.


Am I required to purchase flood insurance even though my building is not (and will not be) shown in a 100-Year Floodplain?

It depends. A lender does not need to require flood insurance when a building carrying a federally backed loan is located outside of a 100-year floodplain due to a decreased flood risk. A lender may still require flood insurance regardless of a building’s location, however, in order to protect their investment.

Every building has a risk of flooding even if it is not located in a high-risk, 100-Year Floodplain. It is therefore recommended that you purchase flood insurance even if your lender does not require you to do so.


Development Questions

I want to develop my property. How could the proposed floodplain changes affect me?

Floodplain regulations apply to areas located in the 100-Year Floodplain shown on floodplain maps. The County’s, Cities, and Town’s require a floodplain permit for any development projects in a mapped floodplain.

Draft maps are going through the review process and are not yet effective. Until these maps become effective, the communities strongly encourage proposed construction projects on properties newly mapped into a higher-risk flood zone to utilize draft map data to ensure that property development methods will minimize flood damage. Draft map data also provides an opportunity to develop smarter and thereby reduce potentially high costs of flood insurance premiums.

It is important to discuss the Floodplain Regulations with county, city, or town staff to understand the impacts of Flood Insurance Rate Map updates on proposed construction projects in a mapped floodplain.


What is the difference for development in the floodway vs the 100-year floodplain?

One area of the 100-year floodplain that is different, is the floodway portion.  This is the area where we typically see the deepest and fastest moving water during that 100-year flood event because of that there is no new buildings allowed in a floodway and very little development is allowed.

Development in the 100- year floodplain is allowed but requires a floodplain permit prior to any construction.


Does my community have floodplain regulations?

These are the communities within the project area that regulate development within the 100-year floodplain and the community points of contact.


Gallatin County

Sean O’Callaghan


Madison County

Alex Hogle



Jefferson County

Megan Bullock


Broadwater County

Jerry Grebenc


City of Three Forks

Kelly Smith


Town of Ennis

Jonathan Weaver


Town of Twin Bridges

Jonathan Weaver


Town of Sheridan

Bob Stump



To find out more on your community’s floodplain regulations please contact your local floodplain administrator.

More Info

Floodplain FAQs

Maps and Technical Reports

Flood Study Process


Madison County

Cody Marxer
Floodplain Administrator
(406) 872-6359

Town of Ennis
Town of Twin Bridges

Jonathan Weaver
Floodplain Administrator
(406) 449-8627

Town of Sheridan

Bob Stump
Mayor/Floodplain Administrator
(406) 842-5431

Gallatin County

Sean O'Callaghan
Floodplain Administrator
(406) 582-3130

City of Three Forks

Kelly Smith
Floodplain Administrator
(406) 285-3431

Jefferson County

Megan Bullock
Floodplain Administrator
(406) 225-4126

Broadwater County

Jerry Grebenc
Floodplain Administrator
(406) 449-8627

DNRC Contacts

Nadene Wadsworth
DNRC Outreach Specialist
(406) 444-6732

Tiffany Lyden
DNRC Outreach Specialist
(406) 444-0599