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DNRC Headquarters
1539 Eleventh Ave. Helena, MT 59601
Phone: (406) 444-2074 | Fax: (406) 444-2684
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Floodplain Mapping FAQs

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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 an area that will be inundated by a 100-Year Flood, 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.

Floodplain Mapping Questions

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 the County 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.

Gallatin County has had Flood Insurance Rate Maps since 1978.  The County administers Floodplain Management Regulations in mapped 100-Year Floodplains to minimize flood losses and threats to public health, safety, and welfare.  Gallatin County's current Flood Insurance Rate Maps can be found on FEMA's Flood Map Service Center website: www.msc.fema.gov

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.
  • Gallatin County uses Flood Insurance Rate Maps:
    • To regulate flood risk areas.
    • To inform local emergency planning and mitigation, land-use planning, 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.  At this time, an updated flood study and floodplain mapping project for Bozeman Creek and its tributaries and the West Gallatin River is underway.

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. Any official Appeals or Comments submitted to FEMA during the 90-Day Appeal and Comment Period will need to reference a specific Preliminary Flood Insurance Rate Map panel number. The official FEMA Comment and Appeal Period is expected to occur in July-October 2018.

Project Questions

Why are the existing Flood Insurance Rate Maps being updated?

Most of the existing Flood Insurance Rate Maps for the West Gallatin River were delineated from a study completed in the late 1970s.  The existing Flood Insurance Rate Maps for Bozeman Creek, Matthew Bird Creek, Nash Spring Creek, Flat Creek, and Mill Ditch Diversion were delineated from studies conducted in the mid-1970s and mid-1980s.  New data and modern engineering methods are now being used to map the floodplains more accurately.  After a technical and public review process, the preliminary maps will eventually replace the existing Flood Insurance Rate Maps.

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.

Where can I see the proposed changes between existing Flood Insurance Rate Maps and the preliminary floodplain maps?

FEMA issued Preliminary Flood Insurance Rate Maps for this project in November 2016. The map viewers (links below) show the preliminary map data. You can also view the Preliminary Flood Insurance Rate Map panels here: Preliminary Flood Insurance Rate Maps.
Preliminary Floodplain Map Viewer—Basic
http://tiny.cc/SaferGallatin
Preliminary Floodplain Map Viewer—Advanced
http://gis.gallatin.mt.gov/floodplainmap/viewer/

Where can I find Preliminary Flood Insurance Rate Maps and Technical Reports?

Preliminary Flood Insurance Rate Maps, a Preliminary Flood Insurance Study, and Technical Hydrology and Hydraulic Reports are located at the link on the right side of the Gallatin Floodplain Mapping Update Project page. They can also be accessed here.

What is the project timeline?

Gallatin Timeline032318
At this stage of the project, Preliminary Flood Insurance Rate Maps are available.  The FEMA 90-Day public Appeal and Comment Period is projected to begin in July 2018.  Once public Appeals and Comments are resolved, new Flood Insurance Rate Maps from this project are expected to be finalized and become adopted in late 2019.

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 2019). 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?

Gallatin County’s floodplain regulations apply to areas located in the 100-Year Floodplain shown on Flood Insurance Rate Maps. The County requires a floodplain permit for any development projects in a mapped floodplain.

Preliminary Flood Insurance Rate Maps for the West Gallatin River and Bozeman Creek and its tributary streams are going through the review process and are not yet effective. Until these maps become effective, the County strongly encourages 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. Preliminary 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 County’s Floodplain Regulations with County staff to understand the impacts of Flood Insurance Rate Map updates on proposed construction projects in a mapped floodplain.