Our river corridor rich with life, critical to the health of our river and fishery. Mapping and development standards help to encourage healthy development and limit damages to property and risk to safety as a result of flooding.

Big Hole River Approximate Zone A Floodplain Mapping

The Big Hole River Approximate Zone A (also referred to as the “100 year floodplain” or “1% flood probability”) were completed spring 2013. The mapping covered 116 miles of Big Hole River from headwaters to mouth, except the portion within Silver Bow County which had been mapped previously.


floodplain


Floodplain mapping provides legally defensible products for counties to regulate to within the floodplain. Appropriate river floodplain development is critical to ensure the health and safety of the public and responders during floods, the protection of property, and the long-term sustainability and health of our river floodplain, providing protections for water quality, river side vegetation, and more.


What is a “Floodplain” and why do we map it?


Adopting floodplain maps went through the following steps:

Step 1: Create accurate Floodplain Maps – COMPLETE


Step 2: State of Montana Adoption – COMPLETE 10/7/2014

See order online:
http://dnrc.mt.gov/divisions/water/operations/docs/floodplain/big-hole/Big_Hole_Study_Order_2015.pdf

See BHWC Announcement:
https://bhwc.org/2014/10/24/floodplain-maps/


– Intermediate Step: After state adoption, the state will submit the maps to FEMA for adoption. This process is expected to take several years to complete. The next steps are not dependent on this step.


Step 3: County Adoption & Floodplain Development Standards

Anaconda-Deer Lodge, Beaverhead and Madison County. (Butte-Silver Bow approved their floodplain maps in earlier mapping).

Each county may adopt floodplain development standards that will provide guidance on appropriate floodplain development, such as river set-backs, structure height, etc. The Big Hole Watershed Committee drafted recommended language for new development standards to encourage incorporation of riparian health standards as well as standardize floodplain development across counties. A letter of support was sent to counties April 2015 to encourage floodplain map and development standard adoption:

View the BHWC Letter of Support.

View BHWC Handout for County Adoption Process

The existing 150 foot setback floodplain standard is uniform among 4 counties, was developed by the BHWC Land Use Planning Committee, and remains in place.

  • Beaverhead County adopted maps and new development standards January 1, 2016.
  • Anaconda-Deer Lodge and Madison Counties are awaiting final map adoption.

View the Big Hole River Floodplain Maps

The Big Hole River Approximate Zone A Floodplain Maps up for state adoption may be viewed online:

View Big Hole River Floodplain Maps Online

The BHWC Land Use Planning Committee & The Floodplain Mapping Team

The BHWC Land Use Planning Committee has led the effort to map the Big Hole River floodplain beginning in 2009. The Land Use Planning Committee is a sub-committee of the BHWC. During this project, this sub-committee was led by facilitator Jen Boyer of Future West. The committee is made up of county planners, state floodplain advisors, landowners and interest groups.

The Big Hole River Floodplain Maps were developed through partnerships:


Resources:

Wikipedia’s description of the floodplain and why we map the floodplain.

The Nature Conservancy – “Why Rivers Flood and How to Reduce the Risk”

Montana DNRC Floodplain Management (Water Resources Division)

Annual Land Values Study, by Norman C Wheeler & Associates, Bozeman, MT