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DNRC Headquarters
1539 Eleventh Ave. Helena, MT 59601
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Hazard Classifications

LWC downstream.JPG

To build a new dam or alter an existing dam with an impoundment capacity of 50 acre feet or more, you must apply to the DNRC Dam Safety Program for a Hazard Classification.

So What is a Hazard Classification?

A Hazard Classification  involves an evaluation of the area downstream from the dam that would be flooded if the dam fails under clear weather conditions. If the flooding caused by the dam failure is likely to cause a loss of life, the dam or reservoir is classified as a High-Hazard structure. The purpose of a Hazard Classification is to determine if additional dam safety permits are required.

  • Dams classified as High Hazard are required to obtain additional construction and operating permits as described in Permitting your Existing Dam or Proposing to Build a New Dam.
  • Dams classified as Not High Hazard are not required to obtain additional construction and operation permits from the Dam Safety Program.


IMPORTANT NOTE: A Hazard Classification is NOT:

  • An assessment of the safety of the structure.
  • A statement as to what will happen downstream should a dam fail
  • A assessment of what could happen during a flood.  There could be risk to life at reservoir levels above what is used in the Classification.


Special Note:  State law requires all dams, including those classified as NOT high hazard, to be maintained and operated in a safe and secure manner.  DNRC has both the authority and the obligation to take action if necessary to assure protection of life and property downstream of ANY dam.


 Who has to Apply for a Hazard Classification? (ARM 36.14.201)

Any person, agency or organization proposing to construct, alter, repair, enlarge, or remove any dam or reservoir that has or could impound to the maximum normal operating pool 50 acre-feet or more must apply for a Hazard Classification.

Special Notes

  • The Hazard Classification must be issued BEFORE the work is initiated
  • Dams already classified as high-hazard are not required to reapply for a hazard determination
  • Dams exempt from the Montana Dam Safety Act do not need to apply:
    • Hydropower Dams (dams regulated by the Federal Emergency Regulatory Agency (FERC)
    • Tailings Dams on active mines (dams permitted by the DEQ Hard Rock Mining Bureau)
    • Federally owned dams (dams permitted by federal agencies such as the US Bureau of Reclamation, Army Corp of Engineer, US Fish and Wildlife Service, US Forest Service, US Bureau of Land Management)
    • Private dams on federal property when the federal agency owning the property has regulatory oversight.
  • Dams where loss of life from dam failure is not likely to occur do not need to apply:
    • Diversion dams
    • Levees on the bank of a natural lake or stream
    • Railroad and highway embankments not intended to store water
    • Naturally occurring reservoirs
    • Wastewater pond dams that are subject to the regulation under the Dept. Environmental Quality


How does a Dam Owner Apply for a Hazard Classification?

There are two approaches that can be used:

  1. The dam owner hires a qualified engineering consultant to conduct the analysis following methods described in DNRC Technical Note 6 and provides to the appropriate DNRC Regional Engineer along with the Application for Determination of Hazard Classification of Dams and Reservoirs ($125 Fee).  DNRC will review the consultants work and assign a Hazard Classification.

  2. The dam owner submits the Application for Determination of Hazard Classification of Dams and Reservoirs with their estimates of reservoir storage and dam heights along with the required $125 fee to the appropriate DNRC Regional Engineer.  DNRC will conduct a simple analysis of the downstream hazard according to Technical Note 6 and assign a Hazard Classification.


Is a Hazard Classification Necessary if a Dam Has Been Previously Classified?

If a repair (or removal) of a dam is planned, generally, a new Hazard Classification Application is required, even if the dam was classified previously (ARM 36.14.201 (1)).


  1. if the dam is already classified as High Hazard, and there is no reason to believe this is changed, a new Classification is not required. (ARM 36.14.201 (1) (a))
  2. If capacity and height of the dam is not being increased, there is no additional downstream development, and the original analysis is available for review, please contact your local dam safety Regional Engineer to discuss. DNRC can discuss a modified hazard classification requirement if it is clear the impact downstream is unchanged.


What if My Dam Stores Under 50 Acre Feet?