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

ARM 36.14.201 states: "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.
  • If DNRC has previously conducted a hazard classification analysis on the dam, a waiver to the application requirement can be requested.  In order to be eligible for a waiver, the dam and reservoir must be the same size as the previous classification and there must be no additional development downstream. Requests for a waiver can be made to your local Regional Engineer
  • 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.

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.

Special Note: There are many reasons why dam owners often prefer to have their engineer complete the analysis:

  • DNRC engineers make many conservative and simplifying assumptions, as they are given a short time frame in the law to make a determination. It is in a dam owners best interest to have an accurate understanding of what happens in a dam failure. To accurately make this determination, a robust analysis may be warranted.
  • If there are clear hazards downstream, and a high-hazard classification is likely, the owner will need to develop an inundation/evacuation map for an Emergency Action Plan anyway.  There may also be a need to develop a detailed inundation map to evaluate spillway adequacy.  The analysis completed by DNRC engineers is not suitable for the Emergency Action Plan nor for a spillway analysis.

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.


  • 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.
  • 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. Recent Red Tape Reduction Rule Changes gave DNRC the authority to waive the hazard classification requirement if it is clear the impact downstream is unchanged.

A hazard classification is not required for dams that store under 50 acre-feet measured to normal operating level.  However, being under 50 acre feet does not relieve a dam owner of responsibility.

Please go to Resources for Small Dams (Under 50 Acre Feet in Capacity) for more information.

Rules & Laws Pertaining to Hazard Classifications

Montana Code Annotated (Law)

Administrative Rules of Montana (Rules)


Maximum Normal Operating Pool - ARM 36.14.101(12)

(a) means the elevation of lowest uncontrolled principal spillway for on-stream reservoirs;
(b) means the elevation of the emergency spillway for flood control structures; and
(c) is defined on a case-by-case basis according to reservoir operation for off-stream