Dam Safety Program

Dam Saftey Program Overview

IDWR currently regulates nearly 600 water storage dams and more than 20 mine tailings impoundment structures located throughout the state. Dam Safety program personnel perform regular inspections of existing projects according to the potential consequences that a dam failure and sudden release of water would present to downstream life and property. The frequency between individual dam inspections depends on such items as the project’s physical condition, method of construction, maintenance record, age, hazard rating, and size and storage capacity. All statutory sized dams must be inspected by IDWR no less than every five (5) years.

Water Storage Dams & Reservoirs

Dam safety statutes are enumerated in Idaho Code §§ 42-1709 through 42-1721.

Hydraulic structures greater than or equal to ten (10) feet height and reservoirs that impound a volume of water greater than or equal to fifty (50) acre-feet are regulated by the IDWR Dam Safety Program for benefit of public safety, unless specifically exempted per Idaho Code § 42-1711.

The definition of height to be used for determining compliance with Idaho Code is measured vertically from the natural bed of the stream or watercourse at the downstream toe of the barrier to the maximum water storage elevation. However, regardless of size, any water storage embankment may be regulated for public safety if IDWR determines that the potential failure consequences would result in significant damage to downstream life or property.

Owners who desire to construct, enlarge, alter, or repair a water storage dam or water diversion structure meeting the definition and dimensions described above must submit an Application for Construction or Enlargement of a New or Existing Dam. In addition to submitting an application with the requisite fees, the owner must also submit a properly prepared design for IDWR’s review and approval. The design will be expected to meet or exceed the prescriptive design and construction requirements enumerated in the IDAPA 37.03.06.

Persons who propose to construct a dam or hydraulic structure equal to or greater than ten (10) feet high and with a corresponding reservoir volume greater than or equal to fifty (50) acre-feet capacity must engage the services of a qualified professional engineer who is currently licensed in Idaho. The design drawings, reports, specifications, and other design information deemed necessary for construction shall bear the engineer’s professional seal and signature, and shall be submitted to IDWR for review and approval. Inspection during construction shall be performed by IDWR for the purpose of securing conformity with the approved plans and specifications. If, at any time during construction, site inspection reveals that the work is not being accomplished in accordance with the approval of IDWR and the approved design, IDWR may order that no further work be done until compliance has been effected and approved.

Mine Tailings Impoundment Structures

Mine Tailings Impoundment structures greater than or equal to thirty (30) feet height are regulated by IDWR in the same manner as water storage projects, with an additional provision that a surety bond be secured by the owner payable to IDWR for reclamation of the project works.

Design and construction requirements for Mine Tailings Impoundment Structures are described in IDAPA 37.03.05.

The Hazard rating that is used by IDWR to classify dams and reservoirs is based on a three-tier system consisting of Low, Significant and High-hazard categories. It is important to note that the hazard classification assigned to any particular structure is based solely on the potential consequences to downstream life and property that would result from a failure of the dam and sudden release of water. Hazard is not to be used synonymously with the term “Risk” as they are not the same meaning. Risk incorporates a probability of failure; thus risk is equal to the probability of occurrence multiplied by the consequences that would result from a dam failure.

High Hazard – A high-hazard rating does not imply or otherwise suggest that a dam suffers from an increased risk for failure. It simply means that if failure were to occur, the resulting consequences likely would be a direct loss of human life and extensive property damage. For this reason all high-hazard dams must be properly designed, and at all times responsibly maintained and safely operated because the consequences of failure are so great. IDWR considers the inundation of residential structures with flood water from a dam break to a depth greater than or equal to two (2) feet to be a sufficient reason for assigning to a dam a high-hazard rating. An up-to-date Emergency Action Plan is a requirement for all owners of High hazard dams.
Significant Hazard – Significant hazard dams are those structures whose failure would result in significant damage to developed downstream property and infrastructure or that may result in an indirect loss of human life. An example of the latter would be a scenario where a roadway is washed out and people are killed or injured in an automobile crash caused by the damaged pavement.
Low Hazard – Low hazard dams typically are located in sparsely populated areas that would be largely unaffected by a breach of the dam. Although the dam and appurtenant works may be totally destroyed, damages to downstream property would be restricted to undeveloped land with minimal impacts to existing infrastructure.

View the status and downstream hazard potential for dams in Idaho.
Need a larger map? Click here to view a full-size interactive map of the dams in Idaho.

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