Dam Safety Program
Design & Construction
Water Storage Dams and Reservoirs
Dam safety statutes are enumerated in Idaho Code Title 42, Chapter 1709-1721. 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. The following illustration is offered for comparison with other commonly used definitions for dam height:
Dams greater than or equal to ten (10) feet height or reservoirs greater than or equal to fifty (50) acre-feet storage capacity are regulated by the Idaho Department of Water Resources Dam Safety Program (Department) unless specifically exempted per Idaho Code 42-1711. Prior to construction, an Application to Construct a Dam is required of any person who would build a dam that would meet these dimensions. Water storage projects must be approved by the Department prior to construction, and built according to the prescriptive design requirements listed in the Idaho Administrative Rules (IDAPA) 37.03.06; unless, alternately designed by an Idaho licensed professional engineer, and reviewed and approved by the Department, also prior to construction.
Owners who desire to construct, enlarge, alter or repair water storage or diversion dams greater than twenty (20) feet in height or reservoirs greater than or equal to one-hundred (100) acre-feet storage capacity shall submit an Application to Construct a Dam to the Department. The design plans and specifications for construction of any dam that would meet these dimensions shall be prepared by or under the direction of a licensed professional engineer who is registered pursuant to Idaho law, and shall be submitted for review and approval prior to beginning construction.
Whether or not the design is prescriptive or custom engineered by a currently licensed professional engineer in Idaho, inspection during construction shall be performed by the Department for the purpose of securing conformity with the approved plans and specifications. If at any time during construction, site inspection reveals the work is not being accomplished in accordance with the approval of the Department and the approved design, the Department 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 the Department in the same manner as water storage projects, with an additional provision that a surety bond be secured by the owner payable to the Department for reclamation of the project works. Design and construction requirements for Mine Tailings Impoundment Structures are described in IDAPA 37.03.05.
Inspections & Reports
The Department 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. However, all statutory sized dams must be inspected by the Department no less than every five (5) years. Persons interested in obtaining or reviewing copies of inspection reports prepared by the Department for non-federal dams may contact the State Office in Boise.
The Hazard rating that is used by the Department 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.
Other "Dam" Subjects: