Idaho Administrative Code
Title IDAPA 37 - Water Resources, Department of
Rule 37.03.06 - SAFETY OF DAMS RULES
Section 37.03.06.010 - DEFINITIONS

01. Alterations or Repairs. Any activity that may affect the safety or integrity of a dam. Alterations and repairs do not include routine maintenance items.

02. Appurtenant Structures. Ancillary features (e.g., outlets, tunnels, gates, valves, spillways, auxiliary barriers, etc.) used for operation of a dam, which are owned or for which the owner has responsible control.

03. Artificial Barrier or Embankment. Any structure constructed to impede, obstruct, or store water.

04. Borrowed Fill Embankment. Any embankment constructed of borrowed earth materials, and which is designed for construction by conventional earth moving equipment.

05. Certificate of Approval. A certificate issued by the Director for all existing dams listing restrictions imposed by the Director, and without which none shall be allowed to impound water.

06. Conduit. A pipe or other constructed conveyance within a dam designed to release water or liquid in the reservoir.

07. Core. A zone of relatively low permeability material within an embankment.

08. Cutoff Trench. An excavation later to be filled with impermeable material during construction of a dam to limit seepage beneath the structure and through the foundation.

09. Dam. Any artificial barrier together with appurtenant works, which is or will be ten (10) feet or more in height and has or will have an impounding capacity at maximum storage elevation of fifty (50) acre-feet or more. Height of a dam is defined as the vertical distance from the natural bed of the stream or watercourse at the downstream toe of the barrier, as determined by the Director, or from the lowest elevation of the outside limit of the barrier, if it is not across a stream channel or watercourse, to the maximum water storage elevation. Under Section 42-1711, Idaho Code, the following are not included as regulated dams or are not considered dams for the purposes of Sections 42-1710 through 42-1721, Idaho Code:

10. Days. Calendar days including Sundays, Saturdays, and holidays.

11. Department. The Idaho Department of Water Resources.

12. Design Evaluation. The engineering analysis required to evaluate the performance of a dam relative to earthquakes, floods, or other site-specific conditions anticipated to affect the safety or operation of the dam, or appurtenant facilities.

13. Director. The Director of the Department of Water Resources.

14. Embankment. An artificial barrier constructed of earth, sand, rock, or gravel used to impound water.

15. Emergency Action Plan (EAP). A written plan with instructions to be taken to reduce the potential for property damage and loss of life in an area affected by a dam failure or uncontrolled release of stored contents.

16. Enlargement. Any change in or addition to an existing dam which raises or may raise the elevation of the contents impounded by the dam.

17. Factor of Safety. A ratio of available shear strength to shear stress, required for stability.

18. Flashboards. Structural members of timber, concrete, steel, or other erosion resistant material placed across a channel or entrance to a spillway to temporarily raise the surface level of the reservoir.

19. Flood. An increase in water surface elevation due to naturally occurring runoff or other rise in water levels that result in the inundation of areas not normally covered by water. As defined herein floods may be expressed in terms of average annual probability of exceedance, corresponding to values which may be described as flow rate, volume, or elevation (i.e., stage).

20. Flood Surcharge. A variable volume of water temporarily detained in a reservoir, in the space (or part thereof) that is filled by excess runoff or flood water, above the approved design maximum storage elevation. Flood surcharge is passed through the reservoir and discharged downstream until the reservoir level has been drawn down to the design maximum storage elevation.

21. Freeboard. Vertical height between the maximum design water surface elevation and the lowest elevation along the top of the dam. Freeboard can include a provision for variables such as wave height, flood surcharge, settlement, and flashboards.

22. Hazard Classification. The potential adverse incremental consequences to downstream life, property, and the environment resulting from the release of water or stored content due to dam failure or mis-operation of the dam, exclusive of the size or the physical condition of the dam. Hazard Classifications shall be assigned to new and existing dams based on potential adverse incremental impacts in three categories: downstream development, estimated loss of life, and economic losses.

23. Hydraulics. The study of the conveyance of liquid through pipes and channels.

24. Hydrology. The study of precipitation, snowmelt, and runoff in relation to land surfaces.

25. Inflow Design Flood (IDF). The flood specified for designing a dam, or appurtenant facility. Commonly expressed inflow design flood(s) include peak rate(s) of flow and volume(s) associated with floods having an annual exceedance probability of one percent (1%) (i.e., Q100) and zero point two percent (0.2%) (i.e., Q500), and the PMF (probable maximum flood).

26. Intermediate Dams. Artificial barriers twenty (20) feet or more in height but less than forty (40) feet or capable of storing one hundred (100) acre-feet of water or more but less than four thousand (4,000) acre-feet.

27. Large Dams. Artificial barriers forty (40) feet or more in height or capable of storing four thousand (4,000) acre-feet or more of water.

28. Levee. A retaining structure alongside a natural lake which has a length two hundred (200) times greater than its greatest height measured from the lowest elevation of the toe to the maximum crest elevation of the retaining structure.

29. Lift Construction. Embankment enlargement by raising the elevation of the structure on a continuous or recurring basis. Such practice will be considered under construction until the structure reaches its final crest elevation.

30. Maximum Water Storage Elevation. The maximum design elevation of the water surface or stored contents which can be impounded by the dam.

31. Operation Plan. A specific plan that promotes the safe operation of the dam for its intended purpose, and which provides specific limits and procedures for controlling inflow, storage, and/or release of water or slurry.

32. Owner. Includes any of the following who own, control, operate, maintain, manage, or propose to construct a dam, or reservoir:

33. Professional Engineer. A person licensed as a professional engineer by the Idaho Board of Licensure of Professional Engineers and Professional Land Surveyors under chapter 12, title 54, Idaho Code. For the purposes of this rule, the use of the term engineer implies a professional engineer consistent with this definition.

34. Release Capacity. The ability of a dam to pass excess water through the spillway(s) and outlet works, including the contribution from any designed conveyance through or around the dam.

35. Reservoir. Any basin which contains or will contain the water impounded by a dam.

36. Small Dams. Artificial barriers ten (10) feet or more in height but less than twenty (20) feet in height and that store fifty (50) acre-feet or more but less than one hundred (100) acre-feet of water.

37. Spillway. A constructed channel or other approved feature over, through, or around a dam, which is designed to accommodate the net inflow design flood and thus prevent overtopping by the reservoir.

38. Storage Capacity. The total storage in acre-feet at the maximum design storage elevation.