2 CCR 402-1-4 - Definitions

4.1 Alteration, Modification, Repair, or Enlargement of an Existing Dam and/or Appurtenant Structures. Construction that could affect the safety of the dam.

4.2 Annual Exceedance Probability (AEP). The probability of occurrence in any one year.

4.3 Appurtenant Structure. Component other than the material structure of the dam itself such as the outlet works and controls, spillways and controls, access structures, bridges, and other systems directly related to the safe operation of a dam.

4.4 Breach Order. An order issued by the State Engineer, or the State Engineer's designee, for removal of all or part of a dam to permanently reduce the maximum storage level, minimize the risk of failure, and/or the potential of damage downstream due to the failure of the dam.

4.5 Capacity. As used in section 37-87-105(1), C.R.S., the volume of water impounded by a dam at the high water line. Storage below the natural surface of the ground and low-level outlet is generally excluded.

4.6 Dam. A constructed barrier, together with appurtenant structures, constructed above ground surface for the purpose of impounding water. Flood control and storm runoff detention dams are included.

4.6.1 Jurisdictional Size Dam. A dam creating a reservoir with a capacity of more than one hundred (100) acre-feet, or a surface area in excess of twenty (20) acres at the high water line, or where the jurisdictional height exceeds ten (10) feet. Jurisdictional height is defined in Rule 4.7.1.

4.6.2 Non-Jurisdictional Size Dam. A dam creating a reservoir with a capacity of one hundred (100) acre-feet or less, and a surface area of twenty (20) acres or less, and a jurisdictional height of ten (10) feet or less. Non-jurisdictional size dams are regulated and subject to the authority of the State Engineer.

4.6.3 Diversion Dam. A dam constructed for the primary purpose of diverting water from a natural watercourse into a canal, tunnel, ditch, or pipeline.

4.6.4 Flood Control Dam. A dam that is normally dry and has an ungated outlet structure for the controlled release of water impounded during and subsequent to a flood event.

4.7 Dam Height. (See Figure 4.1)

4.7.1 Jurisdictional Height. The vertical dimension measured from the lowest point of the natural surface of the ground or the invert of the outlet pipe, whichever is lower, where the low point occurs along the longitudinal centerline of the dam crest, to the emergency spillway crest.

4.7.2 Hydraulic Height. The vertical dimension measured from the lowest point of the upstream toe of the dam to the emergency spillway crest.

4.7.3 Structural Height. The vertical dimension measured from the lowest point of the excavated foundation to the crest of the dam.

Figure 4.1: Determination of Dam Heights

Click to view image

4.8 Inundation Map. A map depicting the area downstream from a dam that would reasonably be expected to be flooded in the event of a dam failure.

4.9 Emergency Action Plan (EAP). A living document containing a written plan of actions used by an emergency response team to minimize property damage and loss of life in an area affected by a dam failure or large flood.

4.10 Engineer. An Engineer registered and licensed in Colorado in accordance with article 12-120, Part 2, C.R.S. The Engineer will be in "responsible charge," as defined in section 12-120-202, C.R.S., of the design and of the observation of construction. In general, the Engineer is responsible for the following:

A. Demonstrating a minimum of five years of experience as a registered Engineer in the design, construction, and safety evaluation of the type of dam under review;

B. Understanding all applicable regulatory requirements of the project and the required work, analyses, and oversight needed to complete a safe design and to observe construction to evaluate compliance with plans and specifications of the project;

C. Using current state of the practice methods and means to site and design dams with safety as the primary goal and to complete engineering methodology that represents the professional level of care exercised by qualified engineers; and

D. If necessary, assembling and supervising a team of qualified engineers, geologists, geological engineers, and other professionals as required to address all of the disciplines for the design and the observation of construction of a dam.

4.11 Freeboard.

4.11.1 Normal Freeboard. The vertical dimension between a spillway crest and the lowest point on the dam crest.

4.11.2 Residual Freeboard. The vertical dimension between the maximum water surface elevation during a flood event and the lowest point on the dam crest.

4.12 Geologist. An individual possessing specific knowledge of the geological sciences and the principles of engineering analysis and design acquired by professional education or demonstrated experience related to dams, and qualified to apply such knowledge to ensure geologic elements affecting the dam are adequately accounted for in design and construction.

4.13 Hazard Classification. One of four categories defined below as determined by analysis of potential consequences from a sunny day failure of the dam. Conditions for evaluation are absent flooding and the reservoir is assumed to be full to the high water line at the time of failure. The hazard classification establishes all the design criteria for a dam except for spillway size, which is controlled by the Hydrologic Hazard defined in Rule 4.15.

4.13.1 High Hazard. A dam for which life loss is expected to result from failure of the dam.

4.13.2 Significant Hazard. A dam for which significant damage, but no life loss is expected to result from failure of the dam. Significant damage is defined as damage to structures where people generally live, work, or recreate, including public and private facilities. Significant damage is determined to be damage sufficient to render structures or facilities uninhabitable or inoperable.

4.13.3 Low Hazard. A dam for which neither life loss nor significant damage as defined for a Significant Hazard dam are expected to result from failure of the dam.

4.13.4 No Public Hazard (NPH). A dam for which minimal damage, with no life loss, is expected to result from failure of the dam.

4.14 High Water Line. The elevation of the emergency spillway crest. If no emergency spillway exists, the elevation of the dam crest.

4.15 Hydrologic Hazard. Potential consequences downstream of a dam caused by floodwaters released by overtopping failure of the dam. Hydrologic hazard establishes design criteria for spillway size.

4.15.1 Extreme. Life loss potential of 1 or more.

4.15.2 High. Life loss potential of less than 1.

4.15.3 Significant. No life loss potential but significant damage is expected to occur.

4.15.4 Low. No life loss potential or significant damage is expected to occur.

4.16 Incremental Consequences. The difference in impacts that would occur due to failure or misoperation of the dam over those that would have occurred without failure or misoperation of the dam or appurtenances.

4.17 Inflow Design Flood (IDF). The flood hydrograph used to determine if the emergency spillway's hydraulic capacity meets the safety standards as defined in Rule 7.2.

4.18 Natural Surface of the Ground. The undisturbed ground surface before excavation, or the undisturbed bed of a natural watercourse.

4.19 Normal Water Line. The elevation of the service spillway crest. If there is no service spillway, the normal water line and high water line are the same.

4.20 Outlet. A conduit (usually regulated by gates or valves) used for releasing impounded water from the reservoir.

4.21 Owner. The person or persons in control of the physical structure of any dam in accordance with section 37-87-104.5, C.R.S. Person or persons refers to any individual, private or non-profit company, special district, federal, state, or local government agency, or any other entity in direct routine control of a dam and reservoir, and/or directly involved in the physical operation and maintenance of a dam, and/or proposes to construct a dam.

4.22 Plans. All necessary drawings, cross-sections, tables, notes, maps and other information necessary to accompany the construction specifications for design review and approval, and construction of a dam.

4.23 Potential Failure Mode (PFM). A physically plausible process for dam failure resulting from an existing inadequacy or defect related to a natural foundation condition, the design or construction of the dam or appurtenant structures, the materials incorporated, the operations and maintenance, or the aging process, which can lead to an uncontrolled release of the reservoir.

4.24 Potential Failure Modes Analysis (PFMA). The process by which the site-specific PFMs are identified, described in detail, and evaluated to determine the likelihood and confidence of occurrence.

4.25 Probable Maximum Flood (PMF). The flood that may be expected from the most severe combination of critical meteorologic and hydrologic conditions that are reasonably possible in the drainage basin under study.

4.26 Probable Maximum Precipitation (PMP). The theoretically greatest depth of precipitation for a given duration that is physically possible over a drainage basin.

4.27 Reservoir. A body of water impounded by a dam.

4.28 Restriction Order. An order issued by the State Engineer to limit the water surface elevation of a reservoir to no greater than the safe storage level.

4.29 Risk. The product of (1) the likelihood of a structure being loaded, (2) the likelihood of adverse structural performance, and (3) the magnitude of the resulting consequences.

4.29.1 Risk Management. Action implemented to communicate the risks and either accept, avoid, transfer, or control the risks to an acceptable level considering associated costs and benefits of any action taken.

4.29.2 Risk Analysis. Qualitative or quantitative procedures that consider likelihood of failure and magnitude of resulting consequences to evaluate the significance of PFMs.

4.30 Safe Storage Level. The maximum reservoir water surface elevation at which the State Engineer has determined that the dam is safe to impound water based on the safety inspection and/or evaluations.

4.31 Safety Inspection. An evaluation by an Engineer in accordance with section 37-87-107, C.R.S., used by the State Engineer to set the safe storage level. The inspection shall include a review of the Emergency Action Plan and the hazard classification of the dam.

4.32 Spillway. An overflow structure through which inflow is discharged from a reservoir.

4.32.1 Service Spillway. The overflow structure designed to limit or control the operating level of a reservoir.

4.32.2 Emergency Spillway. The overflow structure designed to pass the Inflow Design Flood.

4.32.3 Spillway Crest. The elevation of the spillway at which uncontrolled discharge begins.

4.33 Storage.

4.33.1 Normal Storage. Volume of the reservoir impounded by a dam below the normal water line.

4.33.2 Maximum Storage. Volume of the reservoir impounded by a dam below the dam crest.

4.33.3 Flood Storage. Volume of water temporarily stored within a reservoir between the normal water line and the crest of the dam.

Notes

2 CCR 402-1-4

42 CR 23, December 10, 2019, effective 1/1/2020