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Types of Dams and Failure Modes

Identifying the type of dam you are responsible for and understanding potential failure modes for that type of dam is an important first step to improve dam safety. Equally important is knowing the warning signs for failure modes and how to effectively respond to them. Performing regular dam inspections is critical for early problem identification and intervention. All personnel responsible for the operation of the dam should be aware of the common failure modes and should be able to identify early warning signs for each failure mode.

Types of Dams

Here are examples of common types of dams (Source: USSD Types of Dams webpage)

Arch Dam - A concrete or masonry dam, which is curved upstream so as to transmit the major part of the water load to the abutments. A double curvature arch dam is an arch dam, which is curved vertically as well as horizontally.

Buttress Dam - A dam consisting of a watertight part supported at intervals on the downstream side by a series of buttresses. A buttress dam can take many forms, such as a flat slab or a massive head buttress. An Ambursen dam is a buttress dam in which the upstream part is a relatively thin flat slab usually made of reinforced concrete. A multiple arch dam is a buttress dam composed of a series of arches for the upstream face.

Coffer Dam - A temporary structure enclosing all or part of the construction area so that construction can proceed in a dry environment. A diversion cofferdam diverts a stream into a pipe, channel, tunnel, or other watercourse.

Diversion Dam - A dam built to divert water from a waterway or stream into a different watercourse.

Embankment Dam - Any dam constructed of excavated natural materials or of industrial waste materials. An earth dam is an embankment dam in which more than 50 percent of the total volume is formed of compacted earth material generally smaller than 3-inch size. A hydraulic fill dam is an embankment dam constructed of materials, often dredged, which are conveyed and placed by suspension in flowing water. A rockfill dam is an embankment dam in which more than 50 percent of the total volume is composed of compacted or dumped cobbles, boulders, rock fragments, or quarried rock generally larger than 3-inch size.

Gravity Dam - A dam constructed of concrete and/or masonry, which relies on its weight and internal strength for stability. A hollow gravity dam is a dam constructed of concrete and/or masonry on the outside but having a hollow interior relying on its weight for stability. A crib dam is a gravity dam built up of boxes, crossed timbers, or gabions filled with earth or rock. A roller-compacted concrete dam is a concrete gravity dam constructed by the use of a dry mix concrete transported by conventional construction equipment and compacted by rolling, usually with vibratory rollers.

Hydropower Dam - A dam that uses the difference in water level between the reservoir pool elevation and the tailwater elevation to turn a turbine to generate electricity.

Industrial Waste Dam - An embankment dam, usually built in stages, to create storage for the disposal of waste products from an industrial process. The waste products are conveyed as fine material suspended in water to the reservoir impounded by the embankment. The embankment may be built of conventional materials but sometimes incorporates suitable waste products. A mine tailings dam is an industrial waste dam in which the waste materials come from mining operations or mineral processing.

Masonry Dam - Any dam constructed mainly of stone, brick, or concrete blocks jointed with mortar. A dam having only a masonry facing should not be referred to as a masonry dam. A rubble dam is a stone masonry dam in which the stones are unshaped or uncoursed.

Overflow Dam - A dam designed to be overtopped.

Regulating (Afterbay) Dam - A dam impounding a reservoir from which water is released to regulate the flow downstream.

Saddle Dam (or Dike) - A subsidiary dam of any type constructed across a saddle or low point on the perimeter of a reservoir.

Resources

Several resources are available to help dam owners identify the type of dam they are responsible for, and learn about failure modes and conditions to watch for during inspection that could indicate a potential safety issue; and most importantly, learn how to effectively respond to issues.

  • FEMA’s Pocket Safety Guide for Dams, Impoundments - This guide was developed as a quick reference to help dam owners and others assess low hazard dams and impoundsments. Uncontrolled release of a reservoir resulting from a dam failure can have a devastating effect on people property downstream. Safely maintaining a dam is a key elemet in preventing dam failure and limiting the liability a dam owner could face.

  • ASDSO’s Introduction to Dams webpage - This webpage provides an overview of how dams are built and how they work, as well as causes of dam failure.

  • Living with Dams: Know Your Risk - This booklet is designed to help answer questions about dams: what purposes they serve, associated risks, guidance for those living near dams, and where to find further information. The booklet provides a general overview of dams and dam safety, and answers the following questions: Why should I care about dams? What are the risks associated with dams? Could I be affected by a dam? What is the dam failure flood inundation area? Once I determine that my property is in a dambreak inundation area, what's next?

  • PBS’s Dam Basics webpage - A beginner-friendly resource outlining dam types and the forces that affect each

  • Montana Dept. of Natural Resources and Conservation’s Dam Owner Emergency Intervention Toolbox - The Dam Emergency Intervention Toolbox was developed to provide owners of dams throughout the U.S. with the necessary information and tools to identify and remedy unsafe conditions which may develop. In addition to presenting identification techniques and intervention actions that may be performed to prevent or delay an incident resulting from an observed unusual dam condition, the toolbox includes background information on embankment dams, inspection guidelines, and recordation practices for monitoring procedures.

  • Bureau of Reclamation’s Overview of Failure Modes - This graphic-heavy presentation highlights types of dams and their features, and provides an overview of potential failure modes for each.

Last Updated: 
10/02/2019 - 11:14