Although thousands of lives have been lost and substantial property damage has occurred as a result of dam failure, good planning and improved dam safety programs have reduced loss of life and property damages dramatically in recent years. Dam failures or partial failures are not usually caused by storm events. Most failures fall into one or more of the following categories:
Structural Failures - Foundation defects, including settlement and slope instability, or damage caused by earthquakes, have caused about 30 percent of all dam failures in the United States.
Mechanical Failures - Malfunctioning gates, conduits, or valves can cause dam failure or flooding both upstream and downstream and account for about 36 percent of all dam failures in the United States.
Hydraulic Failures - Overtopping of a dam is often a precursor to dam failure. National statistics show that overtopping due to inadequate spillway design, debris blockage of spillways, or settlement of the dam crest accounts for approximately 34 percent of all dam failures in the country.
In addition, these problems can lead to dam failure:
Inadequate design criteria
Malfunction of dam components
Spillway damage or malfunction
Embankment stability problems
Damage from vandalism
For more information, visit FEMA’s 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?
Dam owners can undertake several planning and preparedness activities that may help them better understand the risk related to their dam and improve emergency response actions. Activities such as conducting risk assessments, preparing emergency response plans, and identifying infrastructure in the flood zone through inundation mapping are beneficial for a dam owner.
Activities to Increase Dam Risk Awareness and Preparedness
Risk Assessment – The process of deciding whether existing risks are tolerable and present risk control measures are adequate and, if not, whether alternative risk control measures are justified. Risk assessment incorporates the risk analysis and risk evaluation phases. Use the Threat and Hazard Identification and Risk Assessment Guide to support risk assessment efforts.
Emergency Action Plan (EAP) – A plan of action to be taken to reduce the potential for property damage and loss of life in an area affected by a dam failure or large flood. See the Federal Guidelines for Dam Safety: Emergency Action Planning for Dam Owners for detailed guidance on emergency action planning and developing your EAP.
Inundation Map – A map showing areas that would be affected by flooding from releases from a dam’s reservoir. The flooding may be from either controlled or uncontrolled releases or because of a dam failure. A series of maps for a dam could show the incremental areas flooded by larger flood releases. See the Federal Guidelines for Inundation Mapping of Flood Risks Associated with Dam Incidents and Failures for detailed guidance on inundation mapping.
Check out ASDSO’s Responsible Dam Ownership – Information, Guidelines and Tools website for more detailed information and supporting materials.
Also, review the Flood Economics website, which provides insight into the economic benefits of flood mitigation.
In addition, the DHS Dams Sector Crisis Management Handbook provides information relating to emergency response and preparedness issues; includes recommendations for developing emergency action plans and site recovery plans.