Dam Failure

A dam is a barrier across flowing water that obstructs, directs, or slows down water flow. Dams provide benefits such as flood protection, power generation, drinking water, irrigation, and recreation. Failure of these structures results in an uncontrolled release of impounded water. Failures are relatively rare, but immense damage and loss of life is possible in downstream communities when such events occur. Aging infrastructure, hydrologic, hydraulic and geologic characteristics, population growth, and design and maintenance practices should be considered when assessing dam failure hazards. Dam failure most often occurs during or after a massive rainfall, flooding, or spring thaws, sometimes with little to no warning. Catastrophic failures are characterized by the sudden, rapid, and uncontrolled release of impounded water or any other fluid or semi-fluid from a dammed impoundment or water body. Pennsylvania uses three categories to classify dam hazards: High, Significant, and Low (FEMA, April 2004). Dam failures may or may not leave enough time for evacuation of people and property, depending on their abruptness.

In recent years, the failure of navigation locks has become an increasing concern for Western Pennsylvania. A lock is a device used for raising and lowering boats between stretches of waterways with different water levels. In Pennsylvania, locks are primarily located on the Allegheny, Monongahela, and Ohio Rivers.

Provided that adequate engineering and maintenance measures are in place, high hazard dam failures and lock failures are unlikely in Pennsylvania. Dam Emergency Action Plans drafted in accordance with the Federal Guidelines for Dam Safety identify the risk related information include the inundation area and the time lapse between failure and flooding reaching specific destinations downstream. Approximately 902 of the 3,429 dams located in Pennsylvania are regulated by DEP have approved Emergency Action Plans. These plans are also reviewed and approved by PEMA.

Click on an icon below for a summary of each hazard.

Hazard: Human-made
HIRA Ranking: 2.4
THIRA Ranking: 3.1

Vulnerable State Facilities: Protected
Vulnerable Critical Facilities: Protected
Vulnerable Population: Protected
Exposed Building Value: Protected

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