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National Inventory of Dams

The National Inventory of Dams (NID) is now available.

National Inventory of Dams

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National Inventory of Dams History

Congress first authorized the U.S. Army Corps of Engineers (USACE) to inventory dams in the United States with the National Dam Inspection Act (Public Law 92-367) of 1972. The NID was first published in 1975, with a few updates as resources permitted over the next ten years.

The Water Resources Development Act of 1986 (P.L. 99-662) authorized USACE to maintain and periodically publish an updated NID, with re-authorization and a dedicated funding source provided under the Water Resources Development Act of 1996 (P.L. 104-3). USACE also began close collaboration with the Federal Emergency Management Agency (FEMA) and state regulatory offices to obtain more accurate and complete information.

The National Dam Safety and Security Act of 2002 (P.L. 107-310) and the Dam Safety Act of 2006 reauthorized the National Dam Safety Program and included the maintenance and update of the NID by USACE.

More recently, the NID was reauthorized as part of the Water Resources Reform and Development Act of 2014 and the Water Resources Development Act of 2018.

Information in the National Inventory of Dams

The NID consists of dams meeting at least one of the following criteria:

  1. High hazard potential classification - loss of human life is likely if the dam fails.
  2. Significant hazard potential classification - no probable loss of human life but can cause economic loss; environmental damage, disruption of lifeline facilities, or impact other concerns.
  3. Equal or exceed 25 feet in height and exceed 15 acre-feet in storage.
  4. Equal or exceed 50 acre-feet storage and exceed 6 feet in height.

The goal of the NID is to include all dams in the United States that meet these criteria, yet in reality, is limited to information that can be gathered and properly interpreted with the given funding.

The NID initially consisted of approximately 45,000 dams, which were gathered from extensive record searches and some feature extraction from aerial imagery. Since continued and methodical updates have been conducted, data collection has been focused on the most reliable data sources, which are the many federal and state government dam construction and regulation offices.

In most cases, dams within the NID criteria are regulated (construction permit, inspection, and/or enforcement) by federal or state agencies, who have basic information on the dams within their jurisdiction. Therein lies the biggest challenge, and most of the effort to maintain the NID; periodic collection of dam characteristics from 49 states (Alabama currently has no dam safety legislation or formal dam safety program), Puerto Rico, and 18 federal offices. USACE resolves duplicative and conflicting data from the 68 data sources, which helps obtain the more complete, accurate, and updated NID. Historically, the NID has been published every two years.  Starting in 2019, the NID will be updated annually.

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For any issues or questions regarding the NID, please contact the NID Data Team.