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

1) High hazard classification - loss of one human life is likely if the dam fails, 2) Significant hazard classification - possible loss of human life and likely significant property or environmental destruction, 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 U.S. that meet these criteria, yet in reality, is limited to information that can be gathered and properly interpreted with the given funding. The Inventory 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. The Corps resolves duplicative and conflicting data from the 68 data sources, which helps obtain the more complete, accurate, and updated NID.

If you have any questions or concerns regarding your account, please contact the NID Data Team at: nid@usace.army.mil.

See NID codes here: http://geo.usace.army.mil/pgis/f?p=397:6:0::NO