Dams by Hazard Level
Hazard potential classification for 92,625 dams in the National Inventory of Dams.
The hazard potential classification of a dam reflects the potential consequences of dam failure or improper operation — it does not indicate the probability that failure will occur or that the dam is currently unsafe. The classification system was developed by the U.S. Army Corps of Engineers and is used by state dam safety programs and federal regulators to prioritize inspection and maintenance resources.
Dams by Hazard Potential
Distribution of dams across the three hazard potential categories.
| Hazard Level | Dam Count | % of Total | Browse |
|---|---|---|---|
| Low | 60,343 | 65.1% | Browse |
| High | 16,894 | 18.2% | Browse |
| Significant | 11,360 | 12.3% | Browse |
| Undetermined | 4,027 | 4.3% | Browse |
| Not Rated | 1 | 0% | Browse |
Hazard potential is assigned by state dam safety engineers based on downstream conditions and potential failure consequences.
Dams by Condition Assessment
Current condition ratings for dams with available inspection data.
| Condition | Dam Count | % of Assessed | Browse |
|---|---|---|---|
| Not Rated | 36,831 | 49.3% | Browse |
| Satisfactory | 13,002 | 17.4% | Browse |
| Fair | 12,547 | 16.8% | Browse |
| Poor | 7,711 | 10.3% | Browse |
| Not Available | 3,540 | 4.7% | Browse |
| Unsatisfactory | 1,071 | 1.4% | Browse |
Condition assessments are based on the most recent inspection available. Many dams have not been recently inspected and may lack a condition rating.
The Three Hazard Potential Categories
High Hazard Potential
A dam classified as High hazard potential is one where failure is expected to cause loss of human life. This typically means there are homes, businesses, roads, or other infrastructure in the downstream flood inundation zone. High-hazard dams receive the most regulatory scrutiny, including more frequent inspections and stricter requirements for emergency action plans. The United States has 16,894 dams classified as High hazard potential.
Significant Hazard Potential
Significant hazard potential dams are those where failure could cause economic loss, environmental damage, or disruption of lifeline facilities — but where loss of life is not expected. This category typically applies to dams above rural roads, recreational areas, or environmentally sensitive lands.
Low Hazard Potential
Low hazard potential dams are those where failure would result in minimal economic or environmental losses, and loss of life is not anticipated. The downstream area is typically undeveloped or consists of agricultural land without residences. Despite the low hazard classification, these dams are still required to maintain structural integrity and are subject to periodic state inspection programs.
Condition vs. Hazard
Hazard potential and condition assessment are separate ratings. A dam can have High hazard potential (serious consequences if it fails) but be in Satisfactory condition (unlikely to fail). Conversely, a Low hazard dam in Poor condition may be structurally deficient but pose limited risk due to its remote location. Both ratings together give the most complete picture of dam risk.
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