Dams

Condition & Capacity

Dams are present in all 50 states, serving a wide range of daily needs, such as water storage, irrigation, hydropower, mining, flood control, and recreation. The public most commonly thinks of engineering marvels like the Hoover Dam in Nevada, which provides water supply and hydroelectric power to Arizona, Nevada, and California. However, only 3% of dams are currently a source of hydroelectric energy. 

Dams are classified by regulatory agencies based on their hazard potential or anticipated downstream consequences in the event of failure. The failure of a dam that is classified as high-hazard-potential is anticipated to cause a loss of life. As of 2019, there are approximately 15,600 dams in the United States that are classified as high-hazard structures. Over the last 20 years, the number of high-hazard-potential dams has more than doubled as development steadily encroaches on once-rural dams and reservoirs. Meanwhile the number of dams classified as significant-hazard-potential, meaning a failure would likely cause significant economic damage, but not necessarily the loss of life, reduced during this period from 11,882 in 2017 to 11,343 dams in 2019. 

Another contributing factor to the shift in the classification of dams is increases in state funding for dam safety programs. With state dam safety programs better able to assess these structures, the opportunity for owners to become aware of rehabilitation, repair, or removal needs increases, as does the likelihood of dams being classified as high hazard potential. Signs of improved funding began as early as 2015 as state economies began to recover from the 2008 recession. Approximately 69% of dams in the National Inventory of Dams (NID) maintained by the U.S. Army Corps of Engineers are state-regulated dams. 

Recent crises following heavy seasonal rains, like the failure of the Oroville Dam spillway in 2017 or the failure of the Edenville and Sanford dams in Michigan, have made major headlines, highlighting the poor condition of many of the nation’s dams. Thankfully, incidents of large-scale flooding such as these are rare. Proper maintenance, routine inspection, necessary upgrades, and implementation of an Emergency Action Plan can ensure optimal conditions, which in turn protect the public health, safety, and welfare. 

The average age of our nation’s dams is 57 years. By 2030, seven out of 10 dams in the United States will be over 50 years old. While this is not a reflection on hazard potential, the high average age means that the majority of dams will not have been built to current standards, let alone incorporate newer standards that improve their resilience and reduce the risk to downstream areas. Furthermore, at the time of their construction, they may have been considered low hazard potential, so they may not be able to withstand the increasingly frequent and severe weather events or other natural hazards like earthquakes. 

A secondary classification applied to any dam refers to its condition rating based on structural safety. In the NID, dams can range from “not rated,” which refers to either the lack of inspection or lack of rating, to “satisfactory,” indicating no existing or potential dam safety deficiencies. States and federal agencies may have additional definitions and rating applications that are used to classify dams. Definitions may vary slightly from state to state as well as among federal agencies.