Frequently Asked Questions

Questions

What is the hazard potential classification system for dams? What does it mean for a dam to be high hazard?
Is there a list of top high-hazard dams?
Is there a state by state list of deficient dams?
Are emergency action plans required?
What is the difference between a dam owner and a dam regulator?
What is the National Inventory of Dams (NID)?
What is the Infrastructure Report Card?

Public Safety and Low-Head Dams
What is a hydraulic jump or roller? How does it work and why is it dangerous? What happens if someone gets caught in one?
Why do low head dams exist?
Why don't we just remove all these dams?
What can I do to stay safe around a dam?
What can I do to help?



What is the hazard potential classification system for dams? What does it mean for a dam to be high hazard?

Common practice among federal and state dam safety offices is to classify a dam according to the potential impact a dam failure (breach) or mis-operation (unscheduled release) would have on upstream and/or downstream areas or at locations remote from the dam. The existing classification systems are numerous and vary within and between both the federal and state sectors. Although differences in classification systems exist, they share a common thread: each system attempts to classify dams according to the potential impacts from a dam failure or misoperation, should it occur. Most agencies use a variation on the following terminology:

High Hazard 
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.

Significant Hazard
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

Low Hazard
Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner’s property.



Is there a list of top high-hazard potential dams?

Due to security concerns, there isn't a list of the top high-hazard potential dams made available to the public. However, information about the number of high-hazard potential dams and regulations for each state can be found using the state map. If you are concerned about the safety of living near a dam, please visit livingneardams.org



Is there a state by state list of deficient dams?

Due to security concerns, there is not a list available of deficient dams. You can see the condition assessment data in aggregate for each state using the state map page or by visiting the National Inventory of Dams.



Are emergency action plans required?   

For state-regulated dams, it depends on the laws and regulations within each state. Some states require emergency action plans for high-hazard potential dams and some do not. As of 2016, 79 percent of state-regulated High-Hazard Potential dams have an EAP.  ASDSO's goal is 100 percent. Please visit the state pages for more information about individual state programs. 

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What is the difference between a dam owner and a dam regulator?

A dam owner is liable for the dam and is responsible for its upkeep, upgrade and repair. A dam regulator is responsible for enforcing policies, inspecting the safety of a dam, review of plans for new construction or rehabilitation and has a broader overall outlook on the construction and upkeep of dams. Owners can be private citizens or companies, quasi-governmental bodies, state or local governments or federal agencies. Regulators work for the state or federal government. Most dams - about 70% in the US - are regulated by state agencies. All states have regulatory programs in place except one, Alabama.  Federal agencies regulated about 14% of dams in the U.S. The remaining percentage are unregulated due to state or federal exemptions.



What is the National Inventory of Dams (NID)?

The U.S. Army Corps of Engineers maintains the National Inventory of Dams (NID) to help compile national data on dams in the United States. The NID lists over 90,000 dams. State and Federal regulatory agenices submit data to the NID.

The NID gives national and state by state information on the current state of dams. To be a part of the NID, the dam must either be: of high- or significant-hazard potential classification, equal or exceed 25 feet in height and exceed 15 acre-feet in storage or equal or exceed 50 acre-feet storage and exceed 6 feet in height.

To access the site visit: nid.usace.army.mil/



What is the Infrastructure Report Card?

The American Society of Civil Engineers (ASCE) released a Report Card for America’s Infrastructure every 4 years. The report card grades each facet of America’s Infrastructure in order to understand the funding required to address each issue, as well as to understand the overall condition and maintenance each facet already receives. As part of the report, ASCE considers the condition of dams and the state of regulatory and owner oversight.

ASCE considers America’s dams to be in poor to fair condition and that dam rehabilitation and safety should be of significant concern.

THe 2017 report card gave Infrastructure as a whole received a D+ while the conditions of dams received a D. Dams also received a D in 2013, the last time ASCE released a report.

To read the report on dams visit www.infrastructurereportcard.org/cat-item/dams/.


 

Public Safety and Low-Head Dams

What is a hydraulic jump or roller? How does it work and why is it dangerous? What happens if someone gets caught in one?

The boil, hydraulic jump, hydraulic roller, or simply hydraulic is a recirculating current that forms at and near dams. As water spills over the dam or down the spillway and into the river below, a current is created that spins anything caught in it in a circle, from the top of the water, back towards the dam, down along the bottom, and back up to the top. The current is extremely strong and hard to escape and is a leading cause of drowning deaths near dams. If someone gets caught in the current and is unable to escape it, they will recirculate, being tossed around until they are pulled from the current or the water pushes them away.

Much more information, including more detailed explanations of the way the hydraulic forms and flows, is available on the Public Safety Around Dams page and the Public Safety Hazards page.


 

Why do low head dams exist?

Low head dams serve a number of purposes. Historically, a low head dam was typically built to raise water levels upstream and regulate the flow of rivers to help water-powered mills run. While many of these mills no longer exist, the dams created for them still do. Other purposes include irrigation, electricity generation, water utilities, and upstream recreation. Although it is true that some dams no longer are needed to perform their original function, many other low head dams are still vital parts of our nation's infrastructure.


 

Why don't we just remove all these dams?

Removal of these dams is very expensive, and can often have very serious effects on the economy and environment in the surrounding area. Additionally, as stated before, many of these dams serve vital purposes in our infrastructure and cannot be removed. However, there are a number of ways that dams can be remodeled and retrofitted to make them more safe, including by adding new structures that break up the flow of water over the dam and eliminate some of the risks of creating a hydraulic roller. The decision to remove, remodel, or retrofit a dam is a difficult and intensive one that requires considerable study and financing to determine what the best plan of action is.

If you know of a dam you feel is a candidate for removal, remodelling, or retrofitting, it may benefit you to speak to your state dam safety agency.


 

What can I do to stay safe around a dam?

The most important thing to remember is keep your distance, keep your life. Steer clear of dam structures by recreating further up- or downstream, or portaging your kayak or canoe around the dam. Dams are not intended to be playgrounds, and pose many risks. Always be aware of your surroundings, know the location of dams, stay away from dams, and wear a personal floatation device such as a life jacket.


 

What can I do to help?

If you are interested in learning more about low head dam safety or getting involved, visit the Public Safety Around Dams page and get in touch with your state dam safety agency.

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