Living With Dams

Know Your Risks

FEMA P-956 / February 2013

Common

Beliefs 

About 

Dams

FICTION “The Army Corps of Engineers is responsible for most dams in the U.S.”

FACT State dam safety programs have 

oversight of most dams in the United 

States.

State agencies regulate more than 80% of

the Nation’s dams.

FICTION “Dams are like roads and bridges. The government takes care of them.”

FACT Most dams are privately owned. Dam owners are responsible 

for maintenance and upgrades.

Private dam owners are responsible for more than 65% of the Nation’s

dams. Many lack the financial resources necessary for adequate dam

maintenance.

FICTION “There are only a few dams in my State.”

FACT There are more than 84,000 dams in the United States (as 

of 2010). Most States are home to hundreds—or thousands—of 

dams, and each must meet regulatory criteria. 

•	 Texas has the most dams—more than 7,000—followed by Kansas

(6,087), Missouri (5,099), Oklahoma (4,755), and Georgia (4,606).

•	 Mississippi, North Carolina, and Iowa each have more than 3,000 dams.

•	 Five States—Alabama, Montana, Nebraska, South Carolina, and South

Dakota—each have more than 2,000 dams.

•	 Fifteen other States have more than 1,000 dams each.

•	 Delaware has the fewest number of dams, with 86.

FICTION “That dam has been here for years—it’s not going anywhere.”

FACT Advancing age can make dams more susceptible to failure. 

The average age of dams in the United States is more than 53 years.

As dams get older, deterioration increases and repair costs rise. Some

common problems of older dams are:

•	 Deteriorating metal pipes and structural components; metal rusts over

time, and after 50 years it can fail completely.

•	 Sediment-filled reservoirs. Some sediment may have contaminants from

chemicals in runoff from upstream.

•	 Runoff from subdivisions and businesses built upstream. Roofs and

concrete streets and sidewalks increase the volume of runoff to the

reservoir.
Ask yourself this:

Could my life and property 

be affected by a nearby dam? 

Dams provide drinking water, hydroelectric or water power, 

flood control, recreation, and many other benefits to 

people and local economies. But if they fail, dams can pose 

significant risks to people and property downstream. 

There are dams in every State. It is important to know if you 

and your loved ones live, work, or play in areas that may be 

affected by a dam and what to do if one fails. 

This booklet was created to help answer questions about 

dams: what purposes they serve, what risks are associated 

with dams, and where you can get information about how to 

react if you are affected by a dam.
Living with Dams: Know Your Risk 1

Why should I care 

about dams?

Although dam failures are infrequent, the impacts can be 

catastrophic, often far exceeding typical stream or river 

flood events.

What Dams Provide

Dams are assets, but they can also be 

hidden liabilities.

Dams provide vital benefits, including flood 

protection, water supply, hydropower, irrigation, 

and recreation. Imagine the impact of losing a 

major reservoir or flood control dam.
2 Living with Dams: Know Your Risk

•	 Would there be catastrophic flooding? How many homes and businesses 

might be flooded? How many people would be displaced?

•	 Would there be adequate water for domestic use? Irrigating crops? Caring 

for livestock? Fighting fires? 

•	 Are local utilities dependent on hydropower? How many lives and jobs 

would be affected by temporary shutdown or closure of an industry 

dependent on hydropower? 

•	 How would transportation systems—roads, railroads, navigable 

waterways—be affected? 

•	 How would local economies, jobs, and areas dependent on recreation be 

affected if a reservoir is lost?

If they are not maintained 

and operated correctly, dams 

can pose risks to those living 

downstream. When dams age, 

deteriorate, or malfunction, they 

can release sudden, dangerous flood 

flows. Dam failures can pose safety 

risks to an often unaware public.

Many communities in the United 

States are in the vicinity of at least 

one dam. In many cases, large 

populations, vital elements of our 

infrastructure, jobs, and businesses 

are located downstream of dams. 

Dam failure floods are almost 

always more sudden and violent 

than normal stream, river, or coastal 

floods. They often produce damage 

that looks like tornado damage.

Dams are owned and operated by 

many different types of owners. 

Sometimes they serve a limited 
Living with Dams: Know Your Risk 3

purpose—for instance, a neighborhood association that wants its homes 

built around a lake—and sometimes they serve larger interests—for 

instance, a water supply utility. 

Downstream development increases the potential consequences of a dam’s 

failure. Dams built in once rural areas that would have affected nothing but 

open fields if they failed, are now capable of affecting neighborhoods and 

industrial areas. As a result of both new dam construction and development 

downstream of existing dams, the number of dams that could pose a risk to 

human life if they fail is steadily increasing. In the last decade, that number 

has increased by over 1,000 to a total of about 14,000 dams.

•	 Any dam has the potential to adversely affect 

downstream areas and lives; and

•	 Many dams, should they fail, can also affect the 

delivery of essential utilities or flood control.
4 Living with Dams: Know Your Risk

Facts About Dams

Purposes

The purpose of a dam is to retain or store 

water or other liquid-borne materials for 

any of several reasons, such as human water 

supply, irrigation, livestock water supply, 

energy generation, containment of mine 

tailings, recreation, and pollution or flood 

control. Many dams fulfill a combination 

of these functions.

Ownership

Dams are unique components of our 

infrastructure because most dams are 

privately owned. 

Dam owners are solely responsible for 

keeping their dams safe. Owners must 

finance maintenance, repairs, and 

upgrades, which can be expensive. Costs 

for non-Federal dam rehabilitation projects 

commonly range from hundreds of 

thousands to millions of dollars per dam. 

Such high price tags place a huge burden 

on dam owners, many of whom cannot 

afford to maintain their dams. 

Regulation

Dams are regulated for safety by the 

government in much the same way as 

bridges, factories, etc. States regulate the 

majority of dams in the United States 

(about 80 percent); the Federal government 

regulates the remaining 20 percent.

U.S. Dam Owners
Living with Dams: Know Your Risk 5

Main Types 

of Dams

Manmade dams may be classified by 

the type of construction material used, 

the methods used in construction, the 

slope or cross-section of the dam, the 

way the dam resists the forces of the 

water pressure behind it, the means 

used for controlling seepage, storage 

characteristics (on a watercourse, offstream, above or below ground level), 

and occasionally, according to the 

purpose of the dam. 

Dams can be constructed from a variety 

of materials, including soil, rock, tailings 

from mining or milling, concrete, 

masonry, steel, timber, miscellaneous 

materials (such as plastic or rubber), and 

combinations of these materials.

Embankment dams are the most 

common type of dam in use today. 

Materials used for embankment dams 

include natural soil or rock or waste 

materials obtained from mining or 

milling operations. An embankment 

dam is termed an “earthfill” or “rockfill” 

dam, depending on whether it comprises 

compacted earth or mostly compacted 

or dumped rock. The strength of an 

embankment dam is primarily a result 

of the type of materials from which the 

dam is made.

Dams by Primary Purpose

Embankment dam
6 Living with Dams: Know Your Risk

Concrete dams may be 

categorized as gravity and 

arch dams depending on 

how they resist water pressure 

from the reservoir. The most 

common type of concrete dam 

is a concrete gravity dam. The 

mass weight of concrete and 

friction resist the reservoir 

water pressure. A buttress dam 

is a specific type of gravity 

dam in which the large mass 

of concrete is reduced, and the water pressure forces are diverted to the 

dam foundation through vertical or sloping buttresses. Gravity dams are 

constructed of vertical blocks of concrete with flexible seals in the joints 

between the blocks.

Concrete arch dams are typically thinner in cross-section than gravity dams. 

The reservoir water forces acting on an arch dam are carried laterally into 

the abutments. The shape of the arch may resemble a segment of a circle 

or an ellipse, and the arch may be curved in the vertical plane as well as the 

horizontal plane. Such dams are usually constructed of a series of vertical 

blocks that are keyed together; barriers to stop water from flowing are 

provided between the blocks. Variations of arch dams include multi-arch 

dams, in which more than one curved section is used, and arch-gravity dams, 

which combine some features of the two types of dams.

Concrete dam

Other Types of Dams

Tailings dams impound industrial waste materials from mining operations 

or mineral processing.

Ash impoundments, or ponds, are used to store or dispose of ash generated 

primarily from the combustion of coal. These impoundments are a type of 

waste management facility consisting of an excavated, dammed, or diked 

reservoir in which coal ash is stored for future removal or disposed of as 

slurry or sludge. The coal ash solids settle out, and the water at the surface 

is discharged through a designed and managed outlet structure to a nearby 

stream, surface water, or plant process water system. 
Living with Dams: Know Your Risk 7

Spillway Discharge and Seepage

Water may pass from the reservoir to the downstream side of a dam by: 

•	 Passing through the main spillway or outlet works 

•	 Passing over an auxiliary spillway 

•	 Overtopping the dam 

•	 Seeping through a dam or abutment, or under a dam

Water normally passes through the main spillway or outlet works; it should 

pass over an auxiliary spillway only during periods of high reservoir levels 

and high water inflow. 

A number of concrete dams have been designed to be overtopped. 

However, overtopping of an embankment dam is detrimental because the 

embankment materials may be eroded.

All embankment and most concrete dams have some seepage; controlling 

the seepage using proper dam construction, maintenance, and monitoring is 

important to prevent internal erosion and instability. 

Release of Water

Intentional releases of water from dams are confined to spillways and outlet 

works. A dam typically has a principal or mechanical spillway and a drawdown 

facility. Additionally, some dams are equipped with auxiliary spillways to safely 

pass extreme floods.

Even when operated as designed, many dams will pass huge volumes of flood 

water into downstream areas.

Spillways are designed to prevent overtopping of dams. The most 

common type of spillway is the free-overflow spillway. This spillway may be 

constructed over or through the dam or an abutment. To permit maximum 

use of storage volume, movable gates are sometimes installed above the 

spillway crest to control discharge. Many smaller dams have a pipe and 

riser spillway to carry most flows and a vegetated earth or rock-cut spillway 

through an abutment to carry infrequent high flood flows. In dams such as 

those on the Mississippi River, flood discharges are of such magnitude that 
8 Living with Dams: Know Your Risk

Parts of a dam

the spillway occupies the entire width of the dam and the overall structure 

appears as a succession of vertical piers supporting movable gates. High archtype dams in rock canyons usually have downstream faces too steep for an 

overflow spillway. In Hoover Dam on the Colorado River, for example, a shaft 

spillway is used. In shaft spillways, a vertical shaft upstream from the dam 

drains water from the reservoir when the water level becomes high enough 

to enter the shaft or riser; the vertical shaft connects to a horizontal conduit 

through the dam or abutment into the river below.

Outlet Works In addition to spillways, dams contain outlet works that allow 

water to be drawn, either continuously or as needed, from the reservoir, and 

provide a way to draw down the reservoir for repair or safety concerns. Water 

may be discharged into the river below the dam, run through generators 

to provide hydroelectric power, or used for irrigation. Dam outlets usually 

consist of pipes, box culverts, or tunnels with intake inverts near the 

minimum reservoir level. Such outlets are provided with gates or valves to 

regulate the flow rate.
Living with Dams: Know Your Risk 9

What are the risks 

associated with dams?

Dam failures are low probability but high consequence events. 

Even so, they typically occur somewhere in the United States 

every year.

Although thousands of lives have been lost and substantial property damage 

has occurred as a result of dam failure, good planning and improved dam 

safety programs, as advocated in this brochure, have reduced loss of life and 

property damages dramatically in recent years.

Dam failures or partial failures are not usually caused by storm events. Most 

failures fall into one or more of the following categories: 

Structural failures Foundation defects, including settlement and slope 

instability, or damage caused by earthquakes, have caused about 30 percent 

of all dam failures in the United States.

Mechanical failures Malfunctioning gates, conduits, or valves can cause dam 

failure or flooding both upstream and downstream and account for about 36 

percent of all dam failures in the United States.

Hydraulic failures Overtopping of a dam is often a precursor to dam failure. 

National statistics show that overtopping due to inadequate spillway design, 

debris blockage of spillways, or settlement of the dam crest accounts for 

approximately 34 percent of all dam failures in the country.

These problems can lead to dam failure:

•	 Inadequate design criteria

•	 Malfunction of dam components

•	 Spillway damage or malfunction

•	 Seepage problems

•	 Embankment 

stability problems

•	 Damage from vandalism

•	 Improper operation
10 Living with Dams: Know Your Risk

Thousands of dams nationwide are considered deficient and susceptible to 

failure because of these problems.

Planned Releases

Operation of spillways, either planned or in response to emergency 

situations, can create flooding and public safety hazards, even in the absence 

of a dam failure. During periods of extreme flow, dams may fill to capacity, 

necessitating emergency releases that can flood downstream areas. People 

swimming and fishing downstream of dams have been caught in spillway 

releases, at times with tragic results. Many dams incorporate sirens to warn 

the public of an impending release.

Recent Dam Failures

July 25, 2010 – Lake Delhi Dam, Delaware County, IA

The dam failure drained a 9-mile recreational lake and damaged or 

destroyed up to 300 homes.

January 6, 2009 – Private Dam, Etowah County, AL

After floodwaters washed away a culvert, a private dam broke and produced 

up to 12 feet of flooding in the area, which caused residences to be 

evacuated. A dozen roads were also closed as a result of floodwaters and 

property damage was reported to be $100,000.

December 22, 2008 – Kingston Coal Waste Dam, Roane County, TN

The Kingston Dam was a 40-acre pond used by the Tennessee Valley 

Authority to hold a slurry of ash generated by the coal-burning Kingston 

Steam Plant. The dam gave way just before 1 a.m., burying a road and 

railroad tracks leading to the plant under 5.4 million cubic yards (more than 

1 billion gallons) of sludge, which damaged 12 homes and covered hundreds 

of acres. The cleanup cost was $1 million per day. 

March 14, 2006 – Ka Loko Dam, Kauai, HI  

The failure of an embankment dam in this relatively undeveloped area 

killed seven people and caused extensive environmental damage.
Living with Dams: Know Your Risk 11

December 14, 2005 – Taum Sauk Dam, Lesterville, MO  

The failure of this off-stream hydropower facility located high above 

Johnson’s Shut-Ins State Park destroyed the home of the park superintendent 

and swept his family downstream. Miraculously, all survived. The flood 

washed out part of a State road and caused extensive environmental damage 

to the East Fork of the Black River and to the park, which in warm weather 

months is typically populated with hundreds of campers and hikers.

Historically Significant Dam Failures

February 26, 1972 – Buffalo Creek Valley, WV  

The failure of a coal-waste impoundment at the valley’s head took 125 lives 

and caused more than $400 million in damages, including the destruction 

of over 500 homes. This disaster wiped out 16 communities.

June 9, 1972 – Rapid City, SD

The Canyon Lake Dam failure took an undetermined number of lives 

(estimates range from 33 to 237). Damages, including the destruction of 

1,335 homes, totaled more than $60 million.

June 5, 1976 – Eastern Idaho

Eleven people perished when Teton Dam failed. The failure caused an 

unprecedented amount of property damage totaling more than $1 billion. 

The failure flooded at least six communities and tens of thousands of acres.

July 19–20, 1977 – Laurel Run, PA

Laurel Run Dam failed, killing more than 40 people and causing $5.3 

million in damages.

November 5, 1977 – Toccoa Falls, GA

Kelly Barnes Dam failed, killing 39 students and college staff and causing 

about $2.5 million in damages.

May 31, 1889 – Johnstown, PA

The deadliest dam failure in U.S. history took the lives of more than 

2,200 people.
12 Living with Dams: Know Your Risk

Am I or could I be affected by 

a dam and what area would 

flood if the dam failed?

Many people who live in dam breach inundation zones are 

completely unaware of the potential hazard lurking upstream.

The “inundation zone” is the area downstream of 

the dam that would be flooded in the event of a 

failure (breach) or uncontrolled release of water, 

and is generally much larger than the area for the 

normal river or stream flood event.

The “dam breach inundation zone” is larger 

than the 1-percent-annual-chance flood used on 

FEMA’s Flood Insurance Rate Maps (FIRMs).
Living with Dams: Know Your Risk 13

RED = More than 1,000 dams

YELLOW = Between 500 and 1,000 dams

BLUE = Between 100 and 500 dams

GREEN = 100 dams or less

Number of high- and significanthazard potential dams, i.e., those 

that have the potential to cause loss 

of life (high) or extreme property 

damage (significant) if they fail. 

NOTE: 

Since Alabama is the only State that does not have a 

regulatory program, the number of reported dams may be low.

How do I find out if I live in a dam breach inundation zone?

•	 Contact your local emergency management agency (a simple Internet 

search will most likely locate the appropriate office).

•	 Contact your State dam safety program (see the U.S. map at 

www.damsafety.org). 
14 Living with Dams: Know Your Risk

Before buying: 

Do some research, Know the facts

Before buying a home or business, determine whether it is in a dam breach 

inundation zone. This determination is the buyer’s responsibility.

Prospective buyers should know whether there is an existing upstream dam 

or the potential for an upstream dam to be built. This is sometimes difficult 

to determine while standing on the property because the upstream dam may 

not be in sight. In some cases, the dam site may be several miles upstream 

of the property and the view may be 

obscured. Here are some resources that 

will assist your research:

•	 7.5 minute U.S. Geological Survey 

topographic maps: 

http://topomaps.usgs.gov

•	 Google Earth

•	 The State dam safety agency office, 

the local emergency management 

office, or the local soil and water 

district office

Likewise, buying property on or 

near a manmade lake requires an 

understanding of what that proximity entails. Such properties tend to have 

higher values than similar sized properties not associated with a lake. The 

removal of the lake or a permanent lowering of the lake’s water level can 

dramatically reduce property values on or near the lake. The fluctuation 

of the lake levels from normal pool to flood pool elevations can hinder or 

eliminate the use of the property and associated structures. In many cases 

the dam is owned by a neighborhood association of lakeside property owners 

who are responsible for the dam’s maintenance and are liable for any risk 

posed by the dam.

Prospective buyers should learn of the risks, legal and financial liabilities, 

and other issues associated with the lake, dam, and control structures prior 

to the purchase of a home.

SOURCE: GOOGLE EARTH
Living with Dams: Know Your Risk 15

Changing weather 

patterns, erosion, and 

development can affect 

areas at risk from 

dam failure. FEMA 

is currently updating 

and modernizing its 

FIRMs (www.fema.

gov/hazard/map/

firm.shtm) to help 

the public better 

understand flood risk. 

FEMA has published 

almost 100,000 

individual FIRMs. You 

can find your map 

and learn how to read 

it so you can make 

informed decisions 

about protecting 

your property, both 

financially and 

structurally at the 

FEMA Map Service 

Center (www.msc.fema.gov). 

Currently, the dam breach inundation zones are NOT shown on Flood 

Insurance Rate Maps maps as areas requiring flood insurance. 

Even though it is not required, buying flood insurance to protect a 

financial investment in homes and businesses located below dams 

may be wise.

Visit www.FloodSmart.gov for more information on flood insurance.
16 Living with Dams: Know Your Risk

Once I determine that my 

property is in a dam breach 

inundation zone, what’s next?

Find out the dam’s condition. Does it meet Federal or State 

safety criteria?

Contact your county emergency management 

coordinator or State dam safety program office 

to find out who owns the dam and which agencies 

regulate it. Contact information for State Dam 

Safety Programs is listed online at 

www.damsafety.org.
Living with Dams: Know Your Risk 17

Ask questions about the dam’s

condition and hazard potential

State officials and the dam owner should be able to answer questions 

such as:

•	What is the dam’s hazard potential classification?

•	When was it last inspected?

•	What is its condition?

•	Is the owner financially capable of properly maintaining the dam?

•	Is there a plan in place in the event of a dam failure?

Emergency Action Plans

One of the most important questions to ask State dam safety officials or dam 

owners is whether there is an up-to-date Emergency Action Plan (EAP) for 

the dam in question. An EAP is a formal document that identifies potential 

emergency conditions at a dam and specifies actions to reduce property 

damage and loss of life. The EAP includes actions the dam owner should 

take to mitigate problems at the dam and issue warnings to responsible 

emergency management authorities.

If you live or work in a dam breach inundation zone, find out your 

evacuation route so that you can quickly get out of harm’s way in the event 

of a dam incident. To obtain this information, contact your State and 

local emergency management officials, who are responsible for evacuation 

planning and implementation.

Communication with emergency managers is key. 

Points to remember:

•	 Find out if there is an up-to-date EAP for the dam.

•	 Determine what types of warning systems are in place to warn residents 

of a dam incident. For example, are there sirens, a Reverse-911 phone 
18 Living with Dams: Know Your Risk

messaging system, bullhorns, or door-to-door warning procedures in 

place? Always heed warnings to leave.

•	 Find out how to get to a place of safety and what evacuation routes will 

be open.

•	 Ask about the location of community emergency shelters.

•	 Inform emergency management officials of family members who are 

handicapped or may need special assistance.

Prepare your home and your family

•	 Inform your family of dam failure flood risks, and make sure each family 

member knows what to do in the event of an emergency.

•	 Elevate your furnace, water heater, and electric panel if they are 

susceptible to flooding.

•	 Install “check valves” in sewer traps to prevent floodwater from backing up 

into drains.

•	 Seal basement walls with waterproofing compounds to avoid seepage.

•	 Keep valued possessions and important papers on an upper level of your 

home or in a safety deposit box.

•	 Prepare an emergency kit.

What should you do in the event of an emergency? 

If a flood is likely in your area, you should:

•	 Listen to the radio or television for information.

•	 Be aware that dam failure or operational flooding can occur. If there is 

any possibility of a flash flood, move immediately to higher ground. Do not 

wait for instructions to move. Get to high ground if flooding is imminent.

•	 Be aware of streams, drainage channels, canyons, and other areas that may 

flood suddenly. Flash floods can occur in these areas with or without such 

typical warnings as rain clouds or heavy rain.
Living with Dams: Know Your Risk 19

If you must prepare to evacuate, you should:

•	 Secure your home. If you have time, bring in outdoor furniture. Move 

essential items to an upper floor.

•	 Turn off utilities at the main switches or valves if instructed to do so. 

Disconnect electrical appliances. Do not touch electrical equipment if you 

are wet or standing in water.

If you have to leave your home, remember these 

evacuation tips:

•	 Do not walk through moving water. Six inches of moving water can make 

you fall. If you have to walk in water, walk where the water is not moving. 

Use a stick to check the firmness of the ground in front of you.

•	 Do not drive into flooded areas. If floodwaters rise around your car, 

abandon the car and move to higher ground if you can do so safely. You 

and the vehicle can be quickly swept away.

Do I need to buy flood insurance?

Because standard homeowners insurance doesn’t cover flooding, 

it’s important to have protection from the floods associated with 

hurricanes, tropical storms, heavy rains, dam failures, and other 

conditions that can affect your home or business.

In 1968, Congress created the National Flood Insurance Program 

(NFIP) to help property owners to financially protect themselves from 

floods. The NFIP offers flood insurance to homeowners, renters, 

and business owners if their community participates in the NFIP. 

Participating communities agree to adopt and enforce ordinances that 

meet or exceed FEMA requirements to reduce the risk of flooding. 

Flood insurance is highly recommended but not required for those 

living in dam breach inundation zones.

Just because you haven’t experienced a flood in the past doesn’t mean 

you won’t in the future. Flood risk isn’t based just on history. It’s also 

based on a number of other factors: potential dam failure, rainfall, 

river-flow, topography, flood control measures, and changes due to 

development.
20 Living with Dams: Know Your Risk

Dam Safety, Flood Risk, and 

Emergency Management 

Responsibilities

The Public

•	 Understand that you are at risk and that there are steps you can take now 

to protect yourself from floods should a dam fail or release flood waters.

•	 Know your evacuation routes.

Dam Owners and Operators

•	 Maintain and operate the dam properly to ensure that the dam does 

not fail. 

•	 Work with State and local officials to mitigate the consequences of 

dam incidents.

•	 Maintain an EAP. Inform local officials of risks associated with the dam.

•	 Work with the Federal or State regulator to comply with safety standards.

State and Local Governments

•	 State governments are responsible for public safety regulation for more 

than 80 percent of the Nation’s dams (non-Federal dams).

•	 State and local governments are responsible for determining how land is 

used in floodplains and for enforcing floodplain management regulations.

•	 Local governments are responsible for emergency response and evacuation 

in a flooding situation.
Living with Dams: Know Your Risk 21

What is the 

1-percent-annual-chance flood?

FEMA uses the 1-percent-annual-chance flood standard (the flood 

that has a 1 percent annual chance of being equaled or exceeded) 

to define floodplain boundaries on FIRMs, which are used for 

insurance purposes, floodplain management, and planning efforts. 

Areas within the 1-percent-annual-chance floodplain are known as 

Special Flood Hazard Areas (SFHAs).

•	Within an SFHA, you have a 26 percent chance of experiencing 

a flood of that magnitude or greater during the life of a 30-year 

mortgage. You would have a 4 percent chance of experiencing 

a fire during the same period of time.

•	Dam breach inundation zones may far exceed the 1 percent 

flood zones mapped by FEMA.

•	Floods greater than a 1-percent-annual-chance flood can and 

do happen; the Midwest experienced two 0.2-percent-annualchance floods in a 15-year period (in 1993 and 2008). 

•	Dam failure floods are almost always more violent than the 

normal stream, river, or coastal floods.
22 Living with Dams: Know Your Risk

Federal Dam Safety, Floodplain, and 

Emergency Management Programs

•	 Several Federal agencies have built or own dams, including the U.S. 

Army Corps of Engineers, the Department of the Interior, the Tennessee 

Valley Authority, and the Department of Agriculture. Collectively, the 

Federal Government owns 3,225 dams (2010 data). The Department of 

Agriculture’s Natural Resources Conservation Service helped build more 

than 11,000 dams now owned by local watershed districts.

•	 Some Federal agencies, including the Federal Energy Regulatory 

Commission (FERC) and the Mine Safety and Health Administration 

(MSHA), regulate privately owned dams. According to the National 

Inventory of Dams, 

FERC and MSHA 

collectively regulate 

more than 2,200 dams 

(2010 data).

•	 FEMA provides 

Federal, State, and 

local governments 

with valuable data for 

assessing and reducing 

flood risks to people 

and their homes and 

businesses. 

•	 FEMA analyzes and identifies the 

flood hazards near levees and 

dam breach inundation zones 

and helps communities identify 

the risks associated with levees 

and dams.

•	 FEMA does not own, operate, 

maintain, or certify dams or 

levees for safety.
Living with Dams: Know Your Risk 23

RESOURCES for Citizen Involvement

Association of State Dam Safety Officials:

www.damsafety.org

Dam Safety Action:

www.damsafetyaction.org

National Dam Safety Program:

www.fema.gov/plan/prevent/damfailure/ndsp.shtm

National Inventory of Dams:

http://nid.usace.army.mil

American Society of Civil Engineers Infrastructure Report Card – Dams:

www.infrastructurereportcard.org/fact-sheet/dam

FEMA FloodSmart: 

www.floodsmart.gov

USDA Natural Resources Conservation Service Watershed Rehabilitation 

Information:

www.nrcs.usda.gov/wps/portal/nrcs/main/national/programs/landscape/wr

National Weather Service, River Observations and Forecasts:

http://water.weather.gov/ahps/

The National Emergency Management Association: 

www.nemaweb.org

The International Association of Emergency Managers: 

www.iaem.com

Find out more about the maps used to determine flood risk:

National Flood Insurance, Program Customer Service

888-379-9531

TTY: 800-427-5593

Fax: 202-646-2818

E-mail: FloodSmart@dhs.gov

Mail: FEMA, 500 C Street SW, Washington, D.C. 20472 

Contacting FEMA: 

For a comprehensive list of contact information, please see the FEMA Web 

site: www.fema.gov

FEMA publishes maps indicating a community’s flood hazard areas and 

the degree of risk in those areas. Flood insurance maps are usually on file 

in a local repository in the community, such as the planning and zoning or 

engineering offices in the town hall or the county building. 

In addition, you can order maps online or by writing, telephoning, or faxing a 

request to the FEMA Map Service Center: www.msc.fema.gov, P.O. Box 3617 

Oakton, Virginia 22124-9617 Tel: (877) 336-2627 Fax: (703) 212-4090 

E-mail: MSCservices@riskmapcds.com
24 Living with Dams: Know Your Risk

Public Safety

Aside from the possibility of floods due to dam failure, dams also pose risks to 

swimmers, fishermen, and boaters.

Small dams, also known as low-head dams, “killer dams,” or “drowning 

machines,” are deceptively dangerous. These dams are especially dangerous 

to swimmers and boaters because they are often hard to see, especially 

from the upstream side. Boaters who go over a 

low-head dam are often trapped in a submerged 

hydraulic jump or “roller” formed just below the 

dam. Likewise, swimmers and fishermen who get 

too close to dams can be caught in this dangerous 

circulating current.

Hundreds of people have been killed at low-head 

dams, but few States regulate these dangerous 

structures. 

Stay safe around dams

SOURCE: Ontario Ministry of Natural Resources Web site, 2012.

Summer

•	 Always stay outside booms and away from all 

dam structures. 

•	 Never swim above a dam or dive from a dam 

structure. Currents can pull you through the 

dam or pull you against flow structures with 

such force that you cannot escape.

•	 Never fish, boat, or swim below a dam. Water 

levels and flows can change very quickly, and 

you may not be able to react in time to avoid 

the danger.

•	 Never moor, tie, or anchor your boat below 

a dam. Always keep personal watercraft and 

boats clear of dams. 

•	 Never sunbathe, picnic, or camp in an area that 

may flood as a result of dam operations.
Living with Dams: Know Your Risk 25

Autumn

•	 Be aware of possible changes in water flows or 

levels from dam operations when operating 

an All-Terrain Vehicle (ATV). ATVs should be 

used with caution around water.

•	 Always obey posted signs, and do not enter 

fenced areas to hike or access hunting or 

nature viewing areas.

Winter

•	 Beware of thin ice that may develop as a result 

of dam operations. 

•	 Never venture out on the ice alone. Always wear 

a life jacket and carry a throw rope.

•	 Always be aware of the potential for slush 

under the snow when venturing out on the ice. 

Dam operations often result in lowering of 

water levels throughout the winter and spring. 

However, this can result in ice collapsing onto 

lower water levels and then water seeping up 

under the snow. Travel in slush conditions is 

very difficult regardless of the mode of travel.

Spring

•	 Stay clear of dams when fishing. Water flows 

and levels can change quickly. 

•	 Always stay clear of dams when canoeing 

and kayaking.

General

•	 Stay off the dam structures unless the area is 

clearly marked for public travel.

•	 Be alert to changes in water levels.


FEMA P-956

Catalog No. 13052-3