Dam Failure

Dam failure or levee breeches can occur with little warning. Intense storms may produce a flood in a few hours or even minutes for upstream locations. Flash floods occur within six hours of the beginning of heavy rainfall, and dam failure may occur within hours of the first signs of breaching.

Other failures and breeches can take much longer to occur, from days to weeks, as a result of debris jams or the accumulation of melting snow.

There are more than 80,000 dams in the United States, according to the 2007 update to the National Inventory of Dams. Approximately one third of these pose a "high" or "significant" hazard to life and property if failure occurs.

Why Dams Fail

A "dam" is an artificial barrier that has the ability to impound water, wastewater, or any liquid-borne material for the purpose of storage or control of water. Dams can fail for one or a combination of the following reasons:

Overtopping caused by floods that exceed the capacity of the dam.
Deliberate acts of sabotage.
Structural failure of materials used in dam construction.
Movement and/or failure of the foundation supporting the dam.
Settlement and cracking of concrete or embankment dams.
Piping and internal erosion of soil in embankment dams.
Inadequate maintenance and upkeep.

Dam Failures in the United States

A series of dam failures in the 1970's caused the Nation to focus on inspecting and regulating dams.

On February 26, 1972, a tailings dam owned by the Buffalo Mining Company in Buffalo Creek, West Virginia failed. In a matter of minutes, 125 people were killed, 1,100 people were injured, and over 3,000 were left homeless.

On June 5, 1976, Teton Dam, a 123-meter high dam on the Teton River in Idaho, failed, causing $1 billion in damage and leaving 11 dead. Over 4,000 homes and over 4,000 farm buildings were destroyed as a result of the Teton Dam failure.

In November 1977, Kelly Barnes Dam in Georgia failed, killing 39 people, most of them college students.

The Next Major Dam Failure - The Johnstown Flood

At 4:07 p.m. on the afternoon of May 31, 1889, the residents of Johnstown, Pennsylvania heard a low rumble that grew to a "roar like thunder." After a night of heavy rains, the South Fork Dam had failed, sending tons of water crashing down the narrow valley.

Boiling with huge chunks of debris, the wall of flood water grew at times to 60 feet high, tearing downhill at 40 miles per hour and leveling everything in its path.

Thousands desperately tried to escape the wave. Those caught by the wave found themselves swept up in a torrent of oily, muddy water, surrounded by tons of grinding debris, which crushed some, provided rafts for others. Many became helplessly entangled in miles of barbed wire from a destroyed wire works.

Although it was over in 10 minutes, for some the worst was yet to come. Darkness fell, thousands were huddled in attics, others were floating on the debris, while many more had been swept downstream to the old Stone Bridge at the junction of the rivers. Piled up against the arches, much of the debris caught fire, entrapping forever 80 people who had survived the initial flood wave.

Most Recent Dam Failure

On the morning of December 14, 2005, a triangular section on the northwest side of the Missouri's Taum Sauk upper reservoir failed, releasing a billion gallons (4 million m³) of water in twelve minutes and sending a 20 foot (7m) crest of water down the Black River.

According to AmerenUE, a computer software problem caused the reservoir to continue filling even though it was already at its normal level. The water overtopped the walls, leading to the failure at 5:12 a.m. In addition, preliminary indications are that minor leakage through the dam walls over a prolonged period, had carried away fine material in the walls, weakening the reservoir's holding walls.

Piping ultimately creates voids in reservoir walls and causes reservoir walls to slump and fail. The failure of the reservoir occurred as the reservoir was being filled to capacity or may have possibly been overtopped.

What to Do Before a Dam Failure

Know Your Risk

Do you live downstream from a dam? Is the dam a high-hazard or significant-hazard potential dam? To find out, contact your state or county emergency management agency or visit the National Inventory of Dams (NID) or the Association of State Dam Safety Officials (ASDSO).

Once you determine that you live downstream from a high-hazard or significant-hazard potential dam and find out who owns the dam, this information also should be available from your state or county emergency management agency, NID, or ASDSO. See if a current EAP is in place for the dam.

An EAP is a formal document that identifies potential emergency conditions at a dam and specifies preplanned actions to be followed to reduce property damage and loss of life.

If there is a dam failure or an imminent dam failure and you need to evacuate, know your evacuation route and get out of harm's way.

In general, evacuation planning and implementation are the responsibility of the state and local officials responsible for your safety.

However, there may be situations where recreational facilities, campgrounds, or residences are located below a dam and local authorities will not be able to issue a timely warning. In this case, the dam owner should coordinate with local emergency management officials to determine who will warn you and in what priority.

During a Flood

If a flood is likely in your area, you should

Listen to the radio or television for information.
Be aware that flash flooding can occur. If there is any possibility of a flash flood, move immediately to higher ground. Do not wait for instructions to move.
Be aware of streams, drainage channels, canyons, and other areas known to flood suddenly. Flash floods can occur in these areas with or without such typical warnings as rain clouds or heavy rain.

If you must prepare to evacuate, you should do the following

Secure your home. If you have time, bring in outdoor furniture. Move essential items to an upper floor.
Take your important documents and your bug-out bag.
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.

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.
Six inches of water will reach the bottom of most passenger cars causing loss of control and possible stalling.
A foot of water will float many vehicles.
Two feet of rushing water can carry away most vehicles including sport utility vehicles (SUV’s) and pick-ups.

What to do after a Flood

The following are guidelines for the period following a flood

Listen for news reports to learn whether the community’s water supply is safe to drink.
Avoid floodwaters; water may be contaminated by oil, gasoline, or raw sewage. Water may also be electrically charged from underground or downed power lines.
Avoid moving water.
Be aware of areas where floodwaters have receded. Roads may have weakened and could collapse under the weight of a car.
Stay away from downed power lines, and report them to the power company.
Return home only when authorities indicate it is safe.
Stay out of any building if it is surrounded by floodwaters.
Use extreme caution when entering buildings; there may be hidden damage, particularly in foundations.
Service damaged septic tanks, cesspools, pits, and leaching systems as soon as possible. Damaged sewage systems are serious health hazards.
Clean and disinfect everything that got wet. Mud left from floodwater can contain sewage and chemicals.