Dams: History, anatomy and common reasons for failure

By Chaffin Mitchell, AccuWeather staff writer

Dams date back to around 2950-2750 B.C., when the ancient Egyptians built the first known dam, but people might not understand the ins and outs of what makes a dam a success or failure.

Dams are massive barriers built across rivers and streams to confine and utilize the flow of water for human purposes such as irrigation and generation of hydroelectricity.

Hydropower is a form of renewable energy that uses the water stored in dams and from rivers to generate electricity.

Unfortunately, there are also some problems that can arise from dams. While it is rare, dams can fail and create catastrophic flooding and lead to loss of lives and property.

In February 2017, Oroville Dam was damaged, prompting the evacuation of more than 180,000 people living downstream. Heavy rainfall damaged the main spillway, then rain raised the lake level until it flowed over the emergency spillway.

As water flowed over the emergency spillway, officials were worried a a 30-foot wall of water would push into the Feather River below and flood communities downstream. No collapse occurred, but the water further damaged the main spillway and eroded areas of the emergency spillway.

"Thankfully, total failures of dams are not a common occurrence. What is more common are 'component failures,' where an incident occurs with a feature or system of the dam," Communications Manager, Association of State Dam Safety Officials, Inc. Katelyn Riley said.

Drought Colorado River

The low level of the water line is shown on the banks of the Colorado River at the Hoover Dam in Hoover Dam, Ariz. U.S. (AP Photo/Ross D. Franklin, File)

Riley said some examples of component incidents include broken concrete or severely rusted pipe spillways that have deteriorated and failed over time; failed electrical or mechanical systems; cracked and slumped earthen embankments; and sinkholes in the earthen embankment.

"Total dam failures are often a combination of deficiencies in design, aging and deterioration, or multiple component failures, coupled with an extreme loading event such as a flood or an earthquake," Riley said.

Some dams are aging and were constructed before today’s safety standards were in place.

"These dams may have inadequate spillway capacity to handle severe storms and can become overwhelmed with flow going over the top of the dam. This can result in severe 'overtopping' erosion and failure of the dam," Riley said.

There are some common factors and features that help to ensure that dams are safe and don't fail.

"Current designs for dams look to analyze the types of loading events a dam may encounter such as a severe flood or an earthquake and make certain that it has adequate spillway size or structural stability to withstand that type of event," Riley said.

According to Riley, this may require enlarging or fortifying a spillway chute or gate. It may require reinforcing the structure and embankment to provide additional stability.

"Uncontrolled seepage can be another common failure mode so internal filters and/or foundation cutoffs can be design features to help prevent internal erosion," Riley said.

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"Well-equipped and well-staffed state dam safety programs, and the routine visual inspections required by such programs, are a critical factor in the dam safety initiative, but dams are the responsibility of their owners," Riley said.

The majority of dams are in private, non-governmental ownership.

"The active engagement and vigilance of the dam owner, their staff, and their consulting engineers are also a critical factor in the dam safety initiative," Riley said.

Emergency preparedness is also important for dams so that if there is an emergency with a dam, the dam owner and local emergency responders know how to respond to either help prevent the failure or remove people from harm’s way if the failure is imminent.

"It is important for people who live in the area of a dam (or are considering buying property situated below a dam) to know if they are in the inundation area downstream if the dam were to fail and what they will do if they need to evacuate in the event of a dam safety emergency," Riley said.

Purchasing flood insurance for homes in the dam failure inundation area would also be wise, even though such insurance may not be mandated, according to Riley.

Riley said it is also important that individuals who are considering buying property around a man-made lake understand their potential roles and financial responsibilities associated with the lake’s dam.

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