Engineering and Mapping Solutions: Diverting Dam Disasters

While South Carolina’s historic rain event that occurred in early October 2015 brought dam safety to the attention of residents and public officials, catastrophic water management infrastructure failures have affected other areas of the country. What can be done to reduce the risk of dam breaches and collapses?

South Carolina’s 1 in 1,000-year rainfall event, which dumped more than two feet of water during five days in early October 2015, tested dams throughout the state. Unfortunately, many dams in the Midlands region of South Carolina failed, which resulted in the loss of 19 lives and millions of dollars in property damage. Just as the dramatic levee breaches that occurred in New Orleans brought the importance of regular maintenance and inspection to the forefront of public consciousness, the failure of water management infrastructure in South Carolina has started a discussion about how to prevent such disasters in the future.

The issue of dam safety is not a problem limited to South Carolina. According to the Association of State Dam Safety Officials (ASDSO), between January 2005 and June 2013, 173 dam failures and 587 safety incidents occurred in the United States. The lessons learned during the aftermath of the South Carolina dam failures have to the potential to prevent similar disasters throughout the United States.

Locating the Dams

While it is common sense that to inspect and maintain dams officials and property owners need to know the location of these structures, the reality is that many small privately owned dams are unregulated and off the radar of public officials. In fact, as of December 2015, S.C. state officials have identified 23 failed dams in rural areas surrounding the capital that were not included in the initial statewide count of 45 dam failures. Since farmers built most of these structures to protect their land, some of which have existed more than a century, maps often do not include them.

One solution to locating these dams is through the use geospatial imagery. Woolpert, Inc., a land surveying firm, took aerial photos of the areas impacted by flooding in the Columbia, S.C. region. By comparing before and after pictures, officials can identify possible locations of private rural dams. Additionally, these dams served as a vital resource during the event to prioritize their disaster responses.

Pinpointing Problems Leading to Dam Breaches and Collapses

Post collapse dam inspections provide engineers, dam owners, and public officials with vital information about the causes of the failures. For example, a team of research scientists from Georgia Tech, Clemson University, the Federal Energy Regulatory Commission, and the private sector spent four days in October 2015 surveying failed dams in the Columbia, S.C. The preliminary findings of these inspections, organized by Geotechnical Extreme Events Reconnaissance (GEER) Association and supported by the National Science Foundation, discovered many of the dam failures were preventable.

The most common causes of the dam failures identified by the GEER team in their preliminary report included:

• Poor design and construction of aged earthen dams
• Poor soil conditions constrained the performance of dams

The ASDSO recently launched a website with similar information and case studies from previous dam failures. This virtual toolbox provides engineers, property owners, and public officials with insights about the warning signs that a dam may be at risk of failing so remedial actions can be taken.

Public Education about Dam Safety

A common theme in media interviews of South Carolina homeowners affected by dam breaches is a lack of awareness of the potential risks of living downstream from water management infrastructure. In some cases, property owners were not even aware they lived near a dam. Others did not know they lived in a flood plain and needed flood insurance, which left many homeowners with uninsured flood losses.

One way commercial dam owners provide information about dam safety is to hold public information meetings. For example, Santee Cooper, a South Carolina electric cooperative, held an open meeting to inform the public about its emergency action plans in the event of a dam failure. The ASDSO hosts a website Living Near Dams, which provides essential information for dam owners and those living downstream from the structures. They also publish a brochure addressing dam safety and extreme rainfall events.

Public education about dam safety is also essential in order to secure funding for dam inspections and enforcement. When the topic of increasing the funding for dam safety programming came before the S.C legislature in November 2015, some members opposed the measure. By informing the public about the need for dam inspections, enforcement of repair orders and early warning systems, they are more likely to support their representatives in funding allocations.