Levees, man-made embankments or concrete floodwalls designed to divert temporary floodwaters, are integral to many communities across the United States. “People may think we manage all levees, but that’s not the case,” said Tammy Conforti, Levee Safety Program manager with the U.S. Army Corps of Engineers (USACE). Even though 14,500 miles of levees (or just 10 percent of the nation’s levees as estimated by the National Committee on Levee Safety) are in its Levee Safety Program, USACE continues to aggressively advance new methodologies for assessing, communicating, and managing inundation risks associated with levees.
With more than 10 million people living or working behind levees within its authority, USACE considers the role it has in assessing and communicating risks a top priority. “We have a common vision for dam and levee safety. That vision is to approach infrastructure from the perspective of people living and working behind it,” said Eric Halpin, USACE special assistant for dam and levee safety. The goal is to better manage risk, which he described as a “shared responsibility” involving not only USACE but also other federal, state, and local agencies, plus the general public. “We deliver flood risk benefits commensurate with risk that exists, but with the principle that life safety is paramount.”
It Starts with Information
Levee inventory information serves as the foundational element of the USACE Levee Safety Program, because the information collected allows for implementation of other activities, including screening levees to characterize the benefits and risk they pose; conducting initial risk assessments to answer key questions regarding priorities, urgency of action, and type of action; and coordinating and communicating Levee Safety Program efforts with stakeholders and other agencies to build the foundation for shared responsibility to develop risk reduction measures.
In the past five years, USACE has spent a significant amount of effort inventorying levees within its authorities and now has moved on to collect available information from other levees outside of its authorities for inclusion into the National Levee Database (NLD).
The NLD includes a geo-reference database system that allows users to visualize the levee’s location and graphically overlay current weather information. Other screens can overlay flooding risks based on past storm history. During torrential rains in 2011, for example, this function allowed USACE as well as state and local agencies to identify locations where levees on the Lower Mississippi River were most vulnerable to overtopping. Such information was important in guiding emergency preparedness and promoting situational awareness for federal, state, and local officials and the general public.
Missouri River levee L550 breached on June 23, 2011, near Watson, Mo. Over the following months, USACE focused its energy and resources on repairs and temporary fixes that could be completed in a tight time frame and placed 2.7 million cubic yards of material in 86 days. That’s an average of 31,000 cubic yards of material a day. With those critical repairs completed, efforts have turned to geotechnical investigations and execution on permanent solutions to restore the level of flood risk reduction in the basin. USACE Omaha District photo by Eileen Williamson
NLD’s interoperability also was a major plus in identifying potential hazards from Hurricane Isaac in 2012. The system was able to show Isaac’s projected storm track over the NLD’s maps to identify levees, population centers, and other critical infrastructure that were at risk from the storm.
Documenting all the levees nationwide is its own Herculean task. The Federal Emergency Management Agency (FEMA) alone has identified more than 29,000 miles of levees nationwide as part of the National Flood Insurance Program. Approximately 8,000 miles of those levees are also USACE program levees. One of USACE’s current priorities is to work with other organizations such as FEMA to incorporate their levee information into the NLD.
The NLD site has been open to the public since October 2011 and can be viewed at nld.usace.army.mil. So far, the site has registered millions of hits, while agencies such as FEMA and the National Oceanic and Atmospheric Administration directly connect to the database as part of their essential missions. “Other agencies use this data in preparing for natural disasters,” Conforti said.
The Risk Context
USACE is on the road to a cultural shift in how it assesses and talks about levees. In conjunction with collecting data about the physical features of levees, it is also important to know how they are expected to perform and what the potential consequences are in cases of poor performance. The essential questions are: What is the range of possible loading events (flood, storm, or earthquake, etc.)? How will the levee perform when subjected to these events? What are the consequences if the levee doesn’t perform well – losing lives is of paramount concern. More simply: What is the likelihood and severity of undesirable or adverse consequences? In this environment, “one of our major priorities is risk communication,” Conforti said.