AMERICAN SOCIETY OF CIVIL ENGINEERS
The nation’s estimated 100,000 miles of levees can be found in all 50 states and the District of Columbia. Many of these levees were originally used to protect farmland, and now are increasingly protecting developed communities. The reliability of these levees is unknown in many cases, and the country has yet to establish a National Levee Safety Program. Public safety remains at risk from these aging structures, and the cost to repair or rehabilitate these levees is roughly estimated to be $100 billion by the National Committee on Levee Safety. However, the return on investment is clear – as levees helped in the prevention of more than $141 billion in flood damages in 2011.
Levees: Conditions & Capacity
Levees play a critical role in reducing the risk to public safety from potentially devastating flood events throughout the United States. Levees are man-made structures designed and constructed along the water’s edge to contain, control, or divert the flow of water in a flood event. In the mid to late 19th century, many of our nation’s levees were originally designed and built to protect farmland. However, with continued development in our nation’s floodplains, these levees are now protecting major urban and residential areas. Due to increased concerns regarding the resilience of our national levee systems, in 2007 Congress directed agencies to gather data on the condition of our nation’s levees, thereby creating the National Levee Inventory. However, Congress has yet to pass legislation creating a National Levee Safety Program.
According to the Federal Emergency Management Agency (FEMA)’s Midterm Levee Inventory (MLI), levees are found in approximately 30% of the nation’s 3,068 counties, with 43% of the nation’s overall population living in a county with at least one levee. While the true extent of the nation’s entire levee system is still unknown, it is estimated that as many as 100,000 miles or more of levees exist, with tens of millions of people living or working in these levee- protected areas. Currently, 35,682 miles of levees can be found in FEMA’s levee inventory; however, the full condition of each of these levees is not yet determined. As nearly 85% of the nation’s estimated levees are locally owned, operated, and maintained, it is difficult to collect information from such disparate local entities.
The National Levee Database (NLD), operated by the U.S. Army Corps of Engineers (USACE), is an inventory of most of the levees that the USACE has designed, maintained, and inspected, and is available to the public. The NLD inventory currently comprises approximately 14,700 miles of levees, or about 2,350 systems. The FEMA levee inventory will eventually be combined with this national inventory to provide a single comprehensive source for users to identify areas of concern and to access information about levees in their neighborhood. The goal is to obtain additional data from states and local authorities to include almost all levees in the country.
The levees in the NLD average more than 55 years old and protect approximately 14 million people who live or work behind the structures. In 2011, these levees helped in the prevention of more than $141 billion in flood damages, and they provide a 6:1 return on flood damages prevented compared to initial construction costs. Larger levee systems such as the Mississippi River and Tributaries system can provide as much as a 24:1 return ratio. Unfortunately, of the USACE monitored levees that have been rated, only 8% are found to be in acceptable condition, while about 69% are minimally acceptable, and 22% are labeled as unacceptable.
During the past 50 years there has been significant development on lands protected by levees. Combining tremendous development and rising sea levels with minimal federal, state, and local resources to repair and maintain these levees is placing people and infrastructure protected by levees at risk in a flood. The lack of formal federal, state, and local government oversight, sufficient technical standards, and effective communication of the risks of living behind a levee is placing people and property in danger of flooding.
Both the USACE and FEMA have invested in coordinated efforts to increase awareness and outreach to people living and working around levees. These agencies are now working collaboratively to share information and data, synchronize work efforts, and align program requirements while actively involving local, state, and other federal agencies. For example, FEMA and the USACE participate in a task force to address concerns related to levees and to better align National Flood Insurance Program (NFIP) levee accreditation requirements with levee inspections performed by USACE. FEMA and the USACE are also partnering to develop joint messaging and publications to explain their respective roles in addressing levees and to help communities better understand their own levee-related roles and responsibilities.
FEMA is currently working not only to map the nation’s levees, but to increase awareness of potential hazards and mitigate those hazards. The program is designed to deliver quality data to increase public awareness, by building on already existing flood hazard data and maps that were produced during the Flood Map Modernization program. Ideally, those areas that are most in need of updated maps will be provided that information as efficiently and expeditiously as possible.
About the American Society of Civil Engineers (ASCE)
“Founded in 1852, the American Society of Civil Engineers (ASCE) represents more than 147,000 members of the civil engineering profession worldwide, and is America’s oldest national engineering society. ASCE’s vision is to position engineers as global leaders building a better quality of life…Comprised of Regional Councils, Younger Member Councils, Sections, Branches, Student Chapters and Clubs and International Student Groups, the Society and its volunteers are fully engaged in making this a better world by design.”