Background

As climate change exacerbates the intensity and frequency of extreme weather events, floodplain managers are rethinking their relationship with levee systems. One concept being explored around the country is floodway expansion with levee setback realignment, which involves moving a levee away from a river and reconnecting a greater portion of its historic floodplain. Water resource managers can achieve multiple benefits with this combination of natural and gray infrastructure: they can maintain or even increase the level of flood risk reduction, enhance habitat for fish and wildlife, create new recreational opportunities, and promote more equitable future floodplain land use practices.

Levees have been a central feature of flood risk management along rivers for many decades. When properly designed, constructed, and maintained, they can provide substantial benefits for flood risk reduction to nearby communities. Many of our nation’s levees were constructed in the mid-twentieth century, when the main goal was to allow communities to maximize their economic development on the land alongside the levee. As a result, levees were constructed close to the banks of rivers and streams, cutting off the river from the surrounding floodplain. 

While this approach had the intended economic development impacts, the decision to separate rivers from their historic floodplains with artificial engineered structures was detrimental to riparian ecosystems and the ecosystem services – dynamic and responsive flood water attenuation, valuable water filtration and absorption, and habitat, among others – that they provide. In California’s Central Valley, for example, some species of salmonids have critical developmental stages that depend on annual floods that once created vast expanses of shallow water habitat in riparian floodplains.

For some communities the protection afforded by levees spurred floodplain developments and created economic growth. However, levees were built without an understanding of the now popularized “levee effect”, which recognizes that while levees provide protection from hazard, they inadvertently exacerbate risk by inspiring development in harm’s way. There is no levee that can protect against all flood conditions and with changing climatic conditions, the protections provided by our existing levee infrastructure are becoming less certain. 

Levee Setbacks: An Opportunity for Engineering With Nature

The US Army Corps of Engineers spends hundreds of millions of dollars every year to repair, rehabilitate, and restore levees that are damaged by floods. Much of that money flows through the Rehabilitation and Inspection Program (RIP), a program governed by Public Law 84-99. The program was created by Congress in 1941 to ensure that communities affected by floods are able to restore flood protections quickly. However, over the years policymakers in Congress and communities across the country have seen the potential to do more with PL 84-99 than simply rebuild a levee system that has failed once and is likely to fail again. 

Levee System L-536 in northwestern Missouri is a great example of a levee setback. In 2019, abnormal weather patterns in the Midwest led to record-setting flooding along the Missouri River and caused widespread, catastrophic damages throughout the Missouri River Valley. L-536 experienced five full and two partial breaches, as well as significant erosion along the top and sides of the levee. The resulting devastation in Atchison County, Missouri, included flooding of more than 160 homes, nearly 1,300 agricultural buildings, and 14 commercial businesses, destruction of 121 miles of roads, major disruption to the BNSF Railroad, a 216-day closure of US Highway 136, and submersion of 56,000 acres by floodwaters.

Prolonged high-water conditions prevented the Corps from immediately conducting a damage assessment and repairs, but provided an inadvertent benefit: time. With this time, the local levee district consulted with the Corps’ Omaha District and affected property owners about the possibility of a levee setback. Ultimately, the assessment determined that the most cost-effective and technically feasible alternative was to construct a partial levee setback, in addition to some in-line repairs. In total, a 25,400-foot section of L-536 was built farther away from the river, encompassing a large section of the historical floodplain. The L-536 setback has created greater flood resilience for the levee system and reduced risks to landward buildings and cropland. It is expected to reduce operation and maintenance costs and reduce the flood risk to nearby communities, transportation networks, and infrastructure. It has also reconnected more than 1000 acres of floodplain and established 400 acres of new, high-value wetland habitat for fish and wildlife.

Late last year, the Corps published a proposal to revise its regulations governing implementation of PL 84-99. We saw this as a prime opportunity to push for policy changes that will enhance the Corps’ analysis and implementation of levee setbacks. Our comments are detailed but boil down to one simple concept: Levee setbacks are an effective way to achieve the multiple objectives of flood risk reduction, environmental sustainability, and other social benefits that define the Corps’ modern mission.

You can read our comments on the draft rules here.

Team

Matthew Shudtz, Law and Policy Fellow, UGA Institute for Resilient Infrastructure Systems

Matthew Chambers, PhD Student, Research Professional III, UGA College of Engineering

Yee Huang, Law and Policy Analyst, UGA Institute for Resilient Infrastructure Systems

Partners

Our team is grateful for the insights and advice provided by Viv Bennett and Jimmy Hague from The Nature Conservancy, David Crane from the Corps’ Omaha District office, and Rod Lammers from Central Michigan University.