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  4. Southwestern Illinois Levee Project

Just outside of St. Louis, in Southwestern Illinois, a crisis was unfolding. On August 15, 2007, the Federal Emergency Management Agency (FEMA) announced its intent to “deaccredit” the Mississippi River levee systems protecting The American Bottoms. This decision carried dire economic and financial consequences for businesses and residents alike. “It was going to affect how buildings were built, how much insurance the residents and businesses were going to pay,” recalled Charles (Chuck) Etwert, Chief Supervisor of Construction and the Works for the Southwestern Illinois Flood Prevention District Council. “It was a big deal.” 

In reality, it was more than just a big deal—it was a potential catastrophe. The levees safeguard The American Bottoms, a 174-square-mile region of immense economic and historical significance. Home to over 156,000 residents and more than 4,000 businesses employing 56,000 people, the area also houses major manufacturing facilities of national importance. Its extensive multimodal transportation infrastructure positions it as a critical hub for future commerce and industry. In addition, the area includes the Cahokia Mounds, a UNESCO World Heritage Site representing the largest and most complex pre-Columbian Native American city north of Mexico, serving as a vital cultural and spiritual center for the Mississippian people. 

The repercussions of deaccreditation would be swift and severe: flood insurance premiums would skyrocket—over $20 million for individuals and small businesses and another $30 million for larger corporations. Property values would plummet, and new prohibitively costly building regulations would take effect. More critically, without accredited levees, the risk of catastrophic flooding loomed large. Potential damage estimates ranged in the tens of billions, threatening the stability and prosperity of the entire region. Action was not just necessary, it was urgent. 

YEARS AHEAD OF SCHEDULE
20+
IN SAVINGS
$10M+
REGION PROTECTED
174mi² 

Location

  • Illinois, USA
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Protecting a legacy: Holding back the mighty Mississippi

The first levees in the American Bottoms were built in the late 19th and early 20th centuries by local landowners and drainage districts to protect farmland and small settlements from seasonal flooding. These early structures were rudimentary and often failed during major flood events. The devastating Great Flood of 1927 underscored the need for stronger flood protection, prompting the federal government through the Flood Control Act of 1928 (and subsequent flood control acts) to authorize the U.S. Army Corps of Engineers (USACE) to construct and improve levee systems across the Mississippi River basin.

This effort resulted in a 65-mile levee system protecting the St. Louis Metro East region, consisting of five distinct levee systems spanning Madison, St. Clair, and Monroe counties in Southwestern Illinois. These levees successfully held back the Great Flood of 1993, proving their resilience but also highlighting the necessity for ongoing assessment and upgrades.

That ongoing assessment process led in part to the crisis in 2007. After reviewing the system, USACE reported "reduced confidence" in the levees’ ability to protect against a 100-year flood event. Based on these findings, FEMA announced that the levees no longer met federal accreditation standards, effectively reclassifying much of St. Louis' Metro East as an unprotected floodplain.

The issue was not due to neglect or a sudden deterioration of the levees but rather a shift in engineering standards and risk assessment methods. In order to meet FEMA’s accreditation requirements, USACE recommended an extensive levee system upgrade and replacement—an immense and costly endeavor projected to take decades and require an investment of hundreds of millions of dollars. The region faced a stark choice: act swiftly to restore confidence in its current flood protection system or risk significant economic and infrastructural damage.
 

Bridging the gap: Expertise, innovation, and trust

Recognizing the urgency of the situation, the State of Illinois and the three affected counties moved swiftly, establishing the Southwestern Illinois Flood Prevention District (FPD) Council in July 2009 to secure funding and manage the levee system’s repair and reconstruction. New legislation provided capital, but engineering expertise was essential to identify and resolve deficiencies while ensuring the levees met FEMA’s rigorous flood protection standards—on an accelerated timeline.

Restoring confidence in the levee system was no small task. It required specialized, multidisciplinary expertise to navigate complex engineering, regulatory, and logistical challenges, along with a deep understanding of FEMA and USACE regulations. Ultimately, we were awarded the project, but securing the contract was far from straightforward. 

“The process of being awarded this project was multifaceted.” says Jon Omvig, Senior Vice President of WSP in the USA and Project Manager for the Southwestern Illinois levees project. “Initially we were hired (by the FPD Council) to evaluate the cost estimate developed by USACE. While the Council appreciated the work we had completed and had confidence in our preliminary analysis, they recognized that a project of this magnitude would require a competitive selection process.” What followed was a Design Competition wherein three engineering firms were invited to prepare a brief plan, schedule, and cost estimate for restoring FEMA accreditation. 

After assessing the USACE cost estimate and before the design competition, we conducted a thorough levee screening against FEMA accreditation criteria. During the competition, our team prioritized maximizing the use of existing levee infrastructure to deliver both cost efficiency and the level of flood protection required by FEMA—within a reasonable budget. We also proposed an accelerated schedule that allowed construction to begin before land acquisition was complete, a calculated risk aimed at securing FEMA accreditation before the levees could be reclassified. Once selected to design the improvements, our work was directly informed by the deficiencies identified during the screening. These insights proved critical in determining the necessary fixes to meet FEMA standards.

These factors were critical in gaining the Council’s trust, but our team’s success went beyond engineering capabilities. “We had the technical expertise,” explains Omvig. “But the key to us winning this project was we understood the nuances between FEMA and the USACE and were able to bridge the gap between their similar but distinctively different regulations.” 

How levees work and the challenge of seepage

Levees are engineered embankments designed to protect low-lying areas from flooding by acting as barriers that contain rising water levels. They are typically constructed from compacted soil, clay, or engineered materials and are reinforced with drainage structures, such as relief wells and seepage berms, to manage water pressure and prevent failure.

One of the greatest challenges levees face is seepage, which occurs when water infiltrates the levee system, potentially weakening its integrity. Seepage can manifest in two critical ways:

  • Through-seepage happens when water moves horizontally through the levee, eroding material and potentially causing internal instability.
  • Underseepage occurs when water flows beneath the levee through permeable soil layers, creating pressure that can lead to sand boils—a sign of potential levee failure.

If left unaddressed, excessive seepage can compromise levee stability, leading to erosion, structural weakening, or even catastrophic breaches. Effective flood protection requires careful engineering solutions, such as relief wells, seepage berms, and cutoff walls, to control water movement and maintain levee integrity.

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Strengthening success: Our role in enhancing southwestern Illinois levees

We played a critical role in the Southwestern Illinois Levees project by providing a range of specialized engineering and construction management services to enhance flood resilience and secure FEMA accreditation. Our contributions included:

Geotechnical and structural assessments

We conducted extensive subsurface investigations, including soil borings and geotechnical testing, to evaluate foundation stability and seepage risks. This data informed critical decisions about underseepage mitigation, relief well placement, and the design of seepage berms. Structural assessments of levee components, such as floodwalls, culverts, and closure structures, ensured they met modern safety standards.

Seepage and stability improvements

A major focus of our work was addressing underseepage and through-seepage risks. The team designed and optimized relief wells to improve drainage efficiency while minimizing new construction costs. They also implemented hybrid seepage solutions, integrating existing relief wells with strategically placed seepage berms to enhance performance while reducing material and excavation costs.

Hydraulic and hydrologic modeling

We performed detailed hydraulic and hydrologic studies to assess floodplain impacts, internal drainage conditions, and rainfall severity. This included modeling how water would move through the levee system under extreme flood conditions and optimizing pump station capacity and drainage structures to handle prolonged flood events.

Value engineering and cost optimization

To ensure project affordability without compromising safety, we applied advanced 3D modeling techniques to refine construction plans, minimizing unnecessary excavation and material use. By leveraging existing infrastructure wherever possible, we helped the FPD Council significantly reduce project costs while still achieving the necessary improvements.

Construction support and quality assurance

We also provided oversight and technical support throughout construction, ensuring work adhered to FEMA and USACE standards. We assisted with contractor coordination, material testing, and compliance verification to ensure that every upgrade met rigorous flood protection requirements.

In-depth analysis: 4 ways we delivered technical excellence in levee engineering

The Southwestern Illinois levees project was extensive and complex, with our team offering a broad array of services. However, four key aspects showcase our technical excellence and innovative solutions. We invite you to explore these in greater detail and discover how our advanced services made a significant impact.

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Advanced investigations and analysis

Uncover how we leveraged cutting-edge technology to enhance characterization, enabling a more precise and effective design approach.

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Utilization of existing relief wells (RW)

Dive beneath the surface to see how we innovatively repurposed existing wood stave relief wells, meeting modern performance standards.

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Pump stations evaluation

Explore how our teams optimized existing pump station infrastructure, eliminating the need for new construction while improving efficiency.

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Construction highlights

E. St. Louis Sewer Optimization, America’s largest cutoff wall. Discover two groundbreaking construction projects where we pushed engineering limits, delivering substantial time and cost savings.

Certified, secured, and decades ahead of schedule

The rehabilitation work on the Southwestern Illinois levee systems was completed in February 2018, paving the way for their eventual certification by FEMA. Our strategic approach—prioritizing cost efficiency and leveraging existing infrastructure—enabled the Southwestern Illinois Flood Prevention District to secure accreditation ahead of schedule and under budget.

Through extensive characterization of existing structures and subsurface conditions, our teams provided detailed assessments that informed targeted improvements. By integrating design optimization and value engineering, the project delivered tailored solutions for each levee segment, ensuring resilience without unnecessary costs. The result: a fully accredited levee system at a total construction cost of approximately $75 million—far below early estimates in the hundreds of millions. Even more impressively, the project was completed decades ahead of initial projections. This achievement not only safeguarded critical infrastructure but also restored confidence in the region’s flood defenses.

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The ultimate test: The flood of 2019

On June 8, 2019, the Mississippi River at St. Louis surged to 45.93 feet—effectively reaching 100-year flood levels. Compounding the challenge, the flood’s duration was the longest ever recorded. This historic event occurred just after the completion of the levee improvements which had been specifically designed to withstand such a flood.

“I was out there during the 2019 flood,” recalled Mary Knopf, Lead Geotechnical Engineer. “It's the mighty Mississippi, as people like to say, and it almost looked like the ocean. Then I walked down to the bottom of the levee where the only thing between you and that ocean is the levee. That's a pretty scary position to be in. The water wants to move the levee. And I was going through our cross sections in my mind, and I was thankful for every conservative choice we made.”

Knopf was right. Despite the extreme conditions, the Southwestern Illinois levee systems held strong, performing exactly as intended. Our team and local stakeholders not only successfully reinforced the region’s flood defenses, but did so well ahead of previously estimated project timelines, ensuring critical protections were in place when they were needed most. Through strategic planning and engineering expertise, our team delivered critical, time-sensitive protection to the communities and businesses of the American Bottom, preventing what could have been a catastrophic outcome.

“You never know after a project is built—how’s it going to perform?” reflects Chuck Etwert on the levee improvements. “But everything performed just exactly as we thought it would.” 

A potential disaster was transformed into a resounding success, safeguarding the region for years to come.

Impacts on the community

  1. Economic and financial stability: The project prevented a potential catastrophe that would have had dire economic and financial consequences for businesses and residents. By securing FEMA accreditation for the levee systems, the project avoided skyrocketing flood insurance premiums, plummeting property values, and costly new building regulations.
  2. Protection of critical infrastructure: The levees safeguard a 174-square-mile region of immense economic and historical significance, including major manufacturing facilities, extensive multimodal transportation infrastructure, and the Cahokia Mounds, a UNESCO World Heritage Site. The successful rehabilitation of the levees ensured the protection of these critical assets.
  3. Community safety: The project addressed the risk of catastrophic flooding, which could have caused damage estimates in the tens of billions and threatened the stability and prosperity of the entire region. By enhancing flood resilience, the project provided essential protection to the community.
  4. Cost efficiency and timeliness: The project was completed ahead of schedule and under budget, with a total construction cost of approximately $75 million—far below early estimates in the hundreds of millions. This achievement not only safeguarded critical infrastructure but also restored confidence in the region’s flood defenses.
  5. Successful performance during flood events: The levee improvements were put to the test during the historic flood of 2019, and they performed exactly as intended, preventing what could have been a catastrophic outcome. This demonstrated the effectiveness of the project in providing critical, time-sensitive protection to the community. 
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Meet the Visioneers

Our team of Visioneers played a pivotal role in the success of the Southwestern Illinois Levees project. With a diverse and multidisciplinary team, we brought together expertise from various fields to deliver innovative solutions and ensure the resilience of the levee systems. Here are some of the key Visioneers who contributed to this remarkable achievement:

  • Jon Omvig: Senior Vice President of WSP in the USA and Project Manager for the Southwestern Illinois levees project. Jon's leadership and deep understanding of FEMA and USACE regulations were crucial in bridging the gap between their distinct standards.
  • Jo Tucker: Principal and Senior Technical Advisor. Jo's expertise in value engineering and design optimization helped refine construction plans and reduce project costs while maintaining safety.
  • Mary Knopf: Lead Geotechnical Engineer. Mary's thorough geotechnical assessments and conservative choices ensured the levee systems' stability during the historic flood of 2019.
  • Randy Cook Jr.: Deputy Project Manager and Civil Design Lead. Randy's breadth of knowledge about the stakeholders and various technical disciplines helped deliver a successful project.  

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