OMAHA, Neb. - A blend of public laws, government regulations and government processes doesn’t likely conjure images of engineers engaged in roundtable discussions, drawing pictures on a whiteboard and bouncing creative out-of-the-box thinking strategies or groundbreaking ideas off one another.
But efforts executed by the U.S. Army Corps of Engineers, Omaha District, have proven that perhaps it should. The district achieved groundbreaking results in less than one year working levee repair projects following historic flooding.
The Missouri River Flood of 2011 ravaged communities from Fort Peck, Mont., to St. Louis, during the summer of 2011. Two critical levee systems protecting communities, agricultural land and critical infrastructure breached, allowing the Mighty Missouri River to rush through in a torrent.
The primary threats were to major interstate access, thousands of acres of agricultural land, and the town of Hamburg, Iowa. The town was in jeopardy after a critical breach on Levee L-575 while corps engineers worked with the mayor and emergency management officials to construct a temporary levee to hold back floodwaters.
Another critical breach occurred on Levee L-550 just north of Highway 136 in Atchison County, Mo. In the end, five breaches occurred on the Missouri River Federal levee system.
Prior to the end of the flood event, the previous Northwestern Division Commander Gen. John McMahon tasked the Omaha District’s Chief of Flood Risk and Floodplain Management, Randy Behm (and a team of engineers, real estate specialists, cost estimators, biologists, geographic information specialists and economists) with reviewing the floodplain system from Omaha south to Rulo, Neb., to determine whether there were constriction points. If so, he challenged the team to investigate whether levees could be set back at those points to reduce water surface elevations.
The team developed a Conceptual Levee Setback report to identify alternative floodplain management opportunities, including levee setbacks. Once the Conceptual Levee Setback report was developed, the concepts were taken to the field by the PL 84-99 manager and the Omaha Systems Restoration Team for execution in areas where levee damage was irreparable and the levees needed to be completely reconstructed. PL 84-99 is the law that supports emergency flood assistance and funding for the rehabilitation of levee systems (that are in the program) and have sustained damages a result of a flood event.
The Omaha District Systems Restoration Team was developed to carryout rehabilitation work following the flood. Early on, conceptual levee setback team members conducted analyses to come up with viable options for floodplain restoration.
Through thorough research of historic documents, the identification of trends and the incorporation of state-of-the-art computer modeling, the team identified alternative actions that could achieve a projected annual cost savings of $14 million, lower water surface elevations, reduced operation and maintenance costs and a less frequent need for emergency evacuation and cleanup costs in the future.
Additionally, the original conceptual setbacks proposed by the team aimed to achieve conservation benefits of up to 6,470 acres by reconnecting river hydrology and providing fish and wildlife with access to larger habitat areas.
Those familiar with Public Law 84-99, the law that provides strict guidelines for the management of funds associated with the repair of infrastructure following a disaster, may be scratching their heads asking “How could the team have accomplished all of this while simultaneously ensuring compliance with PL 84-99?”
1. They recognized the historic trends, potential for better results.
Behm, a 27-year corps veteran has been around long enough to learn a thing or two about flood events, their potential impact to river hydrology both in the short and long-term and ways in which other parts of the country have taken advantage of flood risk management techniques.
During the 2011 flood, McMahon was looking for ways to minimize flood impacts in the future — examples of smart floodplain management strategies and tactics. He and the team offered their insight.
The Missouri River has a well-documented history of vacillation between wet and dry period extremes, requiring savvy engineering and proactive management techniques. Upon detailed analysis of flood events, patterns from previous floods became more salient, Behm said.
With support from the commanding general, the team also revisited recommendations from the 1994 Galloway Report, a report issued by the Interagency Floodplain Management Review Committee following the 1993 Missouri River Flood. The report recommended specific policy and programmatic changes to how floodplain management should be addressed.
Among other points, it envisioned reduced flood damages, minimized upheaval and emotional impact to families and communities, provided recommendations for mitigating economic impacts, and aimed to diminish the toll on communities and taxpayers in the aftermath of flooding on the Missouri River.
The team thoroughly reviewed it as well as internal documented accounts of the floods of 1952, 1956, 1962, 1984, 1993 and 2010.
One of the first noticeable patterns they identified by the team were significant flood damages that seemed to occur in cycles along identical reaches of levees when those structures were loaded with above average discharges.
“We noticed traditional problem areas where we had experienced breaches in the past,” Behm said. “There were certain places in the river that consistently experienced high stages and high velocities due to constrictions in downstream areas of the channel.”
About 13 locations between Omaha, Neb. and Council Bluffs, Iowa and Rulo, Neb., indicated significant channel constriction below 3,000 feet of conveyance width. Constrictions in conveyance areas result in increased river stages, greater velocities and more frequent levee loading during flooding, which can lead to levee failure, overtopping or breaching.
Those constricted areas behave like a dam, backing up water and limiting channel velocity and conveyance, Behm said.
Further analysis of levee system authorization documents turned up guidelines in the Flood Control Act of 1944 which indicated that levees between Iowa and Nebraska should be constructed to withstand discharges of about 250,000 cubic feet per second at Omaha and 295,000 cubic feet per second at Nebraska City with a minimum conveyance width of 3,000 feet from levee to levee or from levee to bluff.
One way to achieve those specifications was through the consideration of repairing the levee segments in a manner that set them back farther from the river than they were originally constructed. The basic idea of a levee setback is to relocate a segment of it from its current alignment closer to the banks of the river to a location farther away from the banks. A setback alignment would take advantage of better geotechnical conditions, opening up habitat potential, and an increase in flood conveyance.
2. They worked with, educated levee sponsors about the process.
An integral aspect of achieving success with the new approach to restoring the floodplain entailed educating levee sponsors and other stakeholders about taking advantage of floodplain management tactics. In the past many of these techniques had not been seriously considered for sake of expedience, however, the extensive damage caused by 2011 flood left everyone wanting to find a better way to reduce flood risk, said John Remus, chief of the Hydrologic Engineering Branch.
Education was key, said Kim Thomas, Chief of the Omaha District Emergency Operations Center and PL 84-99 program manager. Getting sponsors to view flood events in a broader, more long-term view helped the team gain acceptance of the idea.
“It took sitting down and talking face-to-face with the sponsors and key stakeholders to explain to them what we were trying to achieve by constructing a setback levee versus repairing the previous levee in place,” said Thomas. “The levee setbacks under consideration were localized realignments of previously existing levees using a risk-based levee design.”
In the case of Levees L-575, the two major setbacks accomplished did result in the complete reconstruction of sections of those levees due to the amount of damages sustained, said Thomas.
But, careful analysis of the costs and long-term benefits associated with reconstruction were taken into account as part of the decision-making process. PL 84-99 states that levees shall be repaired to their pre-flood conditions.
In this case, due to the tremendous amount of foundation damage, the geotechnical designers’ best and only engineering solution was to relocate the levee to better foundations, thus resulting in a setback, Thomas said.
Cost estimates compared an inline repair to the cost of a setback. The estimates indicated it was cheaper to set back the levee.
Once he saw the numbers and proposals, Leo Ettleman, president of Responsible River Management and agricultural land owner behind L-575, said he quickly realized it was not only more cost-prohibitive to repair the levees in place than to set them back, it was the only ostensible engineering solution considering the amount of damage sustained.
Working through the PL 84-99 process with the corps was a learning experience for everyone involved, Ettleman added.
“All of these were massive projects that none of us had ever been through,” he said. “This was a 500-year event and a tremendous amount of damage to personal and business property occurred. Watching everybody keep their emotions in check and get through the process was certainly encouraging.”
“The levee sponsors really made this a priority,” said Thomas. “They were obligated to take on quite a load to make these repairs in a timely manner. That meant relocating utilities, county roads and other major tasks. They worked diligently to get the work done.”
3. They capitalized on the economic savings.
The old saying, “Show me the money” rang true once the team began its development of the Project Information Report, the document that is required of all PL 84-99 rehabilitation activities.
It served as the basis for justifying the construction of setback levees to the corps headquarters for approval. In multiple instances, side-by-side comparisons of cost estimates juxtaposing the cost of in-place repairs with setback alternatives indicated cost-benefit ratios that consistently favored setback alternatives.
These highly damaged reaches typically had deep scour holes near the levee toe and extensive seepage areas. “In some cases, setting the levees back from the scour and seepage areas was the best engineering solution,” said Bryan Flere, levee safety program manager.
The levee sponsors, along with corps technical experts, leveraged relationships with the corps’ Missouri River Recovery Program, counties, levee stakeholders, State of Iowa Department of Natural Resources and the Natural Resources Conservation Service to cut the cost of borrow construction materials including sand deposits and dirt from conservation land owned by the Corps of Engineers and managed in partnership with the state and NRCS to construct the setback levee units.
“The major savings in using the corps’ recovery lands as a borrow source was that in most cases the transportation distances were much shorter to the construction sites. In total, more than 3 million cubic yards were used with savings of an estimated $2 per yard,” said Brad Thompson.
4. They used technology to their advantage.
The team made use of state-of-the-art industry standard river engineering software HEC-RAS, which stands for Hydrologic Engineering Center-River Analysis System.
When the corps was in the process of developing its National Levee Database, the Omaha District Levee Safety Program conducted an inventory and analysis of the district’s current levee system, gathering critical data about the original construction design of levees, historical maintenance information and the status of levee conditions.
In 2009, the Flood Risk and Floodplain Management Section also completed a floodway model for FEMA to support the agency’s update of their floodplain mapping information.
The team input information from both data sets into HEC-RAS and included Geospatial Information System overlays to analyze potential areas of concern along the river, said Behm.
Tony Krause, hydraulic engineer, said the combination of data sets and GIS information in the system made it easy to identify historic damage points and locations where levees appeared to be located too close to the river.
5. They remembered to be good environmental stewards.
Secondary benefits of the setback levees were the additional acres of land that were reconnected to the historic floodplain and wetlands created through borrow activities.
The corps has been working to mitigate habitats lost due to the development of the Bank Stabilization and Navigation Project, which was constructed from the 1940s through the 1970s and resulted in negative impacts to the ecosystem.
The conceptual setback levee projects identified 6,470 acres of land that could potentially be reconnected to the river. Actual on-the-ground repairs resulted in approximately 2,000 acres of reconnected flood plain and created an anticipated 500 acres of wetlands associated with borrow activities — land that will help influence shallow water habitat benefits for the threatened and endangered pallid sturgeon and other fish and wildlife. A focus on fish and wildlife is one of the corps’ eight congressionally authorized purposes for regulating operations within the Missouri River basin.
”It was good working with the [corps] because they were willing to incorporate innovative ideas that were going to benefit wildlife at the same time as improving the levee projects along the river,” said Carl Priebe, wildlife biologist with the Iowa Department of Natural Resources.
Iowa DNR manages corps property that has been acquired for mitigation for the Missouri River Recovery Program.
Priebe said he looks forward to lower river stages and more fish and wildlife habitat during future flood events.
“Before there were just grass and trees in many of these places,” said Priebe. As the river interacts with this newly connected land and wetlands, Priebe said he expects to see more diversification of various species of fish, mammals and birds taking advantage of the new landscape.
“It’s public access land so anyone can come enjoy it and its going to be land that has a wealth of opportunity for outdoor pursuits whether it be hiking, bird-watching, hunting or photography. There are opportunities for all of those things now on that public land where there haven’t been before.”
Two large-scale levee setbacks, several miles each, were completed as a result of the team’s efforts. Several smaller scale setback projects were also constructed. Total levee rehabilitation work totaled $160 million. Critical repair work was completed prior to the start of the 2012 runoff season, which began March 1, 2012. The majority of the remainder of repair work was completed in the fall of 2012 with a few final projects set for completion this spring.
“Our contractor, construction personnel and engineers executed this work in record time with no accidents and that’s commendable,” said Thomas. “All of our think tank construction and engineering folks were also right there providing great quality assurance and engineering oversight that helped move this rehab work along as efficiently as possible, within budget and ahead of schedule.”
Other communities that have faced flooding issues in the past have also paid attention to the team’s work. The State of California recently requested a copy of the final Conceptual Levee report.
The Conceptual Levee Setback team was recognized in 2012 as the Northwestern Division Innovative Project Delivery Team of the Year. Additionally, Behm received a national award, Flood Risk Manager of the Year.
The Omaha District Systems Restoration team won the corps' Outstanding Unit/Team Award for Specialized Services and Construction Contracting.
|Date Posted:||02.08.2013 17:33|
|Location:||OMAHA, NE, US|
This work, Sustainable solutions: How the Corps of Engineers used creativity to maximize flood risk reduction, by Monique Farmer, identified by DVIDS, is free of known copyright restrictions under U.S. copyright law.