Protecting New Orleans: From Hurricane Barriers to Floodwalls
Released: 2006-01-26T00:00:00

Introduction

New Orleans' location on the Gulf Coast with water on three sides and below-sea-level terrain makes this densely populated section of Louisiana highly susceptible to flooding from hurricane storm surges. New Orleans' flooding threats are not only from the coast but also from the Mississippi River and rainfall that gets trapped in the city, known as stormwater . The system of levees and floodwalls around the city is designed to provide a specified level of protection from riverine and coastal flooding; where as, massive pumps and drainage canals that flow into Lake Pontchartrain manage the city's stormwater. Local levee districts maintain the hurricane levees and floodwalls that were built largely by the U.S. Army Corps of Engineers as part of its Lake Pontchartrain and Vicinity Hurricane Protection Project to protect New Orleans and the surrounding parishes from a Category 3 hurricane. The Sewerage and Water Board of New Orleans is responsible for the city's stormwater management infrastructure.

Breaches of the floodwalls protecting New Orleans during Hurricane Katrina were the major contributor to significant flooding in many areas of downtown. Although most of the levee breaches in coastal Louisiana were the result of the storm's surge flowing over levees, preliminary evidence suggests that three major breaches in downtown New Orleans occurred prior to the floodwalls being overtopped; that is, the floodwalls failed before their design was exceeded. The failure of these floodwalls to reliably perform has many stakeholders' speculating about the causes of the failures.

A question central to many of the investigations into Katrina-related damage and of concern in rebuilding efforts is: were the levees and floodwalls breached because their design was exceeded, or did they fail due to faulty design, construction, or maintenance? To answer these questions, evidence has and continues to be collected on numerous fronts, including evidence of the height of the storm surge in various locations, and how the levees and floodwalls performed. Technical experts from universities, professional engineering organizations, and the Corps are using this evidence to model and explain the performance of New Orleans' hurricane protection system. The findings are likely to shape not only the future design of the hurricane protection system but also plans for rebuilding sections of the city and perspectives on the federal role and responsibility in the city's rebuilding efforts. Moreover, the findings may improve understanding and change perceptions of the level of flood protection and risk in other U.S. cities.

Understanding why New Orleans' hurricane protection system failed is essential for moving beyond simply making repairs to damaged levees and floodwalls. Knowing why the floodwalls failed is central to assessing the city's vulnerability to storm surge flooding and deciding on how to most effectively combine approaches for managing flood risk during rebuilding efforts (e.g., investing in coastal wetlands loss and hurricane protection infrastructure, requiring flood-proofing in certain areas, and mapping areas for the federal flood insurance program). Nonetheless in order to be prepared for the 2006 hurricane season, the Corps is having to proceed with immediate repairs of damaged levees and floodwalls using available information and integrating new information as it is available.

One of the causes of failure being discussed is a poor or inadequate design for protecting the city from a Category 3 hurricane. The original project design was to control storm surge flowing into water bodies near downtown by building inlet barriers and canal floodgates. During the project's construction which began with authorization in 1965 and was ongoing when Hurricane Katrina made landfall, numerous factors contributed to changing the design of how to protect the city (e.g., including local environmental concerns, changing cost estimates, local flood protection preferences, and litigation); the final design attempted to reduce hurricane-related flooding in the city by increasing the height of levees and floodwalls, in lieu of the barriers and floodgates.

The Corps' decision in the mid-1980s to recommend higher levees instead of the inlet barriers it had recommended in 1965 was shaped by multiple factors, including environmental litigation, project economics, and local preferences. The Corps preferred floodgates to floodwalls along the Orleans Avenue and London Avenue canals. The decision to not build floodgates, and instead build floodwalls along the canals, was made by the local project sponsors. The original design and the final design were intended to provide the same level of protection, i.e., protection from the rough equivalent of a Category 3 storm surge.

This report discusses the evolution in the project's design, with specific reference to how and by whom design decisions were made. The focus is on two major design developments relevant to the current investigations into the floodwall failures in downtown New Orleans' during Hurricane Katrina: (1) the shift from the barriers at the inlets to Lake Pontchartrain to higher levees along the lake; and (2) the shift from floodgates at the mouth of the city's stormwater outfall canals that drain into Lake Pontchartrain to higher floodwalls along the length of the canals. The report includes an appendix summarizing the federal funding history for the Lake Pontchartrain project. The analysis contained herein is based on currently available information and is limited in scope.

New Orleans Hurricane Protection

Hurricane Katrina's Floodwall Breaches: A Primer

Although there were more than a dozen breaches and many other segments of damaged levees and floodwalls in the greater New Orleans area and numerous in other coastal Louisiana parishes, the four breaches (see Figure 1 ) of the Lake Pontchartrain project that have received the greatest attention due to their impact on downtown New Orleans were the following:

a breach of the 17 th Street Canal floodwall; two breaches of the London Avenue Canal floodwall; and a breach of the western flank of the Inner Harbor Navigation Canal (IHNC, also known as the Industrial Canal) floodwall.

Flooding due to overtopping of city's levees and floodwalls was predicted for storm surges from a storm stronger than a Category 3 hurricane passing close to the New Orleans region. Extensive overtopping may cause a levee or floodwall breach. Breaching in urban areas often produces catastrophic damage. Hurricane Katrina had weakened from a Category 5 storm to a Category 4 storm by the time passed east of New Orleans. Overtopping was the cause of much of the flooding and most of the breaches and damage to the hurricane protection infrastructure in coastal Louisiana. However, overtopping does not appear to have caused much of the flooding and some of the breaches in downtown New Orleans.

A November 2005 preliminary analysis of the performance of New Orleans' hurricane protection system by technical expert teams from the University of California at Berkeley and the American Society of Civil Engineers indicate the method of failures at the breaches in downtown New Orleans. The teams' preliminary evidence suggests that breaches along the 17 th Street and London Avenue canals occurred before the floodwalls were overtopped; that is, these floodwalls failed before their design was exceeded. The immediate and underlying causes of these breaches (i.e., what led to the failures) are the subject of conjecture; hypotheses range from exceeded design, poor design, faulty construction, maintenance issues, incomplete construction due to the level of construction appropriations (see the Appendix for information on the project's federal funding), and modifications to the project's original design. The Corps has initiated a forensic investigation of the floodwall breaches; the results are expected in June 2006. According to the teams' preliminary analysis, the combined storm surges from several direction along the IHNC and the Mississippi River Gulf Outlet (MRGO) overtopped the IHNC and MRGO.

Lake Pontchartrain Project

Congress authorized the Corps to protect New Orleans from the rough equivalent of a Category 3 storm when it authorized the Lake Pontchartrain and Vicinity Hurricane Protection Project in October1965. The project consists of levees and floodwalls, most of which were constructed by the Corps and cost-shared by the federal government and local levee districts. The Orleans Parish segments of the Lake Pontchartrain project, which encompass downtown New Orleans, were 90% complete as of May 2005. The total cost for the Lake Pontchartrain and Vicinity project is $738 million, with the federal responsibility $528 million. Federal allocations totaled $457 million through FY2005, leaving around $70 million to complete federal funding.

The original design of the Lake Pontchartrain project was sent to Congress in July 1965. The project was designed to protect the city from a standard hurricane for the region, which was roughly equivalent to a Category 3 hurricane on the Saffir-Simpson Scale. The standard hurricane was defined as high sustained wind speeds reasonably characteristic for a specified coastal location. Reasonably characteristic was defined as only a few hurricanes on record over the general region had been recorded to have more extreme wind and other meteorological characteristics. The standard hurricane was determined by the U.S. Weather Service.

Two months later in September 1965, Hurricane Betsy, a Category 3 hurricane, struck Louisiana's coast, causing damage in New Orleans. Congress authorized construction of the Lake Pontchartrain project in the Flood Control Act of 1965, enacted in October 1965. Modifications to the authorization have been made in subsequent legislation. Since that original design, there have been two major developments in the project relevant to current investigations into the floodwall failures: (1) the shift from the barriers at the inlets to Lake Pontchartrain to higher levees along the lake; and (2) the shift from floodgates at the mouth of the city's stormwater outfall canals that drain into Lake Pontchartrain to higher floodwalls along the length of the canals. These two decisions are discussed below.

Choosing Higher Levees over Inlet Barriers

The original July 1965 Lake Pontchartrain project design consisted of the Barrier Plan for constructing inlet barriers at Lake Pontchartrain's three main tidal entrances as well as levees and floodwalls for surge protection. The barriers generally would remain open and allow for navigation, and would close during coastal storms to reduce storm surges from entering the lake. Based on updated weather data and experience learned during the city's flooding in September 1965 by Hurricane Betsy, changes in the project were sought before construction began. For almost 2 decades, technical issues, environmental concerns, legal challenges, and local opposition to various components slowed construction.

The design that the Corps eventually chose was the High-Level Plan which consists of higher levees and floodwalls, instead of the originally planned inlet barriers and lower levees and floodwalls. ( Figure 2 shows the existing hurricane protection infrastructure as well as the elements of the Barrier Plan that were rejected in favor of higher levees and floodwalls.) The change from the Barrier Plan to the High-Level Plan was approved by the Corps' Chief of Engineers in February 1985; both the barrier and the high-level plans were designed to protect from the rough equivalent of a fast-moving Category 3 hurricane. The Chief's decision to adopt the High-Level Plan was based on a 1984 project reevaluation study conducted by the agency in response to a 1977 court injunction on the construction of inlet barriers until an adequate Environmental Impact Statement (pursuant to the National Environmental Policy Act of 1969 P.L. 91-190) was completed. The re-evaluation study recommended the change because "the High Level Plan has greater net benefits, is less damaging to the environment, and is more acceptable to the public" than the Barrier Plan.

Choosing Improved Canal Levees and Floodwalls over Floodgates

To drain the city of stormwater (i.e., accumulated rainfall), the city pumps water into three outfall canals—the 17 th Street canal, the Orleans Avenue canal, and the London Avenue canal—that flow into Lake Pontchartrain. The pumps are located at the southern ends of the canals, away from the lake. To protect the city from rising water in Lake Pontchartrain during hurricanes, levees were built along the length of the canals. The levees along the outfall canals were considered adequate when the Corps developed the original design for the Lake Pontchartrain project that was sent to Congress in July 1965.

Subsequent to the U.S. Weather Bureau's adoption of a more severe standard hurricane for the region, the Corps determined that the levees along the outfall canals were inadequate in their height and stability to protect the city from the standard hurricane. The Corps eventually integrated hurricane storm protection for the canals into its Lake Pontchartrain project. The Corps considered Improved canal protection necessary regardless of the selection of the Barrier or High-Level Plan. The two basic canal options evaluated were:

"butterfly" floodgates at the mouths of the outfall canals that would close when water levels in Lake Pontchartrain exceeded levels in the canals (known as fronting protection); and higher and stronger levees and floodwalls along the canals (known as parallel protection).

The Orleans Levee District and the Sewerage and Water Board of New Orleans favored parallel protection over floodgates; they were concerned that the operation of the butterfly floodgates would reduce the ability to pump stormwater out of the city during storms. The Corps analyzed the options and recommended parallel protection for the 17 th Street Canal; in contrast, the Corps recommended butterfly floodgates for the Orleans and London Avenue canals. The Corps concluded that the butterfly floodgate plan for the London Avenue canal

fully satisfies the project's mandate to provide protection against the hurricane generated tidal surges and yet provides the maximum latitude for operation of local interest interior drainage [i.e., stormwater removal]. The butterfly control valve plan has been shown to be the least costly fully responsive plan. When compared to the parallel protection plan it is approximately three times less costly.

The conclusion for the Orleans Avenue canal was similar; the Corps found the butterfly gates to fully satisfy the project purpose of hurricane storm surge protection and to be one-fifth the cost of parallel protection.

Rather than having the Corps proceed with construction of the butterfly floodgates, the Orleans Levee District decided to construct on its own most elements of the parallel protection on the Orleans and London Avenue canals. This local construction was designed in accordance with Corps criteria, so that the parallel protection would be incorporated into the larger Lake Pontchartrain project. ( Figure 2 shows the existing hurricane protection infrastructure as well as the canal floodgates that were rejected in favor of higher canal levees and flood walls.) The Corps recommended that the federal cost-share contribution for the parallel protection of the two canals be capped at 70% of the less-costly butterfly floodgates design. (The Lake Pontchartrain project was authorized in 1965 based on a construction cost share of 70% federal - 30% nonfederal. See the Appendix for a 40-year history of the federal construction funding.) In H.Rept. 101-966, the Conference Report for the Water Resources Development Act (WRDA) of 1990 ( P.L. 101-640 ), Congress directed the Corps to consider favorably parallel protection for the two canals and for the federal government to bear part of the costs, but did not specify what percentage of the cost. This report was followed by the Energy and Water Development Appropriations Act of 1992 ( P.L. 102-104 ) in which Congress stated:

The Secretary of the Army is authorized and directed to provide parallel hurricane protection along the entire lengths of the outfall canals and other pertinent work necessary to complete an entire parallel protection system, to be cost shared as an authorized project feature, the Federal cost participation in which shall be 70 percent of the total cost of the entire parallel protection system, and the local cost participation in which shall be 30 percent of the total cost of such entire parallel protection system.

Current Issues and Conclusion

In summary, the original project design aimed to control storm surge flowing into water bodies around downtown New Orleans using inlet barriers and canal floodgates (in combination with levees). The constructed project, however, attempted to reduce the city's flooding from water bodies affected by hurricane storm surge and wind through higher levees and floodwalls. The Corps' decision to recommend higher levees instead of inlet barriers was shaped by multiple factors, including environmental litigation, project economics, and local preferences. The Corps preferred floodgates to floodwalls along the Orleans Avenue and London Avenue canals. The decision to not build floodgates, and instead build floodwalls along the canals, was made by the local project sponsors. The original design and the final design were intended to provide the same level of protection, i.e., protection from the rough equivalent of a Category 3 storm surge.

Hurricane Katrina's storm surge overtopped and breached New Orleans' hurricane protection system. In addition to causing extensive flood in downtown New Orleans, the floodwall failures decreased confidence in the reliability of the existing hurricane infrastructure to protect the city from Category 3 and less-severe hurricanes.

Confidence in both the reliability of hurricane infrastructure and the level of protection provided by natural and constructed hurricane protection is a factor shaping near-term and long-term investment decisions, as residents and businesses decide whether and how to rebuild. (For an analysis of wetlands restoration opportunities, see CRS Report RS22276, Coastal Louisiana Ecosystem Restoration After Hurricanes Katrina and Rita , by [author name scrubbed].) In the near-term, many are concerned with the level of protection that will be available at the start of the 2006 hurricane season. By June 2006, the Corps expects to have completed its repairs of the existing infrastructure. However, the findings from the Corps' investigation into the causes of the floodwall failures are not anticipated until June 2006, raising the question of whether the agency will be able to respond to the findings and improve the floodwalls' reliability when repairing the damaged levees and floodwalls for the 2006 hurricane season in June 2006.

Concerns about levee and floodwall reliability are compounded by concerns about the level of protection provided by the existing infrastructure given New Orleans' increasing vulnerability to hurricane storm surge. Land in the city has subsided; barrier islands and wetlands have been disappearing; and sea levels have risen. These factors have raised concerns about the ability of the city's infrastructure to provide Category 3 protection. According to the project justification sheet included in the Administration's Corps FY2006 budget request, "the project was initially designed in the 1960s, and a reanalysis was performed for part of the project in the mid-1980s. Continuing coastal land loss and settlement of land in the project may have impacted the ability of the project to withstand the design storm." The challenge of protecting New Orleans could become even greater. According to some scientists, higher sea surface temperatures may result in increased hurricane intensity. Climate change concerns and other factors have raised questions about whether both estimates of the likelihood of hurricanes of various strengths and past infrastructure investment decisions based on these estimates need to be re-evaluated.

Hurricane Katrina has resulted in some questioning why a Category 4 or 5 hurricane protection system was not in place for New Orleans, and whether it should be part of the rebuilding effort. The Corps currently only has congressional authorization for a Category 3 system; additional congressional authorization would be necessary to build a more protective system. Discussions of Category 4 or 5 protection for the city often include the extent to which coastal wetlands restoration may play a role in reducing the city's vulnerability to storm surge and whether some of the regional navigation improvements may increase storm surge vulnerability. These discussions raise broader policy issues related to the appropriate level of investment to protect against low probability-high consequences events; to protect against loss of life and economic disruption; and whether structural storm and flood control measures provide a false sense of security in vulnerable areas like New Orleans. The Corps' cost estimates are $1.6 billion to return coastal Louisiana's federal levees and floodwalls to pre-Katrina conditions by June 2006, and an additional $3.5 billion to increase protection for New Orleans from Category 3 to Category 5. State officials have estimated the cost of Category 5 protection and wetlands restoration for all of coastal Louisiana as high as $32 billion. Most local stakeholders argue for the inclusion of coastal wetlands restoration in any plan to improve hurricane protection.

Neither a consensus nor proposed plans on how to improve hurricane protection for New Orleans or costal Louisiana in the aftermath of Hurricane Katrina have emerged. Discussions continue about the advantages and disadvantages of additional infrastructure compared to other policy options, such as protection and restoration of wetlands that attenuate storm surges, buyouts of structures on the most flood-prone lands, flood-proofing structures, and improvements to the flood insurance program. For a discussion of managing flood risks, see CRS Report RL33129, Flood Risk Management and Levees: A Federal Primer , by [author name scrubbed] and [author name scrubbed].

Understanding why the hurricane protection system failed in New Orleans is essential to moving beyond simply making repairs, to identifying and reducing vulnerabilities in the system, addressing coastal wetlands loss, and rebuilding the city. Nonetheless, the Corps is having to proceed with available information in order to perform repairs to the failed floodwalls and other breaches to meet the June 2006 deadline, which marks the start of the hurricane season. Consequently, congressional oversight of New Orleans' hurricane protection is likely to continue as the nation grapples with decisions on what type and level of hurricane protection to provide New Orleans and other coastal areas around the nation, and who should bear responsibility and costs for protection in coastal, floodplain, and other hazard-prone areas.

Appendix. Lake Pontchartrain Project Federal Funding—1965-2006

Table A-1 provides the federal funding history for the constructions of the Lake Pontchartrain project. This information was provided to CRS by the Army Corps of Engineers. Table A-1 does not include project funding by non-federal project sponsors which are responsible for 30% of construction expenses and 100% of maintenance costs.

The Initial Work Allowance column represents the final enacted amount; this amount differs from the amount shown for the Lake Pontchartrain line item in appropriations conference reports due to rescissions and other reductions made by Congress. The Corps has some authority to reprogram funds across construction projects during the fiscal year; the Year End Work Allowance represents the Initial Work Allowance and any reprogrammings that occurred, which are shown in the Transferred Funds column. A negative in the Transferred Funds column indicates funds were reprogrammed away from the Lake Pontchartrain project during the fiscal year.

Beginning with the Fiscal Year 1994 Budget Justification, the Corps stopped scheduling the Orleans Avenue and London Avenue components of the Lake Pontchartrain project as part of its annual budget request. As shown in Table A-1 , Congress provided more than requested for the Lake Pontchartrain project by the Administration. Some of these funds may have been used to construct parallel protection for Orleans Avenue and London Avenue canals; however, CRS was not able to determine the federal funding level for the Orleans Avenue and London Avenue parallel protection based on currently available information. When Hurricane Katrina hit, the floodwalls along all three canals were complete; the canal work that remained to be built was the floodproofing of bridges (that is, the extension of a floodwall across a bridge to connect with a floodwall on the other side) and the extension of floodwalls across the front of pumping stations.