New Orleans Outfall Canals

An historical look at the City of New Orleans in 1878. The outfall canals were already constructed and included, from west to east, the 17th Street Canal, the Orleans Avenue Canal and the London Avenue Canal.

New Orleans was founded in 1718 by Jean-Baptiste Le Moyne, Sieur de Bienville, along the high ground adjacent to the Mississippi River (about 17 feet (5.2 m) above sea level). The city struggled early on with rainfall drainage because of the topography of the region.[12]

The Metairie and Gentilly ridges, both about 3–4 feet above sea level and located between the Mississippi River and Lake Pontchartrain, made it difficult for rainwater to move out of the city since the water would have to flow over these ridges in order to be drained northward into Lake Pontchartrain. Bayou St. John, a natural bayou and old navigation channel that ran from the northern edge of the French Quarter north to Lake Pontchartrain (today it runs from the Mid-City neighborhood to Lake Pontchartrain), was not enough to drain the often heavy rainfall that occurred.

With drainage and rainfall-related flood protection a huge concern, man-made canals were constructed by the mid-19th century. Drainage machines and pumps were built to lift the drained water over the high ridges and into the outfall canals. By 1878, there were approximately 36 miles (58 km) of drainage canals feeding into Lake Pontchartrain to remove rainwater from populated areas. Today there are 90 miles (140 km) of covered drainage canals, 82 miles (132 km) of open channel canals and several thousand miles of storm sewer lines that feed into the system.[13]

These early primary drainage canals included (from west to east): 17th Street, Orleans Avenue and London Avenue. As the population expanded northward toward the lake, low-lying swamps were reclaimed by constructing shallow drainage ditches that fed into the newly created system of drainage canals. However, the reduction in the groundwater table, as a result of the drainage and reclamation of swamps and marshland, produced significant land subsidence in the drained area. That land subsidence continues today.

The construction of the outfall canals did have another major consequence. By digging canals through the Metairie and Gentilly ridges, the canals opened up storm surge avenues into the heart of New Orleans via Lake Pontchartrain.

A hurricane in 1947 overwhelmed the existing levees along the outfall canals. Here, the 17th Street Canal is breached by a hurricane storm surge.

The New Orleans Sewerage and Water Board, which was established in 1899, became the primary agency that tackled the tough drainage problems facing New Orleans. Flood protection levee upkeep, including those along the outfall canals, was done locally by the Sewerage and Water Board and the Orleans Levee District, the latter of which is a state agency established in 1890 to handle the operation and maintenance duties associated with levees, floodwalls, and other hurricane and flood protection structures surrounding the city of New Orleans.

In 1915 and again in 1947, devastating hurricanes struck the New Orleans area, causing millions of dollars in property damage and killing hundreds of residents. Water overtopped and breached the levees along the outfall canals and the Sewerage and Water Board and the Orleans Levee District raised the levees an estimated three feet after those hurricanes. However, some of these levees had subsided by as much as 10 feet (3.0 m) during their nearly 100-year existence.

The first federal involvement with hurricane protection in New Orleans began in 1955 with Public Law 71 of the 84th Congress, 1st Session, when Congress authorized the Secretary of the Army to examine and survey the eastern and southern seaboards of the United States, with an emphasis on those areas where severe hurricane damages had occurred in the past. This authorization was granted after several hurricanes in 1954 severely damaged portions of the eastern and southern U.S. Although this authorization marked the first federal involvement with hurricane protection in the city, it authorized only a feasibility study and did not authorize or fund any construction-related activities.[14]

The Lake Pontchartrain & Vicinity system, which includes much of southeast Louisiana.

As part of the authorization, the New Orleans District of the U.S. Army Corps of Engineers examined the Lake Pontchartrain and Vicinity area of coastal Louisiana, which includes most of St. Bernard Parish, Orleans Parish east of the Mississippi River (including most of the City of New Orleans), Jefferson Parish east of the Mississippi River and a small portion of St. Charles Parish east of the Mississippi River. The Lake Pontchartrain and Vicinity area encompasses one large natural drainage basin that today includes the Orleans Metro sub-basin.

After seven years of planning, the New Orleans District produced an Interim Survey Report, which was transmitted by the Secretary of the Army to the U.S. Congress in November 1962. This report outlined a comprehensive plan for preventing flooding in the greater New Orleans area from a Standard Project Hurricane, which is a hypothetical hurricane representing the most severe combination of hurricane parameters that is reasonably characteristic of the area.

This report’s recommended protection plan for Lake Pontchartrain and Vicinity consisted of a barrier at the east end of Lake Pontchartrain. The barrier would include locks in the Rigolets and Chef Menteur Pass, as well as a lock in the Inner Harbor Navigation Canal at its confluence with Lake Pontchartrain (in the Seabrook area). The locks would limit hurricane storm surges from entering Lake Pontchartrain and reduce high-salinity flows into the lake from the Gulf of Mexico via the Mississippi River-Gulf Outlet (MRGO), which was under construction at the time. As part of this original “Barrier Plan,” the existing levees along all three outfall canals were deemed adequate for hurricane protection purposes.

In September 1965, Hurricane Betsy struck the Louisiana coast near New Orleans, causing massive property damage and loss of life. While Betsy had similar characteristics of the Standard Project Hurricane, Betsy’s wind field and associated wave action called into question the adequacy of the original design heights for project levees and floodwalls outlined in the 1962 Interim Survey Report. As a result, the New Orleans District requested and received permission from the Corps’ Mississippi Valley Division and Corps Headquarters to increase levee and floodwall heights by 1–2 feet across the project network.

In addition, a Design Memorandum issued in 1968 revealed that the outfall canals needed to be addressed because the existing canal levees did not meet the design heights required by federal design criteria adopted after Hurricane Betsy. However, no immediate guidance was given as to how to increase flood protection along the canals and it remained an unresolved issue for over two decades.[15]

Congress authorized the post-Hurricane-Betsy-modified Barrier Plan when the Flood Control Act of 1965 was passed, positioning the federal government to assume 70 percent of construction costs. After authorization, the New Orleans District set out to develop detailed engineering plans, secure the required funding and real estate, and construct project features. The District initially estimated that the project would be complete by the mid-to-late 1970s.

State governmental elected officials, congressional representatives and various local citizen and interest groups met the Barrier Plan with opposition. Some opponents feared that the barrier would adversely affect navigation access to the lake, while others cited the possible flooding of the north shore of Lake Pontchartrain when the barriers were closed. Also a concern was potential operation and maintenance costs. It was the environmental effects of the barrier, however, that caused the most opposition.

As part of the National Environmental Policy Act (NEPA), the New Orleans District prepared an Environmental Impact Statement (EIS) to address the environmental impacts associated with the project and how the Corps would mitigate those impacts. In 1975, a local environmental advocacy group challenged the adequacy of the 4-page typewritten EIS in U.S. District Court.

Judge Charles Schwartz issued an injunction preventing further progress on the barrier option until the Corps revised its EIS. He also wrote, however, that upon proper compliance with NEPA, ‘the injunction shall be dissolved and any hurricane plan thus properly presented will be allowed to proceed’.[16]

In other words, the Judge invited the Corps to return with a more comprehensive EIS. Ultimately, however, the Corps did not return and, in 1980, concluded that an alternative option of higher levees providing hurricane protection was less costly, less damaging to the environment and more acceptable to local interests.[17]

Hurricane protection floodwalls are installed along the Inner Harbor Navigation Canal in 1968.

In 1985, the Director of Civil Works approved increasing levee heights along the lakefront. Construction of other non-barrier features continued as part of the original authorization. With the adoption of the High Level Plan, the New Orleans District could now move forward with providing hurricane and storm surge protection features along the lakefront and outfall canals.

Beginning in the late 1970s, the Corps’ New Orleans Board (OLB) began identifying and examining hurricane protection alternatives for the outfall canals. Through a series of Design Memorandums in the late 1980s and early 1990s, the Corps recommended building a prototype gate plan employing self-actuating butter-fly check valves at the Orleans Avenue and London Avenue canals. Butterfly gates are hydraulically operated gates that swing on a pivot and close if a storm surge threatens to enter the canals. (It is instructive to note that the gates alternative did not include auxiliary pump stations like those installed after Hurricane Katrina.)

For the 17th Street Canal, the cost of a butterfly gate structure was about the same as the cost of the locally preferred plan of higher parallel levees along each side of the canal, so the corps agreed to pursue “parallel protection” along that canal. There is no stated evidence in the project record that the corps felt that there were differences between the approaches in providing reliable surge protection (Woolley Shabman, 2–48).

However, for the much smaller capacity London and Orleans Avenue Canals, the corps preferred the gates-no-pumps plan because it was significantly less expensive. The parallel protection plan was estimated in the 1980s to cost three times more than the gates plan for the London Avenue Canal and cost five times more than the gates plan for the Orleans Avenue Canal.[18]

The OLB and the Sewerage and Water Board, however, favored parallel protection for the Orleans Avenue and London Avenue outfall canals because they believed interior drainage would be inhibited when the gates were closed during a tropical event because water would not be able to escape from the canals and into Lake Pontchartrain. As interior drainage was not part of the federal authorization for hurricane protection, the OLB and the Sewerage and Water Board would be responsible for any costs associated with pump installation at the mouths of the outfall canals. The OLB and Sewerage and Water Board contended that parallel protection could provide increased hurricane storm surge protection while maintaining interior drainage.

The Corps argued that the butterfly gates plan for the Orleans Avenue and London Avenue canals because they considered it their mandate to build projects with the most favorable cost benefit ratios. Cost was the pre-eminent factor. There is nothing in the project record indicating that the gates-only plan was the superior option, only that it was less expensive.[19]

For several years the project was at a stalemate. The local sponsor successfully lobbied Congress to direct the corps to implement the much more expensive parallel protection plan for all three outfall canals, not just the 17th Street Canal, in the Water Resources Development Act of 1990. Two years later, Congress stipulated that the federal government would pay 70 percent of the cost, with the local sponsor picking up the other 30 percent, in the Energy and Water Development Appropriations Act of 1992.

With the dispute over hurricane protection solutions for the outfall canals seemingly resolved, the Corps began designing and constructing predominantly “I-wall”-type floodwalls on top of the levee crowns. I-walls met the project goals of providing increased embankment heights within the limited existing rights-of-way with minimal disruption to the adjacent residential neighborhoods. Construction began in 1993, and project work along the outfall canals was reported to be nearing completion in 2005 prior to Hurricane Katrina.

Floodwalls were built instead of levees to protect against flooding because many homes, pictured here, back up to the levees. Any widening of the levees would be nearly impossible given the limited right of way.