The Lower Ninth Ward Levee Before and After Katrina

Before Hurricane Katrina, the Lower Ninth Ward levee system was a patchwork of earthen embankments and concrete I-walls lining the Industrial Canal and the Mississippi River-Gulf Outlet, built piecemeal over decades and never engineered for the storm surge that arrived on August 29, 2005. After the storm, the federal government spent nearly $15 billion rebuilding those defenses into the Hurricane and Storm Damage Risk Reduction System, replacing failed I-walls with stronger T-walls, adding a 1.8-mile surge barrier out in the marsh, and shutting down the shipping channel that had funneled the surge in. The before-and-after contrast is the difference between an underbuilt system assembled without a single responsible owner and a coordinated regional defense — a defense that is already losing elevation to subsidence and losing funding to political change.

The Levees Before Katrina

The Lower Ninth Ward sits in a bowl. The Industrial Canal, cut through the city between 1918 and 1923, severs the neighborhood from the rest of New Orleans and defines its western edge. The Mississippi River borders it to the south, the Florida Canal and Intracoastal Waterway to the north, and St. Bernard Parish to the east. Municipal drainage of the backswamp caused the land to subside, so that the lowest areas sat about four feet below sea level before Katrina.¹

Protecting that bowl were earthen levees topped in many places by concrete I-walls, thin reinforced slabs anchored by sheet piles driven into the ground. The system had grown in pieces over decades. No single entity was responsible for it, and it had not been subjected to rigorous external peer review. Funding pressures had pushed designers toward low-cost solutions.²

Several specific problems were baked into the pre-Katrina walls. Builders had used an incorrect vertical datum when measuring elevations, so many levees stood one to two feet lower than their intended design height. Designs did not account for ongoing subsidence, even though the region was known to be sinking. Along the Industrial Canal, the walls had been designed with an insufficient margin of safety, and engineers had overestimated the strength of the soft, organic marsh soils beneath them.²

Alongside those levees sat the Mississippi River-Gulf Outlet, a 77-mile shipping channel completed in 1968 that connected the Port of New Orleans to the Gulf. By 2003 commercial traffic had dwindled to about seven ships a day, but the channel’s physical footprint had grown. Erosion widened its banks from 500 feet to nearly 2,000 feet in places, and roughly 31 square miles of protective wetlands had been destroyed.³ MRGO was, in effect, a storm surge highway pointed at the Industrial Canal.

A Warning Already Delivered: Betsy, 1965

Katrina was not the first time these levees failed. In September 1965, Hurricane Betsy drove storm surge through the Intracoastal Waterway and the Industrial Canal, overtopping and breaching levees and submerging the Lower Ninth Ward and St. Bernard Parish under six to twelve feet of water while the rest of the city stayed relatively dry. After Betsy, the federal government ordered the Army Corps of Engineers to take responsibility for rebuilding and maintaining the levee system around New Orleans. The underlying vulnerabilities — the below-sea-level elevation, the ring of canals, the thin flood defenses — went largely unaddressed over the next four decades.⁴

How the Levees Failed on August 29, 2005

Katrina generated a 28-foot storm surge and 55-foot waves offshore.⁵ The Lower Ninth Ward was hit from three directions in rapid succession.

Between 4:30 and 5:00 a.m., levees at the CSX Railroad crossing on the northern arm of the Industrial Canal breached after storm surge broke through sandbags. Before 6:30 a.m., levees fronting MRGO were overwhelmed and destroyed, and water from those breaches reached the Lower Ninth Ward. Surge in the “funnel” where the Gulf Intracoastal Waterway meets the Industrial Canal overtopped the levees along its banks at the same time. By 6:50 a.m., water was also topping the Industrial Canal levees themselves. Investigators later called it a triple hit.⁶

At about 7:45 a.m., the levee along the eastern side of the Industrial Canal’s southern arm failed catastrophically. A 900-foot section of concrete I-wall near Claiborne Avenue collapsed, releasing a 20-foot head of water that destroyed nearby houses. A barge drifted through the breach and did further damage. Areas east of the breach flooded to twelve feet above sea level, and homes for several blocks were ripped from their foundations and scattered, usually in splinters.⁶⁷

The walls had been designed to withstand a surge of at least 11.2 feet. They failed at a maximum surge of approximately 10.5 feet.⁶

Why They Failed

Post-Katrina reviews by the American Society of Civil Engineers and other panels found a web of engineering and institutional failures. The I-walls were designed with an insufficient safety margin. Engineers had not accounted for a water-filled gap that opened behind the walls as they bowed outward under pressure, which increased stress on the soil foundation. The strength of the soft marsh soils beneath and beside the levees had been overestimated.²

At the Industrial Canal, the initial I-wall failure south of the Florida Avenue bridge happened while water was still below the top of the wall. Water had seeped beneath the structure, causing it to shift and fail.⁸ Other sections failed after overtopping water scoured and eroded the unprotected soil on the land side.

MRGO amplified everything. During Katrina, the convergence of MRGO and the Gulf Intracoastal Waterway produced water flow speeds nearly three times those in Lake Borgne, funneling surge straight toward the Industrial Canal.³

The consequences lasted long after the water came in. Because of the bowl topography, floodwaters stayed trapped for weeks, and it took 53 days to remove 250 billion gallons of water from the city.⁵ The Lower Ninth Ward was the last neighborhood to have drinking water restored, 14 months after the storm, compared with two months for the rest of New Orleans.⁹

What the Government Was Held Liable For

Lawsuits against the federal government were consolidated under In re Katrina Canal Breaches Consolidated Litigation in the U.S. District Court for the Eastern District of Louisiana. In November 2009, after a 19-day bench trial, Judge Stanwood Duval Jr. ruled that the Army Corps had failed to maintain MRGO. The court found that the Corps had recognized from the channel’s inception that its soils were prone to erosion yet had not installed authorized foreshore protection in time. The named plaintiffs were awarded $720,000.¹⁰

In September 2012, a three-judge panel of the U.S. Fifth Circuit Court of Appeals ruled that the Corps could not be held liable, invoking the discretionary function exception of federal tort law and concluding that the Corps’ decisions on levee construction and maintenance were “grounded in social, economic, and political policy.” Independent studies from UC Berkeley and ASCE had concluded the flooding was a “man-made catastrophe,” but the legal immunity held.¹¹ No federal money changed hands over the engineering failures themselves.

The Levees After Katrina

The post-Katrina Hurricane and Storm Damage Risk Reduction System (HSDRRS) represents a nearly $15 billion federal investment and a fundamentally different approach to flood defense. The Corps restored the system to pre-Katrina conditions by the 2006 hurricane season and then spent years rebuilding it with major upgrades. The final major project, permanent canal closures and pumps on the outfall canals, was completed in May 2018.⁵

Walls Rebuilt to a Different Standard

Many of the I-walls that failed during Katrina were replaced with T-walls, sturdier reinforced concrete structures supported by sheet piles driven deeper into the earth, with foundation piles set at angles for added stability. Standards for the soil used in levee construction were raised. Transition zones where floodwalls meet earthen levees were armored to prevent the scouring that destroyed so many sections in 2005.¹²

A New Line of Defense Out in the Marsh

The centerpiece is the Inner Harbor Navigation Canal–Lake Borgne Surge Barrier, a 1.8-mile structure built at the confluence of the Gulf Intracoastal Waterway and MRGO, roughly 12 miles east of downtown. It was completed in 2013 at a cost of $1.3 billion. The barrier stands 25 to 26 feet above sea level and is supported by 1,071 “soldier” pilings extending 140 feet underground, along with 240-foot battered piles. It includes a 150-foot-wide sector gate, a bypass barge gate, and a 56-foot-wide vertical lift gate.¹³ The barrier is designed to block storm surge before it can reach the Industrial Canal and the Lower Ninth Ward. In 2005, no such structure existed.

At the canal’s north end, a new Seabrook Floodgate Complex works with the surge barrier to prevent Lake Pontchartrain surge from pressurizing the canal.¹⁴ On the West Bank, the Gulf Intracoastal Waterway West Closure Complex houses what the Corps describes as the world’s largest drainage pumping station, capable of moving 19,140 cubic feet of water per second. Gates were installed on the 17th Street, London Avenue, and Orleans Avenue canals, the drainage canals whose failures flooded other parts of New Orleans in 2005.¹²

MRGO Shut Down

Congress ordered the Corps to study MRGO’s deauthorization in 2006, and the channel was officially deauthorized as a federal navigation project on June 5, 2008. A closure structure was built at Bayou La Loutre. An ecosystem restoration plan targeting approximately 57,472 acres, including cypress swamp, marsh creation, and 71 miles of shoreline protection, was authorized under the Water Resources Development Act of 2007.¹⁵ The hurricane highway that pointed at the Industrial Canal is closed.

Risk Reduction, Not Protection

The Corps deliberately rebranded the new infrastructure as “risk reduction” rather than “hurricane protection,” acknowledging that no levee system guarantees absolute safety. A Munich Re analysis found that HSDRRS is designed to reduce direct property damage by 90 percent for a 100-year flood event and potential loss of life by up to 97 percent compared with pre-Katrina conditions.¹⁶ Engineers have described the post-Katrina system as the “first time New Orleans has ever had a complete approach to dealing with water.”¹⁷ The system held during Hurricane Isaac in 2012 and Hurricane Ida in 2021.

Where the New System Stands Now

The rebuilt levees are the best New Orleans has ever had, and they are also sinking. Parts of the region are subsiding by nearly two inches per year, and sea levels are rising by roughly half an inch annually.¹⁷ A 2025 study published in Science Advances found that post-Katrina flood protection walls are losing up to 28 millimeters of elevation per year.¹⁸ Research from Tulane University suggests that even major concrete structures like the Lake Borgne Surge Barrier may be sinking.¹⁹

The Corps maintains that the system can provide 100-year protection through 2057, but only if it receives sufficient funding to periodically lift earthen levees to compensate for subsidence.¹⁷¹⁹²⁰

A separate project could reshape the Industrial Canal defenses again. The Army Corps is advancing a $4.7 billion plan to replace the century-old Industrial Canal lock, first authorized by Congress in 1956 and never completed. The proposed new lock would be 900 feet long and sit about 2,400 feet north of the existing structure, requiring realignment of floodwalls and levees along the canal.²¹ A draft General Reevaluation Report and Supplemental Environmental Impact Statement were released in May 2025, with the public comment period extended through September 2025.²² Critics say the project would leave existing flood defenses exposed for over a decade during construction and could allow Mississippi River storm surges to penetrate roughly a quarter-mile deeper into the Lower Ninth Ward. Internal EPA emails have raised concerns about increased flooding and pollution risks. The Corps has proposed approximately $480 million in community mitigation projects and maintains the lock replacement is the “least environmentally damaging practicable alternative.”²³

The before-and-after picture is sharper than it looks at first glance. Before Katrina, the Lower Ninth Ward sat behind walls that no one owned end to end, built on soils no one had measured honestly, with a shipping channel aimed at its back door. After Katrina, it sits behind a coordinated system with a surge barrier out in the marsh, stronger walls at its edge, and the shipping channel closed. The open question is whether the institutions that built that system will keep it standing as the ground sinks beneath it.

1
Rich Campanella. Urban History of the Lower Ninth Ward
2
LSU Law Center. External Review Panel Report
3
UC Berkeley Law Library. MRGO Analysis
4
Organization of American Historians. Hurricane Betsy and the Ninth Ward
5
U.S. Army Corps of Engineers. HSDRRS Risk Reduction Plan
6
PBS NOVA. How New Orleans Flooded
7
Organization of American Historians. The Forgotten People of New Orleans
8
New Orleans Historical. Industrial Canal Levee Failures
9
Washington Post. Katrina One Block
10
U.S. District Court, Eastern District of Louisiana. In re Katrina Canal Breaches Consolidated Litigation
11
Christian Science Monitor. Army Corps Not Liable for Katrina Damage, Appeals Panel Finds
12
Fox 8 Live. A Look at New Orleans Storm Surge Defenses 20 Years After Hurricane Katrina
13
Flood Protection Authority. Lake Borgne Surge Barrier
14
U.S. Army Corps of Engineers. HSDRRS Infrastructure
15
U.S. Army Corps of Engineers. History of MRGO
16
Munich Re. Flood Protection Improvement in New Orleans
17
Grist. Katrina Levees
18
Science Advances. Vertical Land Motion in Greater New Orleans
19
Louisiana Illuminator. Katrina Levee
20
Fox 8 Live. Concerns Raised About Flood Protection Authoritys Readiness for Hurricane Season
21
U.S. Army Corps of Engineers. IHNC Lock Replacement
22
U.S. Army Corps of Engineers. IHNC Lock Replacement Public Review Comment Periods Extended
23
Mother Jones. Katrina Lower Ninth Ward Canal Expansion