17^th Street Canal and London Avenue Canal Breaches

At one point along the 17^th Street Canal and at two points along the London Avenue Canal, the levees were not overtopped but failed. The levees in this area are about 14 feet, but the water inside the canals was only at 8.5 feet. The canals were backed up with water from the storm surge coming from Lake Pontchartrain. The pumps in the canals were unable to pump the water out because the pumps were located below sea level in the section of the canal in the interior of the city, not near the lake. The levees along both canals are concrete I-walls atop earthen levees. The concrete walls were actually pushed aside by the water pressure building up inside the canals. The steel pilings driven into the soil were too shallow, and the soil foundations in which the concrete walls were anchored in were poor, too soft, and permeable. Water was able to seep through and undermine the foundations and wedge the wall from its foundations, causing the whole wall to be pushed over and water to enter the city. The canals, which are supposed to pump water out of the city, actually caused much of New Orleans to flood by letting water into the city. The breaches at the 17^th St. Canal and London Avenue Canal were caused by engineering failures. The levees were built on top of poor soil and sand, the pilings were not deep enough, and the pumping system was designed poorly. (IPET)

Funnel Effect, Industrial Canal Breach, and Flooding in the Lower Ninth Ward, St. Bernard Parish, and New Orleans East

A storm surge many feet higher than predicted for a Category 3 storm preceded Hurricane Katrina into New Orleans. It came down the Mississippi River Gulf Outlet (MR-GO). It then entered the Intracoastal Waterway . While in the MR-GO and the Intracoastal Waterway, the storm surge overtopped the earthen levees along St. Bernard Parish to the south and New Orleans East to the north. The overtopping of the levees caused erosion on the backside of the earthen levees as water came spilling over, weakening the system even more.  The Intracoastal funneled the storm surge into the Industrial Canal where it met up with storm surge coming in from Lake Pontchartrain. The levees with concrete floodwalls on the Industrial Canal were breached once on the west side into Bywater and twice on the east side into the Ninth Ward, where some of the worst flooding occurred. All of the levees in this area were overtopped. The water was 1.7 feet above the 13-foot levee. The overtopping eroded the levee on the protected side, letting more water pour in. However, some evidence shows that the initial flooding of the Ninth Ward occurred before the levees were overtopped. The levee was built on top of marsh which was on top of clay which in turn was on top of sand. A gap, or wedge, formed on the canal side of the levee between the wall and the marsh foundation, increased the water pressure on the wall, and caused it to fall over and flood the Ninth Ward. (IPET)

Many of the levee breaches occurred where two different types of levees were joined together. At these joints of two different kinds of materials the weaker one would fail. This is why standardization of levees will be key in the solution. In the past, different groups built on top of each other’s work at different times causing discontinuities in the system. (IPET)