Little has been reported about the storm surge that occurred in the Mississippi River.
The simulation also indicates Katrina pushed a substantial storm surge up the Mississippi River, rising close to the top of river levees in the New Orleans area and even overtopping them at one point in Algiers.
To the east, as the storm itself moves closer to New Orleans, the model shows northeasterly winds pushing a wall of water directly against one hurricane levee and over the top, flooding St. Bernard Parish and New Orleans' Lower Ninth Ward. Photographs and surveys show that levee took heavy damage in the storm.
New Orleans was virtually surrounded by Hurricane Katrina's storm surge. From the south, it came from the Mississippi River. From the east it came from Lake Borgne and the marshlands, and from the north, Lake Pontchartrain.
New Orleans did suffer from the affects of Katrina's storm surge:
The figure to the left(above, ed) is the most accurate model available of the storm surge. It missed New Orleans and the maximum impact was along the Mississippi Coast. Note the submergence of the entire outer delta except the levees and jetty, especially along the west side of the Mississippi River. Note also how the Lake Pontchartrain Causeway intensified the surge at New Orleans.
This computer model at the Advanced Circulation Development Group shows the storm surge as Katrina came ashore. It also shows how the wind pushed the storm surge to the north shore of Lake Pontchartrain and then south toward New Orleans.
Not only was New Orleans threatened by Katrina's storm surge but rainfall was a factor. Since the majority of New Orleans is below sea level, pumps are used extensively during rain fall. Because of power failures, these pumps were inoperative. These pumps usually direct the water into Lake Pontchartrain.
The force of a storm surge cannot be discounted. From my understanding, the levees along the south shore of Lake Pontchartrain began to fail about the time the winds from Hurricane Katrina started coming from the north. All the water built up in the lake from Katrina's storm surge was heading south east toward New Orleans.
Mississippi received the burnt of Katrina's storm surge. Two and half years later, I still see the affects everyday. A massive wall of water extending from the Mississippi River to the Florida panhandle inundated coastal Mississippi and the New Orleans area.
The inland penetration of Katrina's storm surge was truly remarkable. The Mississippi River levee system held and confined most of the surge east of the river except for the landfall region of Buras, LA. Regions west of the Mississippi River experienced little surge, suggesting that the river levee system may have augmented Katrina's surge on the east side. Most of Plaquemines, St. Bernard, and eastern Orleans Parishes were inundated with surge which overflowed levees and destroyed them with scouring action. Buildings outside the levee system became cement slabs. Tide gauges also show the surge traveled up the Mississippi River, with elevation spikes reaching 14 feet at the Bonnet Carre Spillway 10 miles west of New Orleans. Levees along some canals south of Lake Pontchartrain were not overtopped but experienced failures that are still under investigation, causing well-publicized flooding of New Orleans. The surge also penetrated through inoperative flood pumps which, when combined with the inability to remove rainwater, caused moderate flooding in the suburban region west of New Orleans. The eastern end of St. Tammany Parish suffered an extreme surge which came from Lake Borgne as well as up the Pearl and Bonfouca river systems, traveling miles inland in Slidell. St. Tammany's surge was associated with the wind shift as Katrina moved inland, sloshing piled-up water in Lake Pontchartrain northeastward.
There were many factors at play when Hurricane Katrina struck New Orleans. The surge in the Mississippi River, the surge on the eastern side of New Orleans, and the surge that impacted the levees New Orleans north. Also, the pumps were not working and could not deal with the rain water that fell in the city.
The failures of the levees are still being investigated. There is one thing that is not in doubt: Katrina's storm surge was massive and unprecedented. Water is a force. And due to the topography of New Orleans, that water had no place to go. Maybe when future studies come at, the physical force of all that water will have been measured.
It is the nature of water to flow to the lowest level. Most of New Orleans and the surrounding area is below sea level. Something had to give and just perhaps that is what caused the levee failures. It is interesting to note that the levees along the Mississippi River seemingly trapped the storm surge and did not allow that water to naturally flow back into the Gulf of Mexico.
Because of the possible role of the Mississippi River levee system trapping the surge, simulations are underway to examine the surge evolution if there was no levee. In addition, Louisiana has experienced extreme wetland erosion in the last 50 years. ADCIRC simulations of Katrina with Louisiana's wetland topography from 1920 and 1970 are in development. These sensitivity experiments will be shown at the conference.
It will interesting to see those results. Unlike the Mississippi Gulf Coast, when Hurricane Katrina passed on, the storm surge had no place to go except into the city of New Orleans itself.