Hurricane Katrina and GIS

Topography-based Analysis of Hurricane Katrina

Inundation of New Orleans

This article (Gesch, 2007) discusses Hurricane Katrina and the methods, such as topography, that were used to determine the elevation and flooding of the city of New Orleans, and how those methods were used in the aid of people in the city after the catastrophic hurricane of 2005. To fully understand this article, however, background research on New Orleans and hurricanes needs to be discussed to comprehend the devastation of the city and the reasons behind it.

Inundation, or flooding, is a major problem for cities located near large bodies of water, as well as places that are of low elevation. When a hurricane strikes, the storm surge is thrust in front of the storm. This is due to the ocean water being pushed towards the shore of a coastline by the force of the winds from the hurricane moving cyclonically around the eye of the storm.

Some factors can affect the intensity of a storm surge, such as the slope of the ocean floor leading up to land. A shallow slope usually leads to a more intense storm surge versus the slope of a steep shelf. This can be shown in the impact of the same intensity hurricane in two diverse areas. The shallow slope of the Louisiana coastline and the steep slope of the Florida coast would make a hurricane of the same strength produce a potentially 20 foot storm surge in Louisiana, and only a 8 foot storm surge in Florida.

Storm surge, according to NOAA (the National Oceanic and Atmospheric Administration), is often the deadliest component of a hurricane, and usually causes the most damage to property as well. This can inundate the coastline, causing major flooding events in areas that might not even flood normally. Hurricane Katrina produced the highest storm surge ever recorded on the U.S. coastlines, a catastrophic 27.8 feet (NOAA.gov). This completely devastated the city before the full brunt of the storm had even reached landfall, producing more rain to even further flood New Orleans. 

New Orleans, Louisiana is extremely prone to flooding for a variety of reasons. First, the city itself sits at the base of a bowl. The city itself is an average of about 1 to 2 feet below sea level. Thus, water is prone to sitting in the bowl and not draining out. In addition, water is even more prone to entering the bowl of the city because the city has major bodies of water on either side. Lake Pontchartrain, Lake Borgne, and the Mississippi River surround the city and are actually elevated above the city, and are held back but natural and man-made levees (as displayed in the figure above from Gesch, 2007). Thus, when water is poured into those bodies of water, they overflow into the city and flood it. New Orleans is also located at the southeastern tip of Louisiana, so it is near the ocean, where the hurricane will strike it at maximum intensity.

LIDAR is light detection and ranging, and a method discussed in Gesch’s (2007) article. Geographical data, especially topographic data, is very important for the success of the response and recovery groups during a large-scale natural disaster. The availability of high-resolution and high-accuracy elevation data originated from the LIDAR technology made it easy for rescue crews to estimate the flooding in different parts of New Orleans from Katrina in 2005. The days immediately after the storm, it was easy to find the areas that were in the most need of rescue crews, and were the most flooded. It also assisted in estimating the actual floodwater volume contained in the city. There is even potential for the influences of both the depth and length of flooding to be calculated on diverse types of structures in New Orleans.

Furthermore, this data assists in ongoing and future studies about the impacts of the storm and storms like it, and any potential imminent hurricane impacts on the city. With articles and GIS methods implemented such as these, the loss of life and property can be mitigated as much as possible for hurricanes like Katrina in the coming years. 

Resources: 

Gesch D (2007). Topography-based analysis of Hurricane Katrina Inundation of New Orleans. In: Science and the storms: The USGS Response to the Hurricanes of 2005. United States Geological Survey, Reston

NOAA.gov