Monday, September 15, 2014

Could Katrina have made more damages without Lidar ?

A long time has gone by since the devastating Hurricane Katrina. Nevertheless, New Orleans still carries the stigmatisms of that dark day of August 29th 2005.  What if we move back to August 2005 to learn a little bit more about the behind the scene of that event.

At this time, a mapping tool, Lidar, was used to collect information about the topography of inundation in New Orleans. Based on “a high level of spatial detail and vertical accuracy of elevation measurements, light detection and ranging remote sensing is an excellent mapping technology for use in low-relief hurricane-prone coastal areas”, according to Dean Gesch.  Thus, this high-resolution and high accuracy elevation data is more than useful when it comes to determine the flooding risk in cities, especially the coastal ones. Furthermore, it is useful for studies of the responses to impacts of storms. Indeed, this elevation data prove to be essential to determine the hurricane response and recovery activities. They can accurately establish a map of the different land-surface elevations within the city. In 2005 this tool, Lidar, even though was relatively new in the world of remote-sensing technology and because of its advanced technology, the U.S. Geological Survey used it for their National Elevation Dataset. New Orleans elevation data were updated in June 2005; therefore, they were already available for response to Katrina.
Figure 1: We can see the different elevation data of New Orleans. Red being the highest and blue the lowest.

Immediately after the levee breaches, there was a demand for a map showing the extent and magnitude of the flood waters in the city. The National Elevation Data proved to be a great help for mapping the extent and the depth of the inundation because no aerial imagery of the area were available at this period. Basically, knowing that the level of the Lake Pontchartrain and the flood waters equalized, the elevation was calculated from a lake-level gage on the lake and the data provided by Lidar. By its effectiveness and quickness to be realized, they could project the length of time required to remove the water from the city.


Figure 2: Map of the relative water depth for the New Orleans area.

If we compare the two figures, we can see that the most devastated part of the city could have been predicted as the lowest land-surface elevation on the first map represents the deepest flood waters on the second.

What if we change?
Unfortunately, Dean Gesch, the author of the article, does not provide any information if they used this tool to prevent environmental hazards, such as hurricanes. In any case, Lidar probably helped New Orleans’s mayor, Ray Nagin, to evacuate the most risky part of the city. However, we could analyze the use of the supposed-to-be-safe levee. Are they as safe as we think they are? Do they really prevent from flooding? Apparently this is not even an accurate question, when we see what happened in New Orlean. Of course levees provide an important source of safety, and category 5 hurricanes are not that common, but you have to be ready for the worse at anytime. Mother nature is not going to tell you months in advanced what she is up to. We know now that the levees were not strong enough to resist to this hazard and when you look at a transversal cut of New Orleans, you understand how it ended up like a vulgar swimming pool.
 Figure 3: Area map of New Orleans and its levees elevation.


To conclude, we could ask ourselves why do Men have to put themselves in a dangerous position? What if we stopped trying to change nature by adjusting to her? That is probably one of the longest debates that governments do not find enough time to talk about.

Reference: Topography-based Analysis of Hurricane Katrina Inundation of New Orleans By Dean Gesch, 2005. 
For Figure 3: http://en.wikipedia.org/wiki/New_Orleans#mediaviewer/File:New_Orleans_Levee_System.svg

3 comments:

  1. I reviewed the same post so I share some insights with you. I did not think of the point about using the LIDAR data to help plan out evacuation. I found that really interesting. I am now wondering if they ever use programs such as LIDAR along with supplemental information such as data taken from flood gauges in the period while the hurricane is traveling towards the landing site to predict things like flood rates and how to best evacuate the population. I hope they do so and protect the city my family lives in!

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  2. To add to Sam's comment, I think that the use of LIDAR would be a viable option for evacuation, especially if it were paired with another form of information, planning, or data retrieval. Maybe with the use of these forms of information, one could determine the most efficient evacuation route depending on a person's location and proximity to a safe zone.

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  3. I wonder how often LIDAR data is used in emergency response/planning. As the article asserts, it would be a very useful tool and I hope public departments are able to make use of it.

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