This is not a simple Park and grab cache. Earth caches are designed to make you think about Geology and Geologic events. Please print off this sheet to have it with you while you go to the levees so that you can answer the questions. I will remove you post if you can not answer the questions.
New Orleans Levee Breaches Part I
A. 17’th Street Canal
B. London Canal
C. Mystery Levee Breach on the Orleans Canal ( not marked on the map because it is not a "true" breach )
Coordinates:
A. N 30° 01.019 W 090° 07.230 : 17’th Street Canal
B. N 30° 01.237 W 090° 04.287 : London Canal
C. N 29° 59.708 W 090° 06.050 : Mystery Levee Breach on the Orleans Canal
If you do both of the Levee EarthCaches plan on the trip taking over a hour, possibly several hours if you take time to look around at devastation caused by the failure of the levees within New Orleans. This is a daytime only cache, I would not walk around these areas after dark ( the national guard still patrols the area ). Since this is a geologic cache, you will be tested on your observations at the end. Due to on-going construction at some of these locations, I did not post the exact coordinates of the breach. Rather, you will be on a sidewalk right in front of the new levee wall.
You are free to walk around in these areas and I would encourage it, but if you do please be considerate. Every family around here lost everything they had. Some even lost family members due to the flood.
This is just a very brief over views of the levee failures. For detailed information, please see the references.
Hurricane Katrina levee breaches in New Orleans
Hurricane Katrina struck the birds foot of the Mississippi the morning of August 29, 2005 near Buras La. It came ashore with wind speeds of 125 miles per hour, making it a category 3. Luckily, the winds diminished from category 5 strength only 24 hours earlier. Storm surge in the gulf was 18-23 feet which topped the levees in St Bernard Parish. Within the New Orleans city limits neither the river levee nor the lake levees were breached during the storm. There was major topping of the lake levee in Eastern New Orleans, and a smaller amount north and west of the city. None of the drainage canals in the interior of New Orleans were "officially" topped, but the levee breaches (Figure 1.) and overtopping of the Industrial Canal and lake levee allowed the water to inundate the city. In all 85% of the city was flooded as a result of the levee failures and overtopping.
Figure 1. Map of New Orleans showing the major levee breach locations.
Location A and B : Ground Heave/Faulting : London Canal and 17’th Street Canal
When the city of New Orleans was originally founded in 1718 by the French Mississippi Company, the land around Lake Pontchartrain was swamp. As the population grew, the swamp was drained and houses were built on a thin layer of dirt placed on top on the swamp deposits. Before colonization, over the previous several hundred years layers of peat and swamp deposits built up. These swamp deposits are not stable and can break apart easily. Water in the canals placed tremendous outward pressure on the levees. This outward force caused the peat and swamp deposits to become unstable and act as a fault plane. This fault or (glide plane) allowed a 200+ ft section of the levee to be displaced laterally about 45 ft ( figures 2 and 3 ). Normally, the Swamp deposits are between 8 to 15 feet underground but due to the horizontal faulting of the ground, these peat and swamp deposits were "heaved" or pushed up to the surface. Before the debris was removed from the Lake View neighborhood, large blocks of the peat were seen sitting on the surface. There were also several reports from people who lived next to the levee of water seeping into their back yard months, even years before the breach. These seeps could have been a clue that water was making its way under the sheet piling used to stabilize the ground under the levees. Nothing was done about these water seeps.
Figure 2. Diagram of a possible explanation of how the 17’th street levee failed. An eye witness said that the levee wall started to lean and 6:30 in the morning even before the storm passed the city. This could have caused water to come in contact with a weak peat layer running under the sheet piling. Some combination of the water soaked peat and the outward pressure on the levee caused a 200+ ft section of the levee to be displaced laterally 45 feet between 8:30 and 9:00 in the morning.
Figure 3. View of the 17’th street canal looking to the south. Notice the portion of the levee that was pushed out of place during the breach. Notice the trees growing on the levee. Tree roots would provide stability to the soil, but during a large storm, the ground could become saturated with water. The wind can push over the trees which would tear out large sections of ground ( or the levee ). Most of the trees on all the levees around the city have since been removed.
Mystery Breach: Location C
Drive on Marconi Dr. to get to this final location, you can not access it from the freeway. In most places around the city, the drainage canals that flow directly into Lake Pontchartrain have an I-wall on top on them. This I-Wall provides an additional 3 to 6 feet of flood protection to the City. Notice what the I-wall does here at this location. The water was a couple of feet over the top of the dirt levee where it breached in the 17’th street Canal. The I-wall kept most of the water over the dirt levee out of the city (except where it breached). The water was also several inches to a foot over the top of the dirt levee here on the Orleans canal (our Mystery breach). Can you come to any reasonable conclusion as to why the flood protection wall does this? It is amazing, but this was designed this way on purpose. Since the I-wall here was designed to do this it is not an "official" topping or breach. Can you say D’oh!
Sources:
I obtained most of the following information from a field trip that Dr. Stephen Nelson from the University of Tulane put together. He produced a terrific Field trip guide (www.tulane.edu/~sanelson/Katrina/Hurricane Katrina Field Trip 11-12-06.pdf). I would recommend reading if you are interested in the levees and how they failed.
I also received some of this information from ILIT or the Independent Levee Investigation Team Final Report 2006. You can download their entire report from the LSU Law School (https://biotech.law.lsu.edu/katrina/ILIT/index.html). This is a detailed in-depth study of what went wrong and what can be done about it.
To log this Earth Cache:
To get credit for this cache, you must do the following. Please send me the answer to the question about location C, do not post in your find.
1. Location A: Take your picture by the 17’th street levee breach. They demolished the houses in front of the repaired levee and installed a memorial. Post your picture on-line when you record your find.
2. Location C: Mystery Levee Breach on the Orleans Canal. Take a look at the I-wall on top of the levee. What happens to the I-wall designed to keep the water out of the city in case of a large flood? Where did the water go? Why do you think they designed the wall like this?
Continued in New Orleans Levee Breaches Part II
I hope you learned something along the way.
Help thy Neighbor during times of trouble.
Take care, and keep on caching,
Oilman w/ Fuzzylogic.