Compare Isle de Jean Charles to a Nearby Community

Reduction of storm surge by protective landscape features

First, let's consider how protective natural landscape features (barrier Islands, marshes, ridges of high ground, etc.) can reduce (or attenuate) the storm surge by offering friction and reducing the energy of the water. The actual rate at which this happens varies according to many variables, including the dimensions of the barrier island, the health or level of degradation of the marsh, the height of the levee, etc. It is hard to quantify this so we will use an arbitrary (estimated) number for now. We will say every 1 km of marsh land reduces the surge by 10 cm.

If there is a 10 m storm surge at Timbalier Island and the distance from Timbalier Island to Isle de Jean Charles is ~35 km, what will the height of the storm surge be at Isle de Jean Charles?

Would the 2 meter high levee protect Isle de Jean Charles from such a storm surge?

Enter your answers in the Module 8 Lab .

Storm surge effects

A storm surge of just 3 meters can do considerable damage. The energy of the water, combined with the wind can move large objects and flood any houses that are not raised above this level. Higher storm surges of course do even more damage. The residents of Isle de Jean Charles receive frequent flooding from storm surges. Many surges that reach the community are less than 1 meter so the small levee protects them. But what if a Category 4 storm hit the Louisiana coast directly south of Isle de Jean Charles, delivering a 10 meter storm surge at Timbalier Island? If the barrier islands and marshes reduce the storm surge by 4 meters and the town receives 6 m of water, what effects would the residents experience?

You don't need to submit your answer, but take some time to think about what 6 meters of water would do to a town that's only 1 meter above sea level to begin with.

Compare Isle de Jean Charles to a nearby community to be protected by the "Morganza to the Gulf" hurricane protection levee

Readings

• Revisit the fact sheet on the Morganza to the Gulf Levee project.
• Also, read the Times Picayune Article from May 2013

Examine the maps in these links and locate the towns of Montegut, Chauvin, and Dulac. These communities are at a similar distance from the Gulf as is Isle de Jean Charles, but they will be within the footprint of the Morganza to the Gulf Levee. As the Times Picayune article states, the elevation of the levee will be between 10.5 and 24 feet (3.2 – 7.3 meters). This is an average of about 5 meters. We will use this number in our calculations.

• Navigate to Dulac, LA (29˚23'20" N; 90˚42'50" W) using Google Earth.
• Measure the distance from Dulac directly south to Trinity Island (29˚03'05" N; 90˚43'05" W).

Record the distance in the Module 8 Lab .

• Using the hypothetical storm surge of 10 m at landfall (Trinity Island) and the estimated surge reduction factor used previously (1 km of land reduces the surge height by 10 cm), calculate the height of the storm surge be when it reaches Dulac.
• Would the 5-meter high "Morganza to the Gulf" levee protect Dulac in this case?
• What level of storm surge, as measured at Trinity Island (landfall) will Dulac be protected from once the levee is built?

Enter your answers in the Module 8 Lab .

Disclaimer

This is just an estimate for the purposes of understanding the challenges faced by those living in these coastal communities. We cannot quantify exactly how the various landscape features protect now and in the future, sea level rise and further erosion of barrier islands and marshes must be factored in to any calculations.

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Figure 8.11: Raised House, Isle de Jean Charles.
Credit: Gary Allen