Investigating Influence of Wind Speed and Slope on Storm Surge

Storm Surge and Isle de Jean Charles

Using your calculated bed slope number for Isle de Jean Charles, experiment to find out how wind velocity values affect the storm surge level. The water depth will stay at 10 m. The slope will stay at the calculated value. Just manipulate wind speed and enter the values in the chart below.

Tip: To "visualize" the wind speeds in more familiar units of miles/hour (mph) – roughly double the m/s value, so 20 m/s = 44.74 mph; 60 m/s = 134 mph) A hurricane with wind speed of 130 - 156 mph is a category 4, according to the Saffir-Simpson Scale.

(Note: the model may not allow you to put in exact values – so use the closest value it will allow)

Enter the numbers into your worksheet.

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Figure 8.10: Screenshot of the surge model.

Credit: CoastalHazards.org

Reduction of Storm Surge by protective landscape features

The effect of "lines of defense" (barrier Islands, marshes, ridges of high ground, levees, etc.) is of course to 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.

So if there is a 10 m storm surge at Timbalier Island and the distance from Timbalier Island to Isle de Jean Charles is 35.5 km, what will the storm surge be at Isle de Jean Charles?

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Visualizing 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.

Reflection question:

What if a Category 4 storm hits 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?

Write your reflection in your worksheet.