COASTAL FLOODING DURING HURRICANES: During a hurricane, the drop in air pressure

Question

COASTAL FLOODING DURING HURRICANES:

During a hurricane, the drop in air pressure that occurs, combined with air flow toward the center of the storm, causes the sea surface to rise. In intense storms, it can rise 20 feet, and in some cases, it has risen as much as 40 feet. Because much of the land adjacent to the Gulf coast is so flat, the rise in sea level associated with storm surges inundates much of the land along the coast, and this is one of the reasons storm surges are so hazardous. In addition, the storm waves that are generated on top of the storm surge also case damage – both because of the added height of the water level and because of the force of impact of the waves.

During a hurricane in 1969, a woman who lived in an apartment building across the street from the beach decided to throw a ‘hurricane party’. So she invited guests to come over and ride out the storm in the resumed safety of their concrete and brick apartment building. What this woman and her guests did not know about, or did not fully appreciate, was the rise in sea level associated with storm surges during hurricanes and the force with which the waves can strike shore. A cubic foot of water weighs 55.6 pounds and, during a storm, the waves can reach speeds of up to 55 mph.

To illustrate what this means, calculate the weight of a wave striking the building based on the assumption that the wave struck the entire front of the building and that the building was 30 feet tall and 70 feet wide. In this problem we’ll make the simplifying assumption that the part of the wave that struck the building was a ‘wall’ of water 30 feet high, 70 feet wide, and 3 feet thick from top to bottom. (Obviously waves are thicker at the bottom than at the top, but we’re ignoring this to make the calculation easier.) To determine the weight of the wave, determine the volume of the wave (in cubic feet), and then multiply the volume by 55.6 pounds per cubic foot.

Volume = height x width x thickness = ___________________ft3

Weight = volume x 55.6 lbs/ft3 = ____________________________lbs.

This large number represents the weight of only one wave. Hundreds of waves would have hit the building during the course of the storm. Based on this calculation, it is easy to see why the apartment building was completely destroyed; nothing was left but the foundation. Tragically, the only person to survive the party was the lady who gave it – her 20+ guests were killed.

What was the moral of this story if you live along a beach and a hurricane is approaching?

Explanation / Answer

Volume of the wave= height* width* height

=30*70*3=6300ft3

Weight=volume*55.6lbs/ft3=6300*55.6=350,280lbs/ft3

Since the 6300ft3 is the volume of one wave only and weight of the one wave which impact the building is 350,280 ft3. There are hundreds of such waves which struck the building so this is why the building is completely destroyed.

The moral of the story is that we should not never underestimate the power of natural forces like hurricane, earthquake. Since these natural forces operate on a very large scale and are very powerful and have the ability to change the configuration of landforms. The speed of hurricane ranges from 74-156mph. So If we live on a beach and we receive the warning of approaching hurricane we must the evacuate the place as soon as possible and move to some safe place away from the beach.

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