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Storm That Drowned a City

Classroom Activity

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Activity Summary
Students will watch a teacher demonstration modeling how wetlands can help reduce a hurricane's impact and describe what the model represents.

Learning Objectives
Students will be able to:

  • record data related to how different meshed materials affect a steam plume.

  • compare results and rate meshed materials according to how much steam each material blocked.

  • infer how wetlands can sometimes help protect land from hurricanes.

Materials for teacher
  • steam kettle with spout
  • hot plate or equivalent heat source
  • protective gloves, such as oven mitts or rubber gloves
  • materials with different mesh size, such as coarse window screening, fine window screening, cheesecloth, facial tissue, paper towel, cotton cloth (e.g., T-shirt), flannel, and diaper
  • solid barrier, such as a block of wood, sheet of cardboard, or spatula
Materials for each team
  • copy of the "Wetlands and Hurricanes" student handout ( HTML)

Background
Hurricanes need two basic ingredients to begin: a source of energy (warm tropical ocean waters) and a disturbance in the atmosphere (such as a thunderstorm). Most Atlantic hurricanes start as storm systems off the coast of West Africa. These storms move westward over warm, tropical ocean waters. A hurricane forms when warm, moist air rises from the ocean surface and begins to condense into storm clouds and rain. As the water condenses it releases heat, which warms the air around it. This warm air begins to rise; as it does so it is replaced by more warm, moist air from the ocean below. This cycle starts the hurricane's spinning motion. As a hurricane travels over the warm water it can gain more energy and increase in strength (a hurricane starts as a tropical depression before developing into a tropical storm and then a hurricane). A hurricane's strength diminishes as it moves over land and is robbed of its warm water energy source. Dense wetlands can help weaken a hurricane by breaking the connection between the hurricane and warm ocean water. Wetlands can also act as a physical barrier, slowing and reducing the force of the waves that reach the shore.

Before Hurricane Katrina hit in 2005, the rate of loss of wetlands along Louisiana's coast had been about 75 square kilometers per year, a loss that had been occurring for several decades. Some of this was due to natural processes such as tides and storm surges. Other losses resulted from dredging canals for sources of oil and the use of heavy commercial and recreational boat traffic through the wetlands. In addition, the construction of levees and concrete channels to control the Mississippi River starved the coastal marshes of the fresh water and sediment necessary to restore and preserve them.

As a general rule, about a kilometer and a half of marsh can reduce a coastal storm surge by about 30 centimeters. The surge that hit the Gulf Coast when Katrina hit was close to nine meters—the highest ever recorded. The surge in Lake Pontchartrain was about three meters. Some scientists believe that a few kilometers of marsh could have lessoned Katrina's impact on Louisiana's coast.

In this activity, students examine how wetlands can deprive a hurricane of some of the warm, moist air that supplies its energy. The steam represents the hurricane and different types of meshed materials represent dense and sparse wetlands. Students will record what happens to the plume of steam (hurricane) when different materials are placed in its path.


Key Terms

hurricane: Intense rotating oceanic weather system with winds of at least 119 kilometers an hour.

wetlands: Lands that saturate with water. Wetlands vary greatly, and are found on every continent except Antarctica.


Procedure
  1. Have students locate the tropical zone south of the equator on a map (the regions between 5° and 20° north and south of the equator are the belts where hurricanes can form). Review with students how hurricanes develop.

  2. Choose the materials you would like to use. Make sure you use at least three materials of different mesh densities (see Activity Answer on page 5 for sample results.) Organize students into teams. Distribute copies of the "Wetlands and Hurricanes" handout to each student.

  3. Boil the water in the kettle. (You can make the steam more apparent by placing the kettle against a dark background.) Safety note: Steam scalds! Wear protective gloves. When placing materials over the spout tip of the kettle, as instructed below, hold the materials so your hands are below the spout tip. Stretch the materials taut over the spout's opening so steam goes through the materials instead of being channeled out to the sides where it can scald your hands.

  4. As the water heats, tell students that the water in the kettle represents the ocean, the hot plate represents the heat from Earth's tropical zone that warms ocean water, and the steam plume represents a hurricane.

  5. Ask students to record their observations about the plume of steam.

  6. Ask students to predict how the different materials will affect the plume when you place them in its path. Have them record their predictions and reasoning.

  7. Put on the protective gloves and place one of the materials across the tip of the spout. Have the class observe and record the effects on the plume of steam. Repeat the demonstration using the remaining materials. Explore how students' predictions compare to what actually happened.

  8. Have each student answer the questions on his or her handout. Work with students to find answers to any additional questions they may have about wetlands.

  9. As an extension, have students research where the nearest wetland area is to their school. Consider with students different types of wetlands such as swamps, marshes, and bogs, and have students find on a local map the wetlands (and their size) that are closest to their school. Have them estimate the size of the wetlands and find during which months the wetlands are most likely saturated with water. Ask students to research the dominant soil type(s) and the names of some of the plants and animals that inhabit the wetland.


Activity Answer

Just as wetlands interfere with a hurricane's supply of warm, moist air, the materials placed over the kettle spout disrupt the connection between the warm, moist air produced inside the kettle and the plume of steam at the spout. The class should see that the plume's strength diminishes as the mesh gets finer.

Effect of Different Materials on a Steam Plume

Material

Effect on the Steam Plume

Coarse window screen

no change in plume's shape or speed at which steam comes out of spout

Fine window screen

no change in plume's shape or speed at which steam comes out of spout

Cheesecloth

speed of steam coming out of spout slows slightly

Facial tissue/Paper towel/ Cotton cloth (T-shirt)

speed of steam coming out of spout slows a little; steam rises straight up rather than leaving the spout forcefully at an angle

Flannel

speed of steam coming out of spout slows considerably; steam cloud becomes just a series of wisps

Diaper

steam cloud significantly disrupted


Student Handout Questions

  1. What kind of wetlands do the coarse-meshed materials represent? The course-meshed materials represent sparse wetlands.

  2. What kind of wetlands do the fine-meshed materials represent? The fine-meshed materials represent dense wetlands.

  3. Why did the fine-meshed materials weaken the steam plume? The fine material reduced the supply of warm, moist air from inside the kettle.

  4. How do healthy wetlands help protect a coastal area from hurricanes? Dense wetlands reduce the amount of warm, moist air going into a hurricane.

  5. Hurricanes die out when they travel inland because, when over land, they are no longer supplied with the warm, energy-rich, moist ocean air. In this kettle hurricane model, what could you do to the model to represent what happens when a hurricane travels inland? Students' suggestions may include interrupting the flow of steam with a solid barrier, such as cardboard, or turning off the hot plate to eliminate the supply of warm, moist air.

  6. What are this model's strengths in representing hurricanes and the effect of wetlands? The model accurately shows one way in which wetlands can reduce the impact of a hurricane.

  7. What are this model's limitations? The model shows neither the complexity of a hurricane system nor the true nature of a wetland area.


Links and Books

Web Sites

NOVA—Storm That Drowned a City
www.pbs.org/nova/orleans
Read an interview with one scientist who predicted the effects of a Katrina-like hurricane, learn about New Orleans' 300-year battle with water, track the hurricane's progression, zoom in on key sites that played a role in the Big Easy's flooding, and map the effect Katrina would have had on your city.

Estuaries.Gov
estuaries.gov/newjersey2.html
Provides a set of classroom activities related to estuaries.

Hurricane Features
www.comet.ucar.edu/nsflab/web/hurricane/311.htm
Describes where and how hurricanes form, the damage they can cause, and how they are rated in intensity.

National Wetlands Inventory
www.nwi.fws.gov
Provides information on the characteristics, extent, and status of the nation's wetlands.

What Is a Hurricane?
www.fema.gov/hazards/hurricanes/whatis.shtm
Provides general facts about hurricanes and links to tracking maps, forecasting information, and dates for Category 4 and Category 5 hurricanes that have occurred this century.


Book

Wetlands
by William Niering. Alfred A. Knopf, 1985.
Includes descriptions of different kinds of wetlands and the plants and animals inhabiting them.


Standards

The "Wetlands and Hurricanes" activity aligns with the following National Science Education Standards (see books.nap.edu/html/nses).

Grades 5-8
Science Standard D

Earth and Space Science
Structure of the Earth system

Science Standard F
Science in Personal and Social Perspectives
Natural hazards



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