3. Katrina Case Study
Through a demonstration, students learn about the balance between subsidence and flooding in the formation of a wetland. Students then watch a short 15 minute PBS video about the wetlands ...
Through a demonstration, students learn about the balance between subsidence and flooding in the formation of a wetland. Students then watch a short 15 minute PBS video about the wetlands of Louisiana. They will discover how levee building and the subsequent loss of wetlands contributed to the severity of Hurricane Katrina’s effect on the city of New Orleans. Finally, the class holds a discussion geared towards environmental stewardship and habitat restoration.
Can explain how subsidence and flooding contribute to the maintenance of wetlands.
Can explain how levees prevent flooding and exacerbate subsidence.
Can explain how wetlands protect shoreline from natural disasters such as hurricanes and flooding.
Can discuss the goals of habitat restoration.
Can recognize the importance of environmental stewardship.
3. Katrina Case Study - Logistics
- Computer with internet access, preferably with a projector for the whole class to watch at once, although multiple computers that groups of 4 students can share will also work.
- Watering can to simulate rain
- Pitcher, watering can, or container you can pour muddy water from
- Masking tape
- Clear plastic tray or cup with 3-4 holes punched in the bottom (the clear lids of take-out salad containers are perfect although clear plastic cups will do as well.)
- Square of cheesecloth large enough to cover the bottom of the tray or cup
- Good loamy soil with a mix of sand, silt, clay and organic matter to represent marsh soil (garden soil is fine although you can always collect soil from a marsh to study and observe the real thing)
- Hand trowel
- Large basin that your tray can sit in (a large plastic dishwashing basin works well)
3. Katrina Case Study - Background
The recent hurricane in Louisiana is an ideal opportunity to connect what students are learning about wetlands to real world situations. Students with some background knowledge of what wetlands are and the important environmental roles they play can now apply these concepts to events in the Mississippi River delta.
In their natural state, wetlands are caught in the balance between subsidence and flooding. Subsidence in the most general sense is the sinking of soil relative to sea level. Subsidence is a natural part of wetlands due to soil compaction – air pockets in the soil collapse under the weight of the soil above. In addition, some soil is eroded away by water and wind. Humans contribute to subsidence by extracting oil and natural gas (the soil above collapses when the oil below is removed). Although wetlands are sinking little by little, regular flooding brings in new sediment to rebuild the lost soil and maintain the soil levels in the wetlands. As the plant life in wetlands die, the decaying organic matter also contributes to the overall building of wetland soils. In its natural state, these two forces – soil loss through subsidence and soil building through flooding – are in balance, or in fact, wetlands grow over time as new sediment pours in from rivers and streams.
However, human developments strongly encourage the building of levees, dams, and canals to control flooding and improve water traffic. This prevents the soil building part of the equation, leaving an overall loss of soil year after year. The sediments in the canals shoot out to sea rather than rebuilding wetland soils. Wetlands shrink and eventually disappear. Land sinks. This is why much of New Orleans is below sea level. In fact, many other urbanized delta regions such as the Sacramento River Delta are experiencing the same subsidence problems.
Wetlands provide a natural sponge to soak up flood waters and act as a speed bump, slowing down hurricanes and blocking storm surges. Without much of the wetlands around Louisiana gone and with large areas of developed land below sea level due to subsidence, the effects of Hurricane Katrina were amplified upon the city of New Orleans.
So what can we do? First and foremost, we can educate ourselves and others about the science behind subsidence in order to understand the problem and not make the same mistakes in the future. Secondly, we can protect the few wetlands that remain as stewards of the environment. Finally, we can engage ourselves in rebuilding wetlands through habitat restoration efforts, many of which welcome teachers and their students to participate.
Students should be familiar with what wetlands are and the important functions they serve in an environment. It is helpful if they have played with soil and looked at the components in soil (see Soil Analysis lesson) although it is not essential.
3. Katrina Case Study - Getting Ready
For Subsidence Demonstration
- Make 3-4 hole-punch sized holes in the bottom of the cup or tray.
- Cut a square of cheesecloth to cover the holes.
- Add a 4 inch layer of soil.
- Put the tray inside the larger basin to catch any runoff. Water the soil until water just begins to drip out the holes in the bottom.
- Use the hand trowel to fluff the soil slightly and then smooth the top surface so that it is mostly even.
- Use a piece of masking tape to mark the top of the soil. Match the bottom edge of the tape to the top of the soil.
- Fill the watering can about halfway with water.
- In the pitcher or second watering can, create a mixture of soil and water - approximately 1 cup soil for 2 parts water. Stir.
- Open PBS’s NOW website on the computer you plan to use. Click on “Watch the Video”.
- Preview the video now or pause it to be ready to go when the kids arrive.
3. Katrina Case Study - Lesson Plan
- Quickly review wetlands with the students. What are wetlands? Why are they important?
- Next, tell students that you are going to show them a model of what happens to soil in wetlands over time. Bring out the tray with soil, the watering can and the pitcher of muddy water. Show the students what is in the tray. In particular, point out the level of the soil and the masking tape that marks the surface.
- Explain to students that the soil in wetlands is a mixture of different sized sediments (clay, silt, sand), organic material, and water. In the soil there are air pockets. As soil gets exposed to rain, wind, and animals walking over it, it compacts. At this point, alternately use the hand trowel to pat down the soil in the tray and use the watering can of water to simulate rain. The level of the soil should subside up to an inch.
- Ask the students what they notice. What happened to the level of the soil? Why? Ask students to help define compaction and subsidence given what they observed.
- This process is always happening. Over time, the wetlands would sink completely underwater and disappear. Therefore, subsidence must be balanced by some other constructive force or the wetlands wouldn’t exist. Describe how rivers pick up sediments on their way down from the mountains in the watershed. Stir up the mud in the pitcher. These sediments are carried downstream by the water until they slow down as they pass through the wetlands. Pour some of the muddy water on the soil. Every so often, the river will flood, causing even more sediment to flow out onto the land. Mix up the pitcher thoroughly and pour a large quanity of the muddy water onto the wetlands, allowing a small layer of water to cover the surface and slowly drain out from the drain holes below.
- Again, ask the students what they notice. What happened to the level of the soil? Why? Ensure that students see the balance between subsidence and sedimentation as natural events that contribute to a healthy wetland. Encourage students to predict what would happen if there was more sedimentation than subsidence or what would happen if flooding was prevented altogether.
- Tell students they will watch a video about Hurricane Katrina. If you have time, students may share some of the things they know about the disaster from the media.
- Show the PBS Katrina video.
- Begin a discussion of the video focusing on why there are fewer wetlands and how that increased the severity of the damage caused by Katrina. Some questions you may want to consider include:
- Before the Europeans came to Louisiana, was there more subsidence or more sedimentation? How do you know?
- When New Orleans was first settled, was it above or below sea level?
- Why did settlers build the levees? What effect did this have on the wetlands?
- What else has been built by humans? What impact do these other structures have on the wetlands?
- How much of the original wetlands remain? How quickly are wetlands being lost?
- How do wetlands reduce the impact of hurricanes?
- Allow the discussion of wetlands gradually transform into why wetlands are important and what we can do to save them. Some questions you may want to consider include:
- Did people from the past not care about wetlands? (No, protecting their homes from flooding was more important to them and they didn’t know that wetlands were valuable.)
- Should we care about wetlands loss? Why?
- Do you think our politicians care about wetlands loss? Should they?
- Do you think your parents know about wetlands loss? How can we teach them?
- Should we protect the wetlands that are left? How should we do that?
- Should we try to build new wetlands? Where?
- What does it mean to be a steward of your environment?
- End class on a positive note by brainstorming ways students can help protect, save or restore wetlands.
3. Katrina Case Study - Assessments
- Have students teach a family member about the connection between levee building, wetlands loss, and Hurricane Katrina. Have the family member write a short paragraph about what they learned from the student.
- Ask students to locate a wetland in their local area and find out what plants and animals are there, if they can visit it, and if there are any on-going habitat restoration efforts there.
- National Geographic ran an article in October 2004, 1 year before Katrina, discussing the loss of wetlands in Louisiana and the devastation that would be caused by a large hurricane. Have students read the article and make comparisons between the predictions and what actually happened a year later.
- NOVA and Frontline will air “Storm that Drowned a City” on November 22 at 8 pm. It promises to be an hour long investigation of the science behind Hurricane Katrina, going into far more detail than the 15 minute video highlighted here.
- USGS has a great series of hands-on activities called the Fragile Fringe which provides extensive teacher information and resources on wetlands, their importance and their loss.
- GET INVOLVED! The EPA has an Adopt Your Watershed campaign encouraging kids to become environmental stewards and join forces with the many groups leading cleanup and restoration efforts around the country. To adopt a creek and conduct habitat restoration activities here in the Bay Area, my students and I have worked with:
- Save the Bay
- City of Oakland Public Works Agency
- Urban Creeks Council
3. Katrina Case Study - Sources and Standards
The subsidence demonstration was adapted from the Loss of Wetlands: Subsidence activity from the USGS Fragile Fringe series.
The Audubon Society has a great page on wetlands loss and how to protect what remains.
For additional information, see the Sources and Standards section of the Watersheds and Wetlands activity.
2. Topography is reshaped by the weathering of rock and soil and by the transportation and deposition of sediment. As a basis for understanding this concept:
a. Students know water running downhill is the dominant process in shaping the landscape, including California’s landscape.
b. Students know rivers and streams are dynamic systems that erode, transport sediment, change course, and flood their banks in natural and recurring patterns.
d. Students know earthquakes, volcanic eruptions, landslides, and floods change human and wildlife habitats.