Credit: Susan Hurstcalderone, science and resource teacher, Blessed Sacrament School, Washington, D.C.
Length of Lesson:
Two class periods
Students will understand the following:
- Different types of soil have different capacities for retaining rainwater.
- If the soil in an area will not hold enough rainwater, flooding problems will ensue.
- Soil can be tested for its water-retaining capacity.
The following materials should be distributed to each group:
- Three soil samples: sand, agricultural soil (potting soil), and clay
- Three measuring cups
- Filter paper
- Present the following scenario to your students. The class is a team of "consulting engineers" for a new housing development to be built in the next county. Many of the county's citizens are protesting the development. They are saying that the soil in that area will not hold the rain and there will be flooding problems for all dwellings in that area. But others believe this is just an excuse to delay and block the development.
- Tell students that their challenge is to aid in the decision-making process by testing different samples of soil to see how much water the soil will absorb.
- Divide your class into small groups, distributing materials to each group.
- Students should first test each type of soil in its dry state by measuring the same amount of each soil, in turn, into a funnel lined with filter paper, and then pouring a measured amount of water through it. They should use the same amount of water for each type of soil. The water that drains through each type of soil should be collected in another measuring cup and the amount recorded.
- Have students repeat the test using the same types of soil in their saturated states.
- Discuss with the class which soil held the most water when dry and which saturated soil held the most water. Which type of soil would be most likely to cause flooding problems?
- Have each student write a lab report describing the soil tests, including an explanation of how communities and developers would use such tests.
Adaptations for Older Students:
Have students find documentation for soil testing that has been done in their own community and report their findings to the class.
- Explain why a river can flood even if there was no recent rain in that section of the river valley?
- Why are sediments found in rivers? Discuss how rivers carry sediments and explain how this impacts the land during a flood.
- What characteristics determine how much water soil can hold?
- Debate the merits of building dams upstream to prevent flooding-thereby making former floodplains available for development.
- Discuss why hydrologists-scientists who study the water cycle-track snow accumulation as a part of long-term flood forecasting. What other data would help them make more accurate flood predictions?
- Debate whether or not people should be allowed to rebuild homes in an area prone to serious flooding.
You can evaluate your students on their lab reports using the following three-point rubric:
Three points: accurate and complete description of each soil test; clear explanation of how tests would be used; careful and error-free writing
Two points: satisfactory description of each soil test; explanation of how tests would be used lacking in clarity; some writing errors
One point: sketchy description; unclear explanation or no explanation; numerous writing errors
You can ask your students to contribute to the assessment rubric by determining what information should be included in the description of each soil test.
Cities and Floods
Have students use either a map of the United States or a large local map to locate and label major rivers on the map. Students can then label major cities near the rivers. Divide the class into groups to research a particular city and the river associated with it. The research students gather should include historical, geographical, geological, and meteorological information on their river and city. Information could include the following: when the city was founded, what industries make particular use of the river, what the elevation of the city is, where the town cemetery was built, what year and season the last flood occurred, how high the river has risen, and whether the city has taken precautions against future floods.
Measure Flood Velocity
Use a stream table to explore with your students the impact of slope on water velocity. (If you don't have a stream table, a long rectangular planter, wallpaper trough, or piece of gutter will also work.) Arrange your equipment so that students can vary the height of the container and thereby change the slope. Fill the container with sand, potting soil, or clay. Using a measured amount of water and a watch with a second hand, students can determine the velocity of the flow based on the height (slope) and length of the container. With each change in the slope of the container, have students draw the erosion patterns. Students can display their results in a graph and discuss ways that communities use this type of data. For example, they might observe the edges of a highway from a safe location and then, back in class, discuss how engineers have designed highways to be protected from high-velocity running water. How is erosion prevented?
Michael Allaby. Facts on File, 1998.
This work discusses floods, from basic meteorology to floods caused by tsunamis. It also discusses man's attempts to prevent and control flooding.
"Tearing at the Earth"
Craig Childs. Audubon, May-June 1998.
In the desert, flash foods strike quickly and powerfully. In the process, they move boulders and carve stone.
FEMA: Fact Sheet: Floods and Flash Floods
Information on floods, maps, and mitigation.
The Weather Channel-Project Safeside: Flood and Flash Flood Safety
Information and photographs of floods.
Flood Warning Home Page
Good graphics and maps on rainfall data of the United States.
The Hydrologic Information Center
Lots of information including rivers, floods, historical records, the national water supply and current conditions.
An embankment for preventing flooding.
Context: Eventually, rivers break through their banks and levees.
In India and adjacent areas, the season of the southwest monsoon (a wind in the Indian Ocean) characterized by very heavy rainfall.
Context: The timetable of life is driven by the arrival and departure of the monsoon. The monsoon's path is ultimately blocked by the mighty peaks of the Himalayas.
The entire tract of country drained by a river and its tributaries.
Context: A belt of violent storms traveled right along the line of the river. All the water they produced was caught in the same river basin.
Loose sedimentary material with rock particles usually 1/20 millimeter or less in diameter.
Context: Before they could begin to estimate the flood damage, hundreds of tons of silt had to be removed; it had all been washed off the mountain slopes by the torrential rain.
Saturated with water.
Context: The land was so waterlogged by heavy rain, the soil could no longer absorb it and the floods began to build.
Copyright 2001 Discovery.com.
Teachers may reproduce copies of these materials for classroom use only.