|For the Classroom |
The Ogallala Aquifer of the High Plains is approximately the size of California and contains an estimated 4 quadrillion liters (4 with 15 zeros after it) of water.
Water that accumulates beneath the surface of the Earth is called groundwater. Contrary to popular belief, groundwater does not form underground "rivers," but is actually found in the small spaces and cracks between rocks and other material such as sand and gravel. Groundwater supplies about 38 percent of the water used for agriculture in the United States.
Water enters aquifers by soaking down into the ground through a process called "percolation." For water to move in an aquifer, the pores between rock materials and fractures in rock must be connected. The capacity of rock material to transmit water is called "permeability." Water moves through different materials at different rates-faster through gravel, slower through sand, and much slower through clay. Therefore, gravel is more permeable than sand, which is more permeable than clay.
If hazardous waste, chemicals, heavy metals, or oil collect on the surface of the ground, rain or runoff percolating into the soil can carry these substances into the groundwater.
The following activity involves learning how water moves through rock material such as sand, gravel, and clay.
Materials: You will need three clear 16-20-oz plastic soda bottles with holes punched in the bottom (or three clear plastic cups with holes punched in the bottom); equal amounts of gravel, sand, and clay; a magnifying glass; and a graduated cylinder for measuring water.
Procedure: Ask students to predict how water will move through gravel, sand, and clay. Then have students test their hypothesis by placing gravel, sand, and clay in the three soda bottles or plastic cups. The material should fill the containers to a depth of about 8 cm. Have students look closely at each container (a hand-held magnifying glass works well). To demonstrate how groundwater moves through underground rock formations, pour about 120-240 mL of water (or colored water) into each container and discuss the results. Which container emptied the fastest? (the container with the gravel) Which emptied the slowest? (the one with clay) Ask the students how the different materials would influence water movement in natural systems.
Many important energy resources are found in the High Plains. Energy resources are classified as nonrenewable or renewable. Nonrenewable resources take a long time to replace, such as coal, which takes millions of years to form. Renewable resources can be replaced in a much shorter time, such as trees, which can be grown relatively quickly. Some renewable energy resources are perpetual, such as solar energy, wind, and tides.
Have students compile a list of activities they do that require energy. Then ask the class to break up into groups of three or more students, assign several of the activities from the list to each group, and have each group prepare a report answering the following questions:
- What type(s) of energy is used for each activity?
- Where does the energy come from?
- How is the energy delivered from its source?
- What are the environmental consequences?
Once the report is complete, groups should report back to the entire class. Students should take notes on each group's report.
One of the distinguishing characteristics of the High Plains is the endless wind. In some states, wind is being harnessed to generate electricity.
Wind is moving air caused by differences in air pressure. Air moves from areas of greater density (pressure) to areas of lesser density. An area of greater air pressure surrounded by lesser air pressure is called a high. An area of air pressure that is lower than the surrounding area is called a low. Winds blow into a low because the air is less dense there.
In locating sites for a possible wind farm (a collection of windmills used to produce electricity), many factors must be considered: the constancy of the wind, its velocity (speed), the distance to carrier lines, and accessibility.
As with any energy source, wind energy has advantages and disadvantages. It does not cause air pollution and it will never be used up. On the other hand, hundreds or even thousands of wind turbines are necessary to produce significant amounts of energy. This takes up a lot of space, and some people do not like the appearance of so many turbines on the landscape.
In the following activity, students imagine that they are planning a wind farm. To select a site for the wind farm, students construct anemometers to measure wind speed and compare measurements of average wind speeds.
Materials: You will need three plastic cups (about 8 oz), three knitting needles, a large cork, a wooden pole or 1/2"-3/4" dowel, a hammer, a nail 3 cm longer than the cork, two metal washers, and a bright-colored marker.
- Have students use a knitting needle to make two holes on opposite sides of each plastic cup, 3 cm from the top. Push a knitting needle through the holes in each cup, then push the ends of the knitting needles into the sides of the cork. Make sure that the cups are equally spaced around the cork. Push the nail through the center of the cork so the point sticks out of the bottom. Put the washers on the end of the nail, then hammer the nail into the top of the dowel so the cork can spin around freely.
- Have students use the marker to mark a bright spot on the bottom of one cup. This will enable them to count the revolutions.
- Choose a section of the schoolyard, or perhaps a park near the school, where the wind farm will be located. Assign each team about six sites to test for wind speed.
- At each site, the team should set up the anemometer they have constructed and count the number of revolutions per minute caused by the wind. Students should note the exact location of each of the test sites and draw a map.
- Back in the classroom, have the teams compare results and decide on the best site for the wind farm.
Extend the activity with the following discussion ideas:
- Find out from the power company how much electricity the average home uses and how many watts the average wind turbine produces.
- Ask students, "What are the environmental hazards of wind farms?"
- Have students research the question, "Is your state a good place to build wind-powered electrical-generating plants?" Students should be able to explain the criteria used to select a site. Alternatively, you can have students research different states and compare their findings.
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