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Hydrosphere: Questions and Answers

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Detailed Example of Using Socratic Questioning in Class
Content Area: Hydrosphere

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This sample of plausible questions and responses is designed to help guide the instructor through an entire Socratic lesson. Specifically, it will help instructors learn how to create Socratic questions and design a session of Socratic questioning. It begins with a general question about the hydrosphere, then explores components of the hydrosphere, and finally moves to the specific case of a change in surface material/land cover at Earth's surface.

The instructor/teacher is identified as T, and the student as S. Some of the questions below are identified in terms of the type of question, as follows:

T. Imagine that it has been raining for 2 days in an area on the outskirts of Denver, Colorado, during July. Total rainfall for the event is 2 inches. The nearly level terrain is covered with wheat fields. What happens to the rain? (I&C)

[It helps to show an image at the same time. An image of a wheat field in Colorado is provided with this module. Wait at least one minute to give students time to reflect, then call for students to raise their hands if they have an answer. If not, choose and call on someone at random.]

S. It soaks into the ground.

T. What are you assuming if you say that 2 inches of rain soaks into a wheat field? (A)

S. That the ground is permeable.

T. Okay, if you are assuming that the ground is permeable, would all 2 inches soak into the ground, even if it is permeable?

[Note: It sometimes helps for the professor to restate as closely as possible the students answer, to give the rest of the class time to hear and think about the response. In this case, the teacher has restated the answer within the next question.]

S. Yes.

[The purpose of this wrong answer is to help the instructor see how to draw information from a student who seems not to know the answer.]

T. Think about your answer for a moment. Everyone in the class think about the following question: Is there any process you can think of that would return some of the rain water to the atmosphere before it soaks into the ground? (C)

[Students sit quietly. No one raises a hand.]

T. Okay, what happens if you set a bowl of water on a picnic table and let it sit outside for several hours on a warm, sunny afternoon? (I&C)

[Call on any student who raises his or her hand.]

S. It evaporates.

[Return to the student who had the wrong answer, saying that all 2 inches would infiltrate the ground.]

T. Okay, do you think that any of the 2 inches of rainfall would evaporate before it soaks into the ground? (I&C)

S. I guess it must.

T. Yes, it does. In the Denver area, the average rainfall each year is 12 inches. Look at the annual rainfall map for the U. S., and you can see that this is much lower than in the central or eastern U.S. The average annual rainfall for a given area is shown as a range from low to high, with boundaries representing the low and high values. Now look at a similar map that shows the annual amount of evapotranspiration for the U.S. What is the annual amount of potential evapotranspiration for Denver? (C)

S. It looks like the potential evapotranspiration is 24 to 36 inches each year.

[Here the instructor might need to pause to describe the potential evapotranspiration map in order to make sure that all students see how to interpret the diagram. Discuss the colored areas and ranges of values that each represents.]

T. We should stop for a moment to discuss the various terms and processes that we've identified so far, then we'll come back to this concept of potential evapotranspiration. We've talked about rainfall, infiltration, evaporation, and evapotranspiration. Let's put definitions for each word on the board and briefly discuss the differences. [The list of definitions could be done as a series of clarification questions, such as "How would you define infiltration?"]

Definitions:

Rainfall
The amount of water falling over a given area over a given time.
Infiltration
The gradual filtering or passing of water through porous geologic materials (e.g., soil, unconsolidated sediment, or fractured rock) at and near the Earth's surface.
Evaporation
The transformation of a liquid (water in this case) to a vapor (water vapor).
Evapotranspiration
The return of water to the atmosphere through evaporation from Earth's surface and the escape of water vapor from plant leaves.
Transpiration
The transfer of water vapor from plant leaves to the atmosphere by evaporation.

T. What is similar about each of these words? ((I&C)

S. Each one involves the transfer of water from one place to another.

T. Yes, each one is a process that moves water from one reservoir to another. Each reservoir stores water in some fashion. Reservoirs for water include the atmosphere, the unsaturated porous ground, and the saturated groundwater system. The continuous cycling of water from one reservoir to another has a name. What is it?

S. The hydrologic cycle.

T. Let's go back to the maps of annual rainfall and potential evapotranspiration. For Denver, average annual rainfall is only 12 inches, but the potential for evapotranspiration is 2 to 3 times as much, some 24 to 36 inches per year. Because the rainfall is less than the potential for evapotranspiration, most or all rainfall will return to the atmosphere. Depending on weather conditions, however, at some times some rain will infiltrate the ground rather than be evapotranspired. What happens to this water? (C)

S. It keeps going down until it hits the groundwater.

T. Yes, it could travel down to the groundwater table, but what if the ground was already wet and saturated, as after a day of heavy rainfall. What might happen to that water? (I&C)

S. It would have to run off the ground.

T. Yes, surface water runoff is yet another transfer process within the hydrologic cycle. Where would that water eventually end up if it kept running down a sloping surface? (I&C)

S. In a stream.

T. Have you ever noticed that sometimes you can see water in a stream even if it hasn't rained and there hasn't been any surface water runoff for for a long time. Where does that water come from?

S. Water in the ground can seep into the stream, like from a spring.

T. Yes. Now we've identified all of the main parts of the hydrologic cycle. Each one of you now can summarize the hydrologic cycle with all of its reservoirs and flows, or transfers, of water from one reservoir to another. In your summary, list each reservoir and each transfer process. Go ahead and write the two lists on paper, then I'll call on one of you to call out your lists.

[At this point, give the students 2-3 minutes, then call on someone and write their lists on the board. If a student's list is incomplete, help him or her determine missing elements via additional questioning, or call on someone else to contribute if that student seems too stumped.]

T. If we're standing along a stream before it rains, and we see water flowing in the stream, it's likely to have come from the groundwater reservoir, or perhaps snow melt from upstream depending on weather conditions, time of year, and so forth. If it's from the groundwater reservoir, it is called baseflow. If rainfall then occurs, and if some water runs off the slopes rather than evapotranspires or infiltrates, then the water in the stream will begin to rise. This contribution to streamflow is called stormflow. We can illustrate the two components in a hydrograph, as shown in this figure. [Show a hydrograph figure for pre-urbanized/suburbanized conditions. A sample that shows both before and after conditions is included with this module under Teaching Materials.] The vertical y-axis on a hydrograph represents the amount of water (by volume) in a stream for a given unit of time. This is called discharge. The horizontal x-axis represents time. What do you think would happen to this hydrograph if it represents a stream along the base of a long slope of wheat fields that are converted to a new housing development with paved driveways, slate roofs, and grassy lawns? Can you sketch a new hydrograph over the old one to show such changes?

[Give students time to sketch the original hydrograph for the wheat field condition, or present it to students as a handout. Allow them 3-5 minutes to sketch a new hydrograph over the old one for the case of a new housing development and altered runoff conditions. In our experience, this is a challenge for many students. A sample picture of a new suburb could be shown for this example. Walk about to look at their sketches as they develop, and as a number of them complete their sketches return to the front of the room to call on someone to discuss their answer.]

T. Okay, you've had time to sketch a hydrograph that represents new conditions in the hydrologic cycle. What are the main differences between the original and the post-development hydrographs? (I&C)

S. There will be less infiltration and more runoff.

T. If there is less infiltration and more runoff, what happens to baseflow and stormflow? (I&C)

S. There should be less baseflow, because less water goes into the groundwater reservoir. There would be more stormflow.

T. Yes, and if there is more stormflow, that means that flooding is worsened. How could land-use managers design new developments so that groundwater recharge still occurs and so that flooding is not exacerbated? (I&C)

[At this point, the instructor can guide the students to an understanding of how retention basins are used to hold water for sufficient time to maintain a hydrograph that resembles the pre-development hydrograph.]


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