Activity 1: The Everglades Spending Plan - Water Budgets and the Hydrologic Cycle

Purpose
This activity will acquaint students with the hydrologic cycle and introduce watersheds and water budgets. Students will realize that water is a limited resource and that they will have to consider competing interests as they allocate this resources.

Materials

• 1/2-gallon clear plastic beverage bottle,
• roll of masking tape,
• marker,
• water, and
• graduated cylinder or beaker.

Procedure

1. Before beginning the activity, discuss the hydrologic cycle with students. (This information may be for review.) Ask students to make a sketch that explains the hydrologic cycle, then use the illustrations to review the components of the hydrologic cycle. Explain that water circulates continually in its three states - liquid, solid, or vapor - through the geosphere, atmosphere, hydrosphere, cryospohere, lithosphere, and the biosphere.
2. In small groups, have students discuss the meaning(s) of the term, "watershed." Provide dictionaries, encyclopedias, and textbooks. How many definitions can they find? Direct the discussion to the following definition of watershed: all of the land that drains into a particular body of water.
3. Have students brainstorm about the possible sources of water and various methods of drainage, such as rivers, streams, rainfall runoff, storm drains, gutters, and so forth. Have students generate a list of ways that humans affect the watershed system. Revisit this topic as you introduce Activity 2, "How Big is the Watershed?"
4. Working in pairs, have students calibrate a clear plastic bottle in 50 mL graduations by placing a strip of masking tape along its length and marking the gradations. Have them pour 50 mL of water into the bottle and mark the water level, continuing this process until the bottle is full.
5. Tell students that the water in the bottle represents the amount of water in a model watershed, and that they are in charge of allocating water for a growing town of 1,000 households. Before the students begin allocating, have them make a list of uses for the water in the model watershed. (Use the following table as a guide.) Point out that there is a minimum volume of water required to sustain streamflow and that streamflow must be maintained. You may wish to assign mL of water use per household for each water use, or you may use the sample provided below.
6. Once the amount of water used for each purpose has been assigned, have the groups pour water from their 1/2-gallon bottles to represent each use for the 1,000 households in the town. Students should record the amount of water left after each withdrawal.
7. Have students devise a method to determine the maximum number of households the model watershed can support.
8. Once the activity is complete, lead students into a discussion of water budgets. (Use the information below as background for the discussion.) Ask them to revisit the Focus Question for the Everglades. How will the drought affect the water budget in general? What effects might the drought have on each of the interested parties?

Discussion of water budgets
When discussing the concept of a water budget (the freshwater available for plant, animal, and human use plus the water necessary to maintain stream flow), you many want to begin by discussing the distribution of water in the hydrosphere:

97.30% in the ocean (saltwater),

2.14% frozen into glaciers,

0.54% ground water,

0.02% in streams, rivers, freshwater and saltwater lakes, and soil moisture.

To determine a region's water budget, hydrologists consider "deposits" to be water from precipitation, and "withdrawals" to include water lost to the atmosphere through evaporation and transpiration, water which runs off to rivers, streams, and lakes, and water that seeps underground. Humans also make withdrawals from the water account. Although much of this water is recycled back into the system, only a small portion of water used in agriculture is returned to the account. When the account is overdrawn, humans rely on water supplies stored in aquifers.

For the continental U.S., about 3.8 trillion gallons of water are credited to the water account annually through precipitation. Sixty-six percent is returned to the atmosphere through evapotranspiration, 31percent runs off and 3 percent enters the ground-water supply. South Florida's water budget differs from the national water budget. To highlight south Florida's unique water budget, refer students to the inflow and outflow pie charts in their Student Packets.

Adapted from "Watershed Wisdom." Ellen Pletcher Metzger, Journal of Geological Education, 1993, v.41, p. 508.