Objective: Students will learn the hydrologic cycle is controlled by natural laws. This lesson provides a basic understanding of the water cycle.

Materials: Water Cycle crossword puzzle, answer key, ice, lamp stand, 40 watt light bulb, 5 lbs plaster of Paris, duct tape, transparent plastic box with lid (about 6"x12"x4"), knife, water, tempera paint (green and brown), brushes, clear acrylic spray, clear plastic bag

Background: The water cycle or hydrologic cycle, is a continuous process in which water is circulated between the earth, plants and animals, and the atmosphere. The total amount of water circulating through the water cycle never changes. However, the form in which the water exists - either gas, liquid, or solid - does change.

When precipitation, such as rain or snow, falls onto the earth's surface, it meets one of several fates. About 85% of precipitation falls directly into the oceans. Some precipitation which falls on land may run across the surface of the soil (runoff) into oceans, lakes, ponds, rivers, and streams. The water that remains at the earth's surface in oceans, rivers and other bodies of water is called surface water. Precipitation may also infiltrate or soak into the soil. This water may be absorbed by plants, or seep down through the soil until it reaches a saturated zone where all the pores between the rock and soil particles are filled with water. Water that reaches this saturated zone is called groundwater. The upper boundary of the groundwater in the soil is called the water table.

Groundwater will eventually reach the earth's surface once again (though it may range from many years to only a few hours) as a spring or seep, by flowing through the soil into a stream or lake, or by being pumped up to the surface. Surface water and water in the soil is warmed by the sun or by being pumped up to the surface. Surface water and water in the soil is warmed by the sun and changes into a gas or vapor. This process is called evaporation. Water in plants may also become vapor through a process known as transpiration. The term evapotranspiration is used to describe the combined process of evaporation of surface water from soil and transpiration from plants.

When water vapor condenses into a liquid or solid and forms clouds, the water cycle starts all over again. It is important to remember that while the form of the water changes, the total amount of water remains the same. This is nature's way of recycling. Imagine, the water you used to wash your face today has been recycled since long before people ever lived on earth.

Procedure:
Distribute the Water Cycle crossword puzzle. Pass out copies of the water cycle picture that is part of The Fountain. Upon completion, have students share responses to the crossword and use the words to introduce the water cycle.

Construct a water cycle model. Raise one end of the plastic box about two inches. Mix plaster of Paris and water to a pancake batter consistency. Pour the mixture into the end of the box that is not elevated. Leave about two inches of the elevated bottom free of plaster of Paris. When the material starts to set up, use your fingers to make hills and valleys. Allow the plaster to dry for at least 12 hours. Paint the landforms after the plaster is hard. Use browns and greens. After paint is dry, spray the landforms with at least two coats of acrylic spray.

Cut a 3" x 3" hole in the plastic lid and tape a piece of clear plastic in the hole as illustrated below. Note: place the lid face down on a piece of cardboard and cut the hole in the lid with a sharp knife.

The model is now ready to operate. Add enough water to form a lake at the low end of the tray. Then place the lamp near the lake. Add ice to the plastic bag and wait for results.

Note: This water cycle box is a very good investment. It really works and can be used over and over again.

Vocabulary Glossary:
Condensation: The change of water from a gas to a liquid
Evaporation: The process of converting or changing into a vapor
Groundwater: Water that infiltrates into the earth and is stored in usable amounts in the soil and rock below the earth's surface
Precipitation: Water droplets or ice particles condensed from atmospheric water vapor and sufficiently massive to fall to the earth's surface, such as rain or snow
Surface runoff: Water (usually originating as precipitation) that flows across surfaces rather than soaking in
Transpiration: Direct transfer of water from the leaves of living plants or the skins of animals into the atmosphere
Water cycle: The cycle of the earth's water supply from the atmosphere to the earth and back which includes precipitation, transpiration, evaporation, runoff, infiltration, and storage in water bodies and groundwater
Grade Level:
4-6

Subject Areas:
Reading, Science

SD Standards for 4th grade:
Reading
4.R.1.1; 4.R.1.2

Science
4.E.1.1; Nature of Science Indicator 2

Setting:
Classroom

Skills:
Inference, Communication, Interpretation, Critical Thinking

Prior Preparation: Collect materials to construct the water cycle model.

Vocabulary:
precipitation, water cycle, evaporation, transpiration, groundwater, surface runoff, condensation
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