Most children have had some experience with land and water. For example, a child plays on a sandy beach or runs along the banks of a stream. Another marvels at the variety of clouds or creates mud pies after a gentle rain. Whenever children play outdoors and explore the environment, they have informal experiences with some of the concepts included in Land and Water.

In this unit, students investigate the interactions between land and water. Using a stream table as a model, they create hills, build dams, and grow vegetation. Miniature valleys, waterfalls, and canyons form in the stream table as water flows over and through the soil. From these firsthand observations, students discover how water changes the shape of land and how features in the land, in turn, affect the flow of water.

By the time they reach fourth grade, students can analyze cause and effect. They are ready to grasp the effects of flowing water over and through land and the effects of various land features on the flow of water. The first of these two concepts is covered in Lessons 1 though 10; the second in Lessons 11 through 16. Each lesson of the unit builds on the previous one; by the end, students have both a practical and an intuitive understanding of some of the complex interactions between land and water.

Lesson 1 challenges students to think about land and water and gives them an opportunity to generate questions. As students examine photographs of particular changes in the land caused by flowing water, they begin thinking about interactions between land and water in their own world. This lesson serves as a pre-unit assessment and is matched to corresponding activities at the end of the unit.

In Lesson 2, students build a land model by mixing four soil components in a clear plastic box and creating a lake at the base of the land. They use the land models to simulate the water cycle. They observe how water changes its physical form. A reading selection on how people "tap into" the water cycle concludes the lesson.

In Lesson 3, students use a sprinkler head to model the effects of rain on land. In Lesson 4, students use their land models from Lesson 2 in a new way--as a stream table. They attach a cup with a hole to one end of the box and pour water through the cup and onto the soil. Students observe a narrow stream channel forming in the soil and investigate how flowing water changes the shape of the land. They also collect runoff so they can compare the amount of sediment carried by water in this lesson with the runoff produced by various stream table setups throughout the unit.

In Lessons 5 and 6, students take a closer look at four soil components in their stream tables. They examine the properties of each component, both dry and when added to water, and observe where the water goes when it falls on each of the soil components. By examining water flowing into and off each soil component, students grasp the concepts of ground water and runoff. Through a reading selection, they learn where drinking water comes from.

As students test the speed of a stream in Lesson 7, they observe how terrain affects the velocity of the stream and how velocity affects the way in which water erodes and deposits soil. Through a reading selection on glaciers, students gain more information about how water in its solid form--ice--can affect land.

Lesson 8 introduces aerial drawing. By drawing their results from a "bird's-eye view," students find they can examine the entire stream system. They also establish a common vocabulary for the various parts of a stream.

In Lessons 9 through 14, students conduct additional stream table investigations. By modifying their stream table setups in various ways, they examine how water and land interact under different conditions. For example, students use a stream source cup with three holes to create multiple streams and a cup with one large hole to model an increase in stream flow. They also add hills and rocks to their landscapes, construct dams, elevate one end of their stream tables to model the effects of slope on water flow, and add plants to their stream tables to control erosion. At the conclusion of Lesson 9, students complete a self-assessment that helps them determine their progress thus far in the unit. In addition, a reading selection on dams in Lesson 12 encourages students to think about the advantages and disadvantages of dams for controlling the flow of water.

The final two lessons serve as an embedded assessment that challenges students to design their own landscapes, predict how their land will be affected by runoff, propose optimal homesites in their landscapes, test their predictions, and evaluate their homesites. These final lessons provide information you can use to assess student growth in the concepts and skills of the unit. The unit closes with a reading selection about a unique home, Frank Lloyd Wright's Fallingwater, built over a stream.

Following Lesson 16 is a post-unit assessment that is matched to the pre-unit assessment in Lesson 1. The additional assessments provide further questions and challenges for evaluating student progress, and they allow students to apply information learned in the unit to their own world.

This is a rich unit for students. They learn to use models to study the interactions of land and water and to test these interactions under various conditions. They are challenged to make comparisons on the basis of their own results and those of their classmates. They relate their models to the real world as they apply learned concepts to photographs of land and water on earth. Through these applications, students will be encouraged to observe land and water each day and to search for evidence of land and water interactions in the world around them.