Where Does All the Water Go? - Activity - www.TeachEngineering.org

Hands-on Activity: Where Does All the Water Go?
Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Colorado: Math
- b. Solve multi-step word problems involving fractions, decimals and whole numbers (Grade 6) [2009]
- c. Compute unit rates in real-world situations involving mixtures, concentrations, and distance-time relationships (Grade 6) [2009]
Colorado: Science
- b. Use evidence to model how water is transferred throughout the earth (Grade 6) [2009]
- c. Identify problems, and propose solutions related to water quality, circulation, and distribution - both locally and worldwide (Grade 6) [2009]
International Technology and Engineering Educators Association: Technology
- E. Technologies can be used to repair damage caused by natural disasters and to break down waste from the use of various products and systems. (Grades 6 - 8) [2000]

What happens when it rains? Where does the water go? (Accept student answers.) It either runs over the surface of the earth to a body of surface water — such as a lake, river or stream — or it filtrates down through the ground. Once in the ground, it becomes groundwater. Groundwater flows very slowly through the dirt or soil under the ground to a space called an aquifer.

(Draw the following figure on the white/chalk board.)

A diagram of ground water. Shown are three lines with the top line labeled "Surface." The middle line is labeled "Water Table." Between the top two lines is "Soil" (shaded brown) and "Unsaturated Zone." Between the bottom two lines is "Aquifer" (shaded blue) and "Saturated Zone."

Figure 1. Groundwater diagram

What is soil? Can you think of different types of soil? How would these types of soil affect the water's ability to flow through the soil? (Answer: Soil with larger pore spaces allows greater water flow. For example, water flows through rocks or large pebbles faster than through sand.) We call the spaces between the individual particles of soil, pores or porosity and the ability for the water to flow through the soil as permeability.

Environmental engineers have developed methods to treat the water in aquifers so that it can be used as a source for drinking water. However, sometimes toxic chemicals that are dumped into the ground seep into our aquifers and make the water harmful to use. Environmental engineers not only figure out how to treat the water for these hazardous chemicals, but they also use groundwater modeling to determine where the chemicals came from and how fast they are moving through the soil. When they model the groundwater flow, they need to figure out the porosity and permeability of the soil, the direction of flow and the velocity of the chemicals. They need to look at these measurements in the areas surrounding a chemical spill, because chemicals spread out in all directions. This is called a chemical plume. Today, we are going to look at a groundwater model and investigate different types of soil. We will also calculate the velocity of a harmful chemical to see how fast it flows through the different soils.

Before the Activity

Obtain a groundwater tank of some sort. If this is not possible, the activity can be replaced with the "What's Down the Well" activity (from Lesson 4 of this unit). Find a groundwater model to use; many schools have one. If yours does not, you could likely borrow one from a local college/university. (Also, it would be a good idea to check with surrounding high schools.)
Make enough copies of the Where Does the Water Go? Worksheet so that each student has their own copy.

With the Students

Write the following terms on the board and ask students to think about what they mean: water table, groundwater, aquifer and soil.
Demonstrate groundwater flow using a groundwater model tank. It is best to have different types of soil — one coarser grained like gravel and a finer grain soil (like sand) — and include an example surface water feature (like a lake). Add food coloring to the surface water so students can visualize how the water can flow from the surface water to the ground and then move under the ground.
Ask students how fast they think the water is flowing through the tank. Ask the students to recall anything they know about velocity. Tell them velocity is equal to distance divided by time. Ask students how they could calculate the groundwater velocity.
As a class, have one student measure the length of the tank and one student time how long it takes for die added to one side of the tank to reach the other side of the tank. With these two numbers they should be able to calculate velocity.
If time permits, have the students calculate the velocity through individual types of soils.
In groups of three, have students make a poster of what they saw in the demo. Their posters should include all the different types of soil in the tank and a key that labels and describes the different types of soils. Students should also label and define the following items: water table, aquifer, flow direction.
If time allows, have students present their drawings to the classes.
Have students complete the Where Does the Water Go? Worksheet in class or as homework.