Pre-Visit Activities : Groundwater & Runoff : Procedures Sixth - Eighth Grade Online Curriculum : Watersheds

• Clear plastic or glass jars that hold at least a liter (3 per student team)
• Liter measuring beaker
• Liter of marbles
• Liter of clay (clay that is not water-based)
• Liter of sand
• Liter of gravel
• Liter of cobblestones
• Cylindrical funnel
• Nylon netting or pantyhose
• Stopwatch
• Water

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Procedure

Day 1 

1. Introduce this activity by having the students observe what happens to the water that is poured onto the soil of a potted plant. Does it all seep into the soil at once? Does some of it sit on top? What would happen to the water that sits on top if you tilted the plant at an angle? Does it run off? How does this correlate with the rainwater that falls on the ground? Discuss the questions and observations with the students and write their thoughts and ideas on the board. The teacher will use the students’ ideas to introduce the concepts of groundwater and runoff to the students.
   
2. Break up students into small groups. Each group will be given a glass jar with a liter of marbles in it and a measuring beaker. Students will pour 250ml of water into the jar of marbles. The marbles represent soil particles and the water represents rainfall. The students will observe what happens to the water as it falls on the particles, and write their observations down in their journals.
   
3. After the students have done this, ask the class to look at their jar and to consider these questions: Is there part of the volume of the jar where the marbles are completely saturated by water? Do the marbles above this saturated part have any water on them? (Students may want to pick up one of the top marbles to see if it is wet). After discussing these questions with the students introduce the concepts: zone of saturation, zone of aeration and water table. Students will identify these features in their jar of marbles. Students will draw a diagram of their jar of marbles and label each of these zones and the water table. The class will then discuss how this correlates to what is happening with groundwater.
   
4. The students will measure a liter of water in their measuring beaker and pour this into the jar of marbles until the water table reaches the surface of the marbles. By adding the amount of water poured into the marbles to the original 250ml of water that was in the jar they will determine what volume of water it takes to saturate the liter of marbles, and then write this amount down in their journals.
   
5. The teacher will introduce the concept of porosity to the students. Using the amount of water it took to saturate the marbles, the students will calculate the porosity of the marbles. (For example if it took 500ml of water to saturate 1000ml of marbles, the marbles have a porosity of 50%. If it took 275ml of water it has a porosity of 27.5%).
   
6. Students fill 3 beakers, one with 100ml of clay, one with 100ml of sand and one with 100ml of gravel. The clay should be kneaded into the beaker so that no large spaces exist along the edges. Students will predict which of these sediments will be the most porous and which will be the least porous. Students will pour water into each beaker until water saturates the sediment to the top. Students will measure and record the amount of water it takes to saturate each sediment type. Students will calculate the porosity of each (For example, if it takes 40 ml of water to saturate 100 ml of sand, the sand has a porosity of 40%).   
   
7. Students will compare their findings with their predictions. Students will think about these questions: Why did or did not the predictions differ from the actual findings? Does the sediment have uniform sizes and shapes? Which is more like nature, sand or marbles?

8. Introduce and explain the concept of permeability to the students. The students will stretch nylon netting along the bottom of their funnel and wrap it around with a rubber band. The funnel will be filled with 100ml of clay. Clay should be kneaded into the funnel so no large spaces exist along the edges. The funnel will be placed over a graduated beaker. 200 ml of water will be measured. The students will pour the water into the funnel and time how long it takes 100 ml of water to go through the funnel to the beaker below. Students will begin the timer as soon as the water is poured and will stop timing when 100 ml of water flows into the graduated beaker. The students will write the time down.
   
9. Students will fill the funnel with 100 ml of sand and repeat the procedure used with the clay.
   
10. Students will fill the funnel with 100 ml of gravel and repeat the procedure used with the clay.
    
11. The students will compare the different times they recorded to infer how particle size affects permeability.
    
12. The teacher will discuss the particle size difference between clays and sands. The teacher will explain that clays and sands are the predominant sediment types in South Carolina. The teacher will ask the students to predict the porosity and permeability differences between a predominately sandy area such as the Sandhills and the predominantly clay area such as the Piedmont. They will also predict the differences between groundwater and runoff amounts in these areas. They will write their predictions, either in their journals or on a separate piece of paper, and draw diagrams showing what they think will happen in each of these regions.

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Follow-up questions

• When the water table was at the surface of the marbles, what would happen to the water if the students kept pouring? How does this correlate with what happens in nature?
  
• Leave the permeability part of this activity set up for one day and then have students measure how much water flowed through to the beaker below, how much water was retained in the sediment, and how much water (if any) remained on top of the sediment. Does all 200ml of water ever flow through for any of the sediment types? Does the water ever completely seep through the clay? How much water is retained in the different sediments? Have students research how sediment can hold on to water.
  
• How would roads and buildings affect the porosity and permeability of the area they are on?
  
• When water soaks into sand, would some of the water molecules enter the spaces between the atoms in the sand grain? Can water “dissolve” in sand the way salt dissolves in water?