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# Soil Permeability

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• What particles make up soils?
• What are the physical characteristics of soils?
• How can soil type affect surface water runoff?
• How can soil type affect erosion?
• How can soil drainage affect surface water runoff?
• How can soil drainage affect erosion?
• What is a percolation (perc) test?
• What does a perc test tell us?

Soils are composed of three types of particles: sand, silt, and clay.The size of the particles varies, with clay having the smallest size and sand the largest.Smaller sized particles pack more closely together and slow the flow of water through the soil.The composition of a soil can affect the permeability of water to flow through the soil.In this experiment, the student will test the permeability of soils to water.This information can be useful in determining how the soils can affect surface water runoff and erosion.

• 1 large coffee can
• Can opener
• 9 1L bottles
• Metric ruler
• Permanent marker
• Stopwatch/timer
1. Remove the top and bottom of the coffee can to create an open metal cylinder.On the inside of the coffee can, measure 3 cm up from the bottom and make a mark with your permanent marker.Repeat this several times around the bottom of the can.Connect the marks to create a line around the inside of the coffee can 3 cm from the bottom.Repeat on the outside of the can.
2. Fill your 9 bottles with 1L of water each.Take the can, the water bottles, and a timer with you outside.Choose three locations to perform your perc test.Make sure that the locations are in very different places with different plant communities and human influences.Write your hypothesis as to which soil will be the most permeable and which will be the least and why.
3. At each location, you will perform the perc test three times.You will average the results to get your drainage time for each soil.At the first location, press the coffee can into the ground to the 3 cm mark.Have the timer ready to start as soon as the water touches the ground.Slowly pour a bottle of water (1L) onto the soil.Stop timing when all the water has drained into the soil.Record the time.Repeat two more times in two different spots at the first location.
4. Repeat the entire procedure for the second and third locations.Average your times at each location to come up with your average drainage time.Create a bar graph to show your results.Compare the results to your hypothesis.Draw conclusions about the permeability of each soil and how that might affect surface water runoff and erosion at that location.

Terms/Concepts: Soil texture; Soil composition; Soil permeability; Percolation (perc) test; Soil porosity;Clay; Silt; Sand; Loam; Surface water runoff; Erosion

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