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Before class, I prepare several "Darcy columns". These are plastic water bottles with a hole in the bottom that is covered with mesh and a rubber stopper. The bottles are filled with soil and water and are capped. One bottle is the reference bottle, with sand of height hs, and water of height hw, and a standard bottle diameter. Each of the remaining bottles are filled with one of the parameters varied: e.g., gravel instead of sand, silt instead of sand, sand of height 2hs instead of hs, water of height 2hw instead of hw, larger diameter bottle, etc. In class, student split into groups and each group is given a bottle, flexible ruler, funnel, graduated cylinder, and a large cup of water. As a group, they note the material type, measure the flow area, measure the height of porous material, and measure the difference in head across the porous material. Then they measure the flow rate, while maintaining a constant head. They repeat the flow measurement for their column, and then they repeat the process with one or more other columns, depending on the time available. Each group records their results on a table, and the class results are tabulated on the board. As a class, we discuss the whether or not their results follow Darcy's law. We also discuss the measurement errors, repeatability of the results, and the differences in flow rate for sand, gravel, and silt.
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