Instructions for Darcy Tube construction:
Ingredients:
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1 PVC tube, 2-3 foot length, 1.5 or 2” diameter
1 PVC elbow (90°)
1 PVC reducing couple (to serve as funnel at top end of tube)
Small piece of wire or nylon screen, or cheesecloth for bottom end of tube
Duct tape
Well sorted sand or gravel
Graduated cylinder, large measuring cup, or bucket marked with volume to catch water.
Stopwatch
Ruler or yardstick
Pitcher for pouring water in to upstream end.
Instructions (see next page for diagram):
1. Assemble PVC with elbow and reducing couple at top. This will be the “upstream end” of the
tube.
2. Tape the screen or cheesecloth to the other end of the tube. This will be the “downstream end”;
the purpose of the screen is to allow water to percolate through the tube but prevent the sand
or gravel from falling out.
3. Fill the tube with the sand or gravel.
4. For the experiment, the tube will need to be held at a particular slope, using ring clamps or
other supports as desired. After having students measure all relevant aspects of the system
(elevation of each end, length of tube, diameter).
5. Water should be poured in to the upstream end, and water level maintained at a selected level
(i.e. the edge of the reducer, or other visible marker in the reducer/funnel).
6. Once the tube is saturated and water is flowing out steadily, start the measurement with
stopwatch. The best approach is usually to define a pre-set volume, and measure the time
required for that target volume to flow through the tube.
7. Experiment should be conducted at multiple slopes by adjusting the supports for the tube, in
order to investigate the relationship between hydraulic gradient and flow rate.