How to Make a River Model

River models, also called stream tables, are easy to construct and provide an excellent way to demonstrate how moving water changes Earth's surface, an important concept in Earth science. River models can be used to demonstrate erosion and deposition, illustrate how the slope and speed of water flow affect erosion, and show how meanders, lakes and deltas are formed. Ideally, there should be one river model for each group of 4-5 students so they can carry out their own experiments, but if resources are limited, it can be done as a demonstration by the teacher. This is also an easy and fun project to do at home.

Materials needed:

Large, shallow plastic tub (at least 20 inches long and 5 inches deep)

Diatomaceous earth (available at swimming pool supply stores)

Disposable dust mask

Container for water (ideally should have a wide mouth and hold 1-2 liters)

Flexible plastic tubing

Screw clamp or pinch clamp to control the rate of water flow (if clamps are unavailable, a binder clip or paper clip can be substituted)

Precaution: dust from dry diatomaceous earth should not be inhaled, and can irritate the eyes. Remove contact lenses or wear safety goggles, and wear a dust mask when working with dry diatomaceous earth. Take care when mixing it with water, and make sure the diatomaceous earth is wet before the students have access to it. Once it is wet, there is no danger of inhaling the dust.

Place several cups of water in the plastic tub and add diatomaceous earth to the water. Mix with a trowel or large spoon until it is thoroughly wet. Tilt the tub by resting one end on a book or piece of wood to raise it several inches, then lift the lower end of the tub and bang it on the table several times. This causes the diatomaceous earth to form a slope on the bottom of the tub.

You are now ready to create your river model. Place the container of water on a book or block of wood at the uphill end of the tub. Fill an approximately 1 foot length of plastic tubing with water and remove all air bubbles. Insert one end of the tubing into the container to the bottom and clamp the other end so the water cannot escape. The clamped end must be below the level of the surface of the water to create a siphon.

Hang the clamped end of the tubing over the uphill end of the tub. Open the clamp so that the water drips out onto the surface of the diatomaceous earth. As the water drips, a river will be cut into the earth. The water can be colored with blue food coloring if desired, but the rivers are easily visible even without the coloring.

Students can carry out experiments to observe how the depth and shape of the river are affected by the speed of flow, the slope of the tub, and the length of time the water is allowed to flow. The speed can be adjusted by how tightly the tube is clamped. A flow rate of two drops per second is a good average, and it can be increased or decreased to observe the effect of flow rate on erosion. The slope can be adjusted with books or blocks of wood under the uphill end of the tub.

As the water flows into the river, it will accumulate into an "ocean" at the downhill side of the tub and will need to be removed periodically by scooping it out with a plastic cup. Pour the water into another container and allow any diatomaceous earth to settle before discarding the water, so that it doesn't get poured down the drain.

Keep the water in the container replenished so that the level does not fall below the end of the tubing, or the siphon will not work.

The river models can be stored and reused indefinitely. If the tubs don't have lids, place large plastic garbage bags on top of the diatomaceous earth and then stack the tubs on top of one another.

References:

River Cutters, Great Explorations in Math and Science (GEMS) Teacher's Guide, Lawrence Hall of Science, UC Berkeley, California, 2003. ISBN 0-924886-32-3

Personal experience