watersheds.org the world in your watershed search
homewhat's newabout ussite mapcontact us

Earth Hydrology Stream Table

A Stream Table Makes a Miniature Stream

A stream table shows, in miniature, how streams flow through
a watershed and how they behave when the water levels change.

Bob Schulz, shown here in the red shirt, is the Ozark Coordinator of the Missouri Stream Team program. He brought a stream table to West Plains for Earth Day, 2001.
The stream table slopes from one end to the other, like the land a stream flows through. To create a miniature stream, water flows in at the higher end and drains out the lower. In this picture the drain is at the bottom.
A pump circulates the water at about 360 gallons per hour. The flow can be increased or decreased to show how runoff changes with more or less rain. With the stream table, Bob can create low water, high water, or even flood conditions.
Bob starts the demonstration by outlining a stream channel. Streams always want to flow in S-shaped paths, or meanders.
Here, Bob has started the water flowing. The material that the water flows through is specially made to behave the way a stream bank might. It is made of recycled plastic, and has grains of three sizes. They act like fine silt, sand and rock might in a full-size stream.
Here you can see grains of plastic moving downstream (red arrow) along the outside of the S-curve.
Water flows faster around the outside of a curve, and the faster the water goes, the more force it has. More force means that it can lift and carry material from the outside of a curve. But because it moves slower along the inside bank, it drops the material it has been carrying. This is why erosion can occur on the outside of stream banks and why gravel bars build up on inside banks.
Here's a picture taken from the inside of an actual S-curve on Bryant Creek. Here we see how the current has been cutting away at the bank on the outside of the curve, while gravel is building up on the inside bank. The water is 4 or 5 feet deep next to the outside bank. It is just a few inches deep on the near side by the gravel. The faster moving water has cut a deeper channel on the outside curve.
Here Bob has put "trees" into the bank along with some rocks to show how trees can keep the bank from eroding.
Look at the deep place by the rock where the water is flowing in. By holding the bank on the outside of the S-curve in place, the rock has forced the faster water there to go deep instead of wide. The change has caused the water to carve out a deep hole.
Trees do the same thing. Where you can hold the bank in place, you make good fishing holes. How? Besides making deeper holes, the shade the trees make also keeps the water cooler. Cool water holds more oxygen and makes better fish habitat. Keeping trees along the bank means keeping more bass, bluegill and other fish in the stream for fishing!
Here you see "trees" have maintained the banks. Where there are no trees, you can see how the water has kept eating away the outside bank.
On the left (green arrow), the stream below the trees has cut through its bank and is forming a new channel.

Notice how a "gravel bar" (red arrow) is forming in the slower-moving water.

As water spreads out, it moves more slowly. It has less force, and drops sediment on the bottom. The stream gets shallower and shallower. The shallower the water, the less friendly the stream becomes for fishing and boating. The loose sediment often covers the food that fish eat and the eggs they lay, so less fish and other animals are able to live there.

Thanks to Bob Shulz and the Missouri Department of Conservation for the source material in this story.