Managing Semi-Arid Watersheds: Watershed Basics - What is a Watershed?

"Watershed" is a new term to many people. Its definition is almost as simple as the well-known phrase "water runs downhill". The drain board that carries rinse water into your kitchen sink can be compared to a watershed. On the land, water that does not evaporate or soak into the soil usually drains into ditches, streams, marshes, or lakes. The land area from which the water drains to a given point is a watershed.

When you were a small child, you probably had a favorite mud puddle in which you liked to play. The part of the yard from which the water drained into the puddle was its watershed. Possibly a small stream ran by your house. It may have been dry most of the year or it may have flowed continuously. Water from a few acres drained into that little stream. Those few acres were its watershed. This small stream and others like it ran into a larger one. The land areas drained by the small steams made up the watershed of the larger stream into which they flood. Small watersheds make up the larger ones. The Mississippi River, for example, drains a watershed of about 1,243,000 square miles. This large watershed is made up of thousands of smaller ones. So wherever you live you are in a watershed. It can be just your own backyard or the area drained by a small creek or by a large river.

You and the other people who live in the watershed are part of the watershed community. So are the animals, the birds, and the fish. All depend on the watershed, and they, in turn, influence what happens there. What happens in your small watershed also affects the larger watershed downstream.

If water runs off the land too fast, it cuts gullies and carries off topsoil. This soil along with other debris the water carries into streams and lakes may spoil fishing. As soil fills the lakes or reservoirs, the amount of water they can hold is reduced. Therefore the water supply for your town and your home may be reduced. Although erosion is a natural process, accelerated erosion degrades productivity of the land. Such sediment carried downstream by runaway water may greatly increase the cost of filtering the water you get from the faucet. It can interfere with the hydroelectric plant that produces your electricity. This may make your electric bills higher.

If too much water runs away too rapidly, it causes a flood that damages farms, ranches, crops, property, homes, highways, and utilities. It may take lives. Stream channels may be choked with sediment. Then the flood is more serious because the choked-up channels carry less water. However, much of our productive farmland was created by flood waters that deposited soil. This soil was eroded from the uplands of the watershed.

Water can be slowed down and used to advantage when soil and water conservation practices and other flood-prevention measures are put in over all the watershed. Terraces, strip cropping, more grass and legumes in crop rotations, and improved pastures are practices that make more water soak into the soil. Small dams can hold back runoff water that would otherwise cause flood damage. Conservation irrigation systems waste less water and thus leave more for other irrigators to use. Later some water will go into streams, lakes, or underground storage to be used in other ways. It doesn't carry sediment to clog streams and water supplies. Thus, more water is available for the many uses people make of it.

See also: Beaver Creek Watershed Field Day Questions