From outer space, the earth looks like it is covered with veins and arteries, similar to our bodies.
The earth's arteries, however, are really a vast web of rivers and streams that channel water across the planet, from mountains to oceans. Although there are many rivers and streams, these sources of running water account for a very small portion of the earth's total surface, just .3%.
A tributary is a river that feeds into another river, rather than ending in a lake, pond, or ocean. If a river is large, there’s a good chance that much of its water comes from tributaries. How do geographers decide which river is the “main” river and which is the “tributary” when they’re naming rivers? Usually the bigger river gets to be the “main” river, but sometimes history or other factors come into play.
Up And Down, Right And Left
"Downstream" always points to the end of a river, or its “mouth.” “Upstream” always points to the river’s source, or “headwaters.” As you look downstream, your right hand corresponds to “River Right.” Your left hand corresponds to “River Left.” As in, “Hey, river cleanup volunteers - here’s a nasty tire downstream on River Left! Let’s go get it!”
Source / Headwaters
The beginning of a river is called its source or headwaters. Even if a river becomes big and powerful, its headwaters often don’t start out that way. Some headwaters are springs that come from under the ground. Others are marshy areas fed by mountain snow. A river’s headwaters can be huge, with thousands of small streams that flow together, or just a trickle from a lake or pond.
What happens in the headwaters is very important to the health of the whole river, because anything that happens upstream affects everything downstream.
The shape of a river channel depends on how much water has been flowing in it for how long, over what kinds of soil or rock, and through what vegetation. There are many different kinds of river channels – some are wide and constantly changing, some crisscross like a braid, and others stay in one main channel between steep banks. The bends in a river called meanders are caused by the water taking away soil on the outside of a river bend and laying it down the inside of a river bend over time. Each kind of river channel has unique benefits to the environment.
The land next to the river is called the riverbank. This is an important, nutrient-rich area for wildlife, replenished by the river when it floods. In the West, these riverside areas provide habitat for more bird species than all other vegetation combined. These areas also provide valuable services like protection from erosion during floods, and filtering polluted run-off from cities and farms.
Floodplains are low, flat areas next to rivers, lakes and coastal waters that periodically flood when the water is high. The animals and plants that live in a floodplain often need floods to survive and reproduce. Healthy floodplains benefit communities by absorbing floodwaters that would otherwise rush downstream, threatening people and property.
The end of a river is its mouth, or delta. At a river’s delta, the land flattens out and the water loses speed, spreading into a fan shape. Usually this happens when the river meets an ocean, lake, or wetland. As the river slows and spreads out, it can no longer transport all of the sand and sediment it has picked up along its journey from the headwaters. Because these materials and nutrients help build fertile farmland, deltas have been called “cradles” of human civilization. Deltas are “cradles” for other animals as well, providing breeding and nesting grounds for hundreds of species of fish and birds.
Wetlands are lands that are soaked with water from nearby lakes, rivers, oceans, or underground springs. Some wetlands stay soggy all year, while others dry out. Although wetlands are best known for providing habitat to a wide variety of plants and animals, they also help protect our communities by acting as natural sponges, storing and slowly releasing floodwaters. A single acre of wetland, saturated to a depth of one foot, will retain 330,000 gallons of water – enough to flood thirteen average-sized homes thigh-deep. Wetlands also help provide clean water by naturally filtering out pollution.
Flow refers to the water running in a river or stream. There are two important aspects to a river’s natural flow. First, there is the amount of water that flows in the river. Some rivers get enough water from their headwaters, tributaries, and rain to flow all year round. Others go from cold, raging rivers to small, warm streams as the snowpack runs out, or even stop flowing completely. A river’s natural ups and downs are called “pulses.” Like a human being’s pulse, a river’s natural flow of water is life support for animals, plants, and fish, delivering what they need to survive at the right times. When we divert water away from a river, we change the river’s natural flow.
The second component of natural flow is how water moves through a river’s channel. In a natural, wild river, the water runs freely. But in more developed or degraded rivers, dams and other structures can slow or stop a river’s flow. When a river’s flow is blocked, migratory fish like salmon can suffer, unable to move up or downstream.
River and Stream Links
All Along A River - Find out more about the physical processes of rivers such as erosion, factors that influence velocity and volume, and drainage patterns. This site also includes case studies of the Singapore and Rhine rivers. A great site created by Chinese high school students.
Earth's Water—Rivers and Streams - Site by the USGS discusses rivers and streams including what they are, their sources, and their impact on the landscape.
Rivers and Streams - Site by the EPA covers what is a river or stream and how to keep them healthy.
American Rivers - This site contains information about how rivers are formed, river food webs, and more.
Rivers of Life—River of Resources - River stories, profiles of the world's mightiest rivers, maps, and more.
Streams - This site by the Gulf of Maine Aquarium looks at stream ecology and human impact.
U.S. Environmental Protection Agency - Watersheds - Find out about your local watershed.
Watersheds - Learn about how rivers and streams are formed.
Interactive Games and Activities
Virtual Tour of a Drinking Water Treatment Plant - A flash-based step-by-step how water is treated and delivered to your home or business as water that is safe to drink.
Interactive Word Scramble Game * - A flash animated game that lets you unscramble one word in a sentence and lets you know instantly if you have the right answer.
Splash! An interactive computer game that delivers information on non-point source pollution in a fast-paced and entertaining format. Appealing for audiences of all ages, it teaches fundamental concepts about non-point source pollution prevention measures in a farm, city, and neighborhood setting. Point and click screens that move and have sound help players learn how day-to-day decisions can affect the water quality of lakes and streams
Interactive Fun Facts Matching Game * - A flash animated game that lets you match amounts of water to the correct everyday water usage item and lets you know instantly if you have the right answer.
Interactive Question & Answer Game *- A flash animated game that gives the Answer and you have to choose the correct Question from three possible answers. The game lets you know instantly if you have the right answer.
Interactive Build Your Own Aquifer Instructions* - A step-by-step instruction on how to complete this in class activity complete with narration and visual support. You can jump from section to section and repeat as necessary.
Interactive Water Filtration Instructions* - A step-by-step instruction on how to complete this in class activity complete with narration and visual support. You can jump from section to section and repeat as necessary.
Water Treatment Cycle - An illustration of the water treatment process.
Drinking Water Bloopers - Embarrassing moments in the life of a water drinker.
Water Facts of Life - Amazing facts about water.
Water Trivia Facts - Fun water facts continue - how long can you live without water?
Be Hydro-logical - Find out what you can do.