Rivers? Streams? Creeks? They are all names for water flowing on the Earth's surface. As far as the Water Science site is concerned, they are pretty much interchangeable. I tend to think of creeks as the smallest of the three, with streams being in the middle, and rivers being the largest.
Most of the water you see flowing in rivers comes from precipitation runoff from the land surface alongside the river. Of course, not all runoff ends up in rivers. Some of it evaporates on the journey downslope, can be diverted and used by people for their uses, and can even be lapped up by thirsty animals. Rivers flow through valleys in the landscape with ridges of higher land separating the valleys. The area of land between ridges that collects precipitation is a watershed or drainage basin. Most, but not all, preciptation that falls in a watershed runs off directly into rivers - part of it soaks into the ground to rechage ground-water aquifers, some of which can then seep back into riverbeds.
A river is nothing more than surface water finding its way over land from a higher altitude to a lower altitude, all due to gravity. When rain falls on the land, it either seeps into the ground or becomes runoff, which flows downhill into rivers and lakes, on its journey towards the seas. In most landscapes the land is not perfectly flat -- it slopes downhill in some direction. Flowing water finds its way downhill initially as small creeks. As small creeks flow downhill they merge to form larger streams and rivers. Rivers eventually end up flowing into the oceans. If water flows to a place that is surrounded by higher land on all sides, a lake will form. If people have built a dam to hinder a river's flow, the lake that forms is a reservoir.
Major rivers of the world.
The water in a river doesn't all come from surface runoff. Rain falling on the land also seeps into the Earth to form ground water. At a certain depth below the land surface, called the water table
, the ground becomes saturated with water. If a river bank happens to cut into this saturated layer, as most rivers do, then water will seep out of the ground into the river. Ground-water seepage can sometimes be seen when a road is built through water-bearing layers, and even on a driveway!
Look at the diagram below. The Earthbelow the water table, the aquifer (the purple area), is saturated, whereas the Earthabove (the pink area) is not. The top layer (unsaturated soil/rock material) is usually wet, but not totally saturated. Saturated, water-bearing materials often exist in horizontal layers beneath the land surface. Since rivers, in time, may cut vertically into the ground as they flow (as the river cuts into the purple section in the diagram), the water-bearing layers of rock can become exposed on the river banks. Thus, some of the water in rivers is attributed to flow coming out of the banks. This is why even during droughts there is usually some water in streams.
The phrase "river of life" is not just a random set of words. Rivers have been essential not only to humans, but to all life on earth, ever since life began. Plants and animals grow and congregate around rivers simply becuase water is so essential to all life. It might seem that rivers happen to run through many cities in the world, but it is not that the rivers go through the city, rather, the city was built and grew up around the river. For humans, rivers are diverted for flood control, irrigation, power generation, municipal uses, and even waste disposal. And, if you ask any of these people recreating on the Chattahoochee River in Atlanta, Georgia what the best use of a river is, they might just say "to have fun."
Sources and more information
USGS real-time river stage/streamflow - National Water Information System
USGS flood information
Largest Rivers in the United States: USGS Open-File Report 87-242
River Science along the Lewis and Clark Trail
National Water-Quality Assessment (NAWQA) Program, assessing water quality in the largest river basins in the United States
Investigate the Water Cycle: Streamflow (in many languages!)
U.S. Department of the Interior | U.S. Geological Survey
URL: http://ga.water.usgs.gov/edu/earthrivers.html
Page Contact Information: Howard Perlman
Page Last Modified: Friday, 12-Jun-2009 08:25:25 EDT
