Rivers and Waterways

Introduction

A river is a natural, flowing stream of water that provides an avenue for drainage of water from higher elevations to a standing body of water at lower elevations, which is typically a lake or ocean. Some rivers, however, provide avenues for drainage directly into the groundwater table (for example, a river draining into a sinkhole or a river draining into porous materials lying above the groundwater table). In a river, the flow of water is generally confined to a channel or a network of interconnected channels except when the discharge of water exceeds the river’s channel capacity. In that instance, the river temporarily spreads out beyond its channel to a surrounding floodplain until the flood subsides.

A waterway, by contrast, is defined as a body of water that is navigable by boat. This is usually taken to mean a commercial vessel or boat, but a broader definition is any type of boat or floating means of conveyance. A waterway can be a natural feature, a human-made feature, or a natural feature modified by humans. A water-way can be a river, but this concept also includes lakes, oceans, and human-made canals. For a waterway to be navigable, it must be deep enough to accommodate the type of boat at issue (waterway draft), it must be wide enough to accommodate the boat (waterway beam width), it must be free of rapids or waterfalls (or have a way around such features, for example, locks and dams), and it must have a water current velocity that allows boats to move easily against the current. In addition to the world’s oceans and large lakes such as the North American Great Lakes, other well-known waterways are the Erie Canal (United States); the Intracoastal Waterway (United States); the Panama Canal (Panama); the St. Lawrence Seaway (Canada); the Suez Canal (Egypt); and the Tennessee-Tombigbee Waterway (United States).

Historical Background and Scientific Foundations

Water flows across the surface of Earth in response to the force of gravity. Thus, surface water always flows naturally in a downhill direction. The slope or gradient of Earth’s surface can be very steep in mountainous terrains and very low in plains areas or low-lying coastal areas. However, even a very slight gradient, or slope, will cause water flow. Ever since Earth first had a solid, rocky crust, meteoric water (water than falls as rain) has flowed over the surface. We know this because the oldest rocks on Earth are thermally altered sediments once deposited in river channels and on shorelines.

Rivers have had a profound effect upon the landscapes that we see on Earth’s surface. From space, we can see that almost all the land surface has been eroded to one degree or another by the action of running water in streams and rivers. Areas with high rainfall, or that had high rainfall in the past, are the most profoundly affected by the action of running water. Nearly all Earth’s surface that is not covered by water or ice is divided into drainage basins. A drainage basin is the area drained by a river system. All rainfall within a drainage basin flows out of that basin through a series of interconnected streams and rivers. Smaller streams and rivers feed into progressively larger rivers, which are referred to as higher order rivers. With higher order rivers, the size of the river and amount of water in the river increase downstream, and the gradient of the river decreases as well.

Impacts and Issues

Humans have used rivers as waterways since the time of nomadic tribes and hunter-gatherer groups. Initially, humans used rivers as resource areas for water and food, but rivers also provided means for transportation. With the advent of civilizations, humans commenced making modifications on rivers, including damming and altering the channels of rivers to accommodate various means of water transportation. As land transportation developed, rivers and waterways were spanned by bridges and bypassed by tunnels. In the past, it was common for rivers to be partially blocked by huge masses of downed trees floating in the river, called log jams. Log jams are rare today and, in fact, most rivers that we see today are managed and controlled by dams or other artificial means.

It is unusual to see a completely natural or uncontrolled river, even in remote areas. In many areas, dams on rivers are used to generate power (called hydroelectricity). In hydroelectric power generation, the flow of water is used to turn turbines, which in turn generate electrical power. Rivers have also become waste disposal avenues with the advent of manufacturing processes that generate liquid wastes. For this reason, may rivers in manufacturing areas are highly polluted or have been polluted in the recent past.

See Also Floods; Surface Water

BIBLIOGRAPHY

Books

Barry, John M. Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America. New York, Simon and Schuster, 1998.

Web Sites

Mississippi Development Authority. “The Tennessee-Tombigbee Waterway.” 2007. (accessed April 16, 2008).

U.S. Environmental Protection Agency (EPA). “The Great Lakes.” March 4, 2008. (accessed April 16, 2008).

David T. King Jr.

WORDS TO KNOW

EROSION: The wearing away of the soil or rock over time.

HYDROELECTRICITY: Electricity generated by causing water to flow downhill through turbines, which are fan-like devices that turn when fluid flows through them. The rotary mechanical motion of each turbine is used to turn an electrical generator.

SEDIMENT: Solid unconsolidated rock and mineral fragments that come from the weathering of rocks and are transported by water, air, or ice and form layers on Earth’s surface. Sediments can also result from chemical precipitation or secretion by organisms.