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Rivers and Streams

Rivers convey the excess waters of the land areas that they drain to larger bodies of water or directly to the oceans. Collectively, they represent the world's WATER RESOURCES, as they carry virtually all the water that is available for human management and use.
The four great civilizations of early human history developed in close dependence on rivers and the fertile, easily worked soils of their floodplains: the Sumerians on the TIGRIS and EUPHRATES rivers in Iraq, the Harrapans on the INDUS in Pakistan, the Chinese on the HWANG HO ("Yellow River") and the YANGTZE RIVER in central China, and the Egyptians on the NILE RIVER in Egypt. Rivers and their valleys have continued to play important roles in the course of history; the exploration of much of North America was via river routes, and most of its major settlements are adjacent to rivers.
In addition to providing direct sources of water for domestic, agricultural, and industrial uses, rivers produce energy directly through hydropower generation they also provide the cooling water for many fossil and nuclear-fueled power plants. They serve as transportation routes, as carriers and natural "treatment plants" for human wastes, and as the habitats of ecologically, economically, and recreationally valuable fish and wildlife. The continually changing nature of rivers and their often spectacular scenic features make them a source of inspiration for many writers and artists, as well as for more casual observers.
On a global basis, the significance of rivers as a water resource lies not in the amount of water they contain at a given time (only about 0.14% of the Earth's liquid freshwater and about 0.01% of all water), but in their average discharge, which is the total volume carried in a given time period. Worldwide, this amounts to about 39,000 cu km per year, or, expressed differently, 28 trillion gallons per day. The flow of the Amazon is about five times greater t...

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