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Information on Rivers
• Dams (see above) or weirs may be built to control the flow, store water, or extract

energy.
• Levees may be built to prevent river water from flowing on floodplains or floodways.
• Canals connect rivers to one another for water transfer or navigation.
• River courses may be modified to improve navigation, or straightened to increase the
flow rate.

River management is an ongoing activity as rivers tend to 'undo' the modifications made by

man. Dredged channels silt up, sluice mechanisms deteriorate with age, levees and dams may
suffer seepage or catastrophic failure. The benefits sought through managing rivers may
often be offset by the social and economic costs of mitigating the effects of such

management. As an example, in many parts of the developed world, rivers have been
confined within channels to free up flat flood-plain land for development. Subsequent
extreme flood events can inundate such development at very high financial costs and often
with loss of life.

The world's ten longest rivers

Because rivers are approximately fractal in nature it is difficult to measure the length of a

river. The more precise the measurement, the longer the river will seem. Also, it is difficult
to determine where a river begins or ends, as very often, upstream rivers are formed by
seasonal streams, swamps, or changing lakes. These are average measurements.

1. Amazon (6,780 km)

2. Nile (6,690 km)
[8]
3. Jefferson-Missouri-Mississippi (6,270 km)
[9]
4. Yangtze (Chang Jiang) (6,245 km)
5. Yenisey-Angara (5,550 km)
6. Huang He (Yellow) (5,464 km)

7. Ob-Irtysh (5,410 km)
8. Amur (4,410 km)
9. Congo (4,380 km)
10. Lena (4,260 km)

(God's Amazing Landscapes) 18