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Potable water treatment
Potable water treatment

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2.8 Surface run-off

In some inland drainage areas, all water is removed by evaporation and infiltration. However, precipitation not penetrating the land surface usually runs off the surface along defined channels which have been produced by geological processes, previous storms, or possibly by people. This accelerates the process. Its eventual destination is the ocean, except, of course, where it runs to inland seas such as the Dead Sea. It is in the runoff phase of the cycle that physical intervention by humans has been greatest. People have (Figure 4):

  • harnessed the potential energy of rivers to provide power;

  • curbed erosion in order to protect dwellings and avoid the loss of fertile soil;

  • impounded water for supply schemes;

  • diverted flow for the irrigation of crops and to facilitate navigation; and

  • drained land to improve its agricultural value.

Figure 4
Figure 4 Water in our lives: (a) Itaipu Dam in Brazil
Figure 4
Figure 4 Water in our lives: (b) irrigation channels