Page 262 - Encyclopedia Of World History Vol V

water management 2039

tile pipes.The pipes, with holes in them, are installed in of the low land behind the dikes. They ganged together
ditches in the fields and then covered up.The lower end large windmills to lift the water out of the low land and
of the pipes must drain into something, usually a river dump it into the sea or a river outside the dikes. However,
bed. Tile pipes are effective and virtually invisible to all the height to which water could be raised was limited,
but the most discerning eye. and the windmills could operate only when the wind was
Another way to drain water is to dig dirt out of a the right speed.
swamp and pile it up so that the top is above the water With the advent of the heat engine during the Indus-
level, producing what are often called “raised fields.” trial Revolution the limits on lifting water were elimi-
These fields can vary in size from a few square meters at nated. One of the first tasks that people gave to steam
the edge of a swamp to thousands of hectares. Among engines was to drive pumps that drained water from
the earliest water management systems using raised fields flooded coal mines. Later uses included pumping
were in highland New Guinea, dated to about 5000 BCE. drainage water out of a basin and lifting water for irri-
gation. People could lift water from a surface source (such
Lifting Water as a river or lake) or from a deep well. Today people
Because of water’s weight and liquid nature, people had acquire a great deal of irrigation water from deep under-
difficulty lifting water for many millennia. People used ground, and they could not do this without the heat
human muscle to lift small amounts of water in pots to engine to drive a pump.
water individual plants in the Valley of Oaxaca, Mexico, With the introduction of the internal combustion
about 2000 BCE. People in Egypt could lift larger engine, small pump and driver (an engine that powers the
amounts with the shadoof (a beam on top of a pole, with pump) sets became feasible, even to the point that farm-
a counterweight at one end and a container for the ers could own such sets and move them around the farm
water on the other end). Human muscle powered the to where they were needed. However, although such sets
shadoof. People have dug wells (vertical shafts from the save labor, they are expensive in terms of energy.
surface down to the water table) for a long time, but A modern innovation in irrigation technology is the
extracting large amounts of water has been difficult. Peo- pressurized system. Two major forms are used: sprinkler
ple have used large domesticated animals to power the systems and drip systems. In sprinkler systems a pump
raising of larger amounts of water, but the output has not and driver pressurize water, which is then moved through
been substantial. a series of pipes that is above the level of the plants that are
In the dry mountain belt from Turkey to western to be irrigated.These pipes have multiple nozzles, and the
China, horizontal wells (called “qanats” or “foggara”) water distribution mimics a light rain.Two major advan-
were widespread. People dug a shaft from the point of tages of this system are: (1) Water use is much more effi-
use (often an oasis) into a mountain, gently sloping cient (more than 90 percent of the water reaches the crop
upward, until the shaft met with water-bearing earth. Peo- root zone; by contrast,ditches have efficiency as low as 50
ple dug vertical shafts down to the horizontal shaft to percent), and (2) no need exists to sculpt the surface of the
remove dirt and to gain access for repairs. Horizontal soil, thus saving labor and energy. A small computer can
wells could exceed 60 kilometers in length. They could operate a number of these sprinkler systems, saving even
provide water for centuries if properly maintained. more labor.These systems also can deliver chemicals (fer-
The first major innovation that increased people’s tilizers, pesticides) in the water.The major disadvantage is
ability to lift water was the windmill, which became that the technology is energy intensive. However, people
prominent in northwestern Europe during the thirteenth use sprinkler systems throughout much of the world;
century. The Dutch reclaimed low land from the sea by people flying in an airplane at 10,000 meters can see the
building protective dikes and then draining the water out green circles made by a rotary sprinkler system.