There are other
places in the world where this may be also done for a great profit. The best that I know of is the Nile
itself. Far enough south it is possible
to divert the surplus waters of the flood season into the Western desert to
drain into the deep basin there that remains cut off from the
Mediterranean. I would also go further
and open a ditch to the Mediterranean as well to actually fill this basin. Thus irrigation from the Niles overflow can
support extensive woodland and agriculture on both sides of this inland sea
while evaporation from the water will also support the hydraulic cycle around
the lake and likely far to the East.
It is also easy
to see the inspiration for the Grand Canal.
They understood possibility.
Diverting water
from Siberia into area of the Aral sea has also been seriously discussed
although that would be more a dam based system.
The legacy of
Dujiangyan: China’s ancient irrigation system
Dujiangyan is the oldest and only surviving non-dam
irrigation system in the world, and a wonder in the development of Chinese
science. Built over 2,200 years ago in what is now Sichuan province in
Southwest China, this incredible feat of engineering is still in use today to
irrigate over 668,700 hectares of farmland, drain floodwater, and provide water
resources for more than 50 cities in the province. Dujiangyan is
now undergoing its largest renovation in over a decade.
More than two millennia ago, the region in which
Dujiangyan now stands was threatened by the frequent floods caused by flooding
of the Minjiang River (a tributary of the Yangtze River ). Li Bing, a local
official of Sichuan Province at that time, together with his son, discovered
that the river was swelled by fast flowing spring melt-water from the local
mountains that burst the banks when it reached the slow moving and heavily
silted stretch below. One solution would have been to build a dam but Li
Bing had also been charged with keeping the waterway open for military vessels
to supply troops on the frontier, so instead he proposed to construct an
artificial levee to redirect a portion of the river's flow and then to cut a
channel through Mount Yulei to discharge the excess water upon the dry Chengdu
Plain beyond.
Li Bing received funding for the project from King
Zhao of Qin and set to work with a team said to number tens of thousands. The
levee was constructed from long sausage-shaped baskets of woven bamboo filled
with stones known as Zhulong and held in place by wooden tripods known as
Macha. The system uses natural topographic and hydrological features to solve
problems of diverting water for irrigation, draining sediment, flood control,
and flow control without the use of dams.
Cutting the channel through Mount Yulei was a
remarkable accomplishment considering that this project was undertaken long
before the invention of gunpowder and explosives, which would have enabled the
builders to penetrate the hard rock of the mountain. But Li Bing found another
solution. He used a combination of fire and water to heat and cool the
rocks until they cracked and could be removed. After eight years of
work a 20 metre wide channel had been gouged through the mountain.
After the system was finished, no more floods
occurred. The irrigation made Sichuan the most productive agricultural place in China and the people have been living peacefully
and affluently ever since. Now, the project is honoured as the 'Treasure of
Sichuan'.
Dujiangyan, now a UNESCO World Heritage Site, is
admired by scientists from around the world, because of one feature. Unlike
contemporary dams where the water is blocked with a huge wall, Dujiangyan still
lets water go through naturally, enabling ecosystems and fish populations to
exist in harmony.
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