INGENIEUR
Figure 7. Parallel rods to guide the direction of digging of tunnels
Oil Lamp and Shadow
Unlike the two-rod method that requires people
sighting along rods above and below ground, the
oil lamp method simply requires digging a tunnel
in the direction of the shadow cast.
An oil lamp is seated in the middle of a tunnel
several meters back from the digging face, and a
worker turns his back to the oil lamps and face his
shadow. The oil lamps used have a special design
so that they only cast light in one direction.
This method is so effective that two workers
could dig two tunnels according to the direction
of the shadows in front of them until they finally
connected.
Origin of Karez Wells
Chinese historical documents show that the
sinking method of the karez wells inside Xinjiang
including the Western Region was introduced
by the Han people. The majority of the ethnic
minorities of the northwest borderland had not
mastered the sinking technology by that time. It
was Lin Zexu who stood out among all the people
who advocated and promoted the karez wells as
the most powerful and influential voice in modern
times. Ever since then the karez wells have been
part of the irrigation works.
The karez wells in the Turpan area totalled up
to over 100 sets, among which 538 sets are in
Turpan city, 418 sets in Shanshan and 180 sets
in Toksun. The annual runoff volume of these
karez wells amounts to 294,000,000m 3 which
accounts for 30% of the total irrigated areas in
Turpan area.
However, some Western documents mentioned
that the Turpan karez systems are like the qanats
that were used in Persia and the Middle East. It is
not known who originally created this technology.
Some documents mentioned that qanats started
to be used in Central Asia in about 800 BC.
Modern Technology and the Karez
System
With advances in irrigation technology, deep wells
have been drilled to pump groundwater to meet
growing demands for household and agricultural
use as well as the development of oil fields in the
Turpan area. As a result, the groundwater level
in a shallow aquifer, from where a karez system
draws its water, continues to decline. According to
Guan, et al, groundwater has declined 25m over
10 years in some areas of the Turpan Basin. As a
result, many karezes lost their source water and
went dry.
78 VOL 81 JANUARY-MARCH 2020