sometimes used to raise the bucket, especially in
the case of a deep excavation. The silt sediments
are usually piled around the mouth of the shaft to
prevent floodwater intrusion. In most cases, tree
branches, crop straws, etc. are used to cover the
mouth of the shaft to prevent sandstorm intrusion
and icing.
Open channels and collection ponds
The outlet of a tunnel is also called the dragon
mouth and connects to an open channel to
transfer the groundwater to nearby farmlands or in
a residential area. The locals even put their beds
above or near the ground canals, so they will get a
cool environment for sleeping.
Small collection ponds are often constructed
at the end of the open channels to store water.
There are usually many trees growing around the
small reservoir and people can take water from it.
The system helped to make the Turpan area
an oasis on the Silk Road route. It also helped to
make Turpan an important fruit and vegetable
growing area in China. It is said that in 1949,
about 600 karezes were in use and they supplied
most of the water used for irrigation.
Figure 5: A section of tunnel with blue lights
shining on flowing water
Primitive Instruments used for the
construction of tunnels
Sighting along the parallel rods
Two straight rods are tied together with two ropes
of the same length, so that one rod hangs parallel
to and below the other rod.
One rod is sighted along above the tunnel to
set the correct direction and slope, and the other
rod under the ground would replicate the angle
and could be sighted along for the direction of the
tunnel.
By levelling above ground and multiplying the
inclination by the distance between wells they
calculated what the depth of the next well should
be. Then, by sighting along the two rods above
ground, they make sure the rods are aligned
identically.
Then the worker can dig the tunnel according
to the direction the underground stick is pointing
in. The stick method allows for underground
tunnels to be dug successfully between two
vertical wells.
Figure 6: A section of open channel with water
flowing out of tunnels
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