The spring
being satisfactory, the work proceeds with vigour. We will accept the
first well as forty feet in depth; if the surface of the earth were an
exact level, the next well would be an equal depth; but as the water
retains its natural level, the vertical measurement of each shaft will
depend upon the formation of the upper ground. The object of the
well-sinker is to create a chain of wells united by a subterranean
tunnel, in order to multiply the power of a unit and to obtain the
entire supply of water; he therefore sinks perhaps ten or twenty wells
to the same level, and he cuts a narrow tunnel from one to the other,
thus connecting his shafts at the water-line, so as to form a canal or
aqueduct. Precisely as the mole upheaves at certain intervals the earth
that it has scraped from its gallery, the well-sinker clears his tunnel
by sending up the contents through the vertical shafts fifteen yards
apart, around the mouth of which a funnel-shaped mound is formed by the
debris.
These preliminary walls being completed and the water-volume tested, the
neighbourhood is examined with the hope of discovering other springs
that may upon the same principle be conducted towards the main line of
the proposed aqueduct. It is not uncommon to find several chains of
wells converging from different localities to the desired water-head,
and as these are at higher levels, a considerable hydraulic power is
obtained, sufficient in many instances not only to fill the tunnels, but
to force the water to a greater elevation if required.
Pages:
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73