42
DOCK ENGINEERING.
range between low water of spring tides in the dry season, and the average
higli water in the rainy season is about 18 feet, but during heavy floods has
been as much as 22J feet.”*
Eig. 11. —KidderpurODocks, Calcutta.
Such conflicting conditions
call for a special arrangement
of dock entrances to permit of
vessels entering or leaving on
the flood tide, or when the
current in the river is continu-
ously down stream, and the
arrangement adopted is shown
in fig. 11. It consists of a lock,.
400 feet long by 60 feet wide,
and a single entrance, 80 feet
wide, pointing in opposite direc-
tions, the reasons for and ad-
vantages of which are fully
discussed in Chapter vi.
The half-tide basin is 600
feet by 680 feet, and No. 1 dock
is 2,600 feet long by 600 feet
wide, with a water area of 34^
acres.
The Alexandra Dock, Hull.
This dock is selected as an
example of the machicolated
system. It is situated near the
mouth of the River Humber,
has a water area of 46^ acres, a
quayage of 2 miles, covering
160 acres ; and is provided with
a lock, 550 feet long by 85 feet
wide, and two graving docks.
The entrance to the lock is
splayed.
“The navigable channel of
the Humber approaches close to
the northern shore in front of
Hull; but at the Alexandra
Dock the northern edge of the
deep channel was 960 feet from
the outer look sili. The channel
* Bruce on “ The Kidderpur Docks, Calcutta,” Min. Proc. Pist., C.E., vol. cxxi.