The difference between the two types of canal is this: A sea-level
canal contemplated an excavation from shore to shore at the level of
the sea; a lock canal contemplated the construction of a great dam
across the valley of the Chagres and the course of the Chagres river,
which dam would have the effect of holding the waters of the Chagres
river. The accumulation of those waters in time would form a lake,
the surface of which lake, of course, would be considerably above the
level of the sea on either side. The dam would necessarily have to be
surmounted through the agency of locks.
After much controversy and bickering, and a great deal of muck-raking
by the newspapers and magazines of the United States and Europe, the
plan of a lock canal was finally adopted. This plan contemplated the
impoundment of the waters of the Chagres river by a dam constructed
at Gatun, a little village about three and one-half miles inland
from the shore of Limon bay. This dam when finished would be 7700 feet
in length, half a mile in width at the base, and 135 feet in height.
It was designed that this dam should hold the waters of the lake at
a height of 85 feet above sea-level, but it was constructed 50 feet
higher so that all danger might be obviated in case of excessive floods.
[Illustrations: AT WORK IN THE CULEBRA CUT.]
The plan of the canal contemplated that this dam should be surmounted
by three locks constructed in pairs, so that in case one series of
locks became impaired the other could be used, or ships might pass up
one side and down the other at the same time. Each of the locks was to
be 1000 feet long, 110 feet wide, and have a lifting capacity of 28½
feet. Therefore, when completed, this series of locks constructed of
concrete would be more than 3000 feet in length and about 250 feet in
width, without doubt the largest concrete formation ever constructed.
The engineers of the Panama Commission give four reasons for the
adoption of the lock system instead of the sea-level type. In the first
place, it would take twice as long to construct a sea-level canal as
it would a lock canal. Secondly, it would cost twice as much money,
and as the lock canal system is costing nearly four hundred millions
of dollars, the difference in cost would be a great obstacle to the
construction to the other type of canal. The third reason was that in
case a sea-level canal was constructed it would be necessary to place
locks somewhere along its course because of the fact of the variation
of tides between the Atlantic and the Pacific Oceans.
The tide rises and falls at Colon, on the Atlantic side, about 3½ feet,
at the time of extreme high tide; while on the Pacific side the tides
rise and fall 27½ feet, and this great variation would cause a current
to rush through the course of the canal so great that locks would be
required for its control.
But the fourth was the most potent reason of all why the lock system
was adopted. On the Isthmus of Panama the rainfall amounts to 130 to
150 inches annually. Sometimes the precipitation will amount to 10 or
12 inches in twenty-four hours. The Chagres river is the only agency
for the drainage of a vast area of water-shed in the Caribbean sea.
Therefore, at times the Chagres river might be a small, inconsequential
stream that a boy could wade across, and yet before twenty-four hours
had elapsed, because of a heavy rainfall, it might have swelled into
a raging torrent that would wreck the strongest battleship of the
American navy. The large volume of water discharged by the Chagres
river could not be turned into the canal proper, as the currents and
the rush of flood waters would soon impair the banks of the canal.