The Panama Canal
Features of Construction
The Isthmus of Panama connects the two continents
through an elbow or segment of an arc running almost east and west. The canal runs
more nearly north and south than east and west, and the Pacific end of it is east of the
Atlantic end. The starting point in Limon Bay lies at latitude 9º 23' north by
longitude 79º 56' north by 79º 32' west.
The distance by air from shore to shore of this narrow part of the Isthmus is about 30
miles. The canal is 43.84 nautical miles in length from deep water to deep water.
It passes through a varied and picturesque country, at places rugged, and where
Gaillard Cut [Culebra Cut] goes through the Continental Divide the lowest point was
formerly some 700 feet above sea level. The route selected has, in general, followed
the valley of the Mindi and Chagres Rivers on the Atlantic slope of the divide, and the
valley of the Rio Grande on the Pacific slope. Sea-level channels were dredged
inward from either end of the canal as far as practicable -- that is, from deep water in
the Pacific northward to Miraflores, and from deep water in the Atlantic southward to
Gatun -- and two artificial lakes were formed by damming the waters of the rivers at
higher levels, one, the Miraflores Lake, extending between Miraflores and Pedro Miguel,
with surface 54 2/3 feet above sea level, and the other, Gatun Lake, extending from Pedro
Miguel to Gatun, with surface 85 feet above sea level. Gaillard Cut, which is
approximately 8 miles long, forms the southern arm of the Gatun Lake. The locks at
Miraflores, Pedro Miguel, and Gatun are used as elevators for raising and lowering vessels
between the levels mentioned.
From the initial station in Limon Bay, on the Atlantic side, the canal runs almost due
south 7 miles in a sea-level section reaching to the valley of the Chagres at Gatun.
Here is the great Gatun Dam, nearly a mile and a half long, closing a gap through
the western end of the Quebrancha Range. The dam is an artificial ridge formed by
pumping an impervious core of dredged clay and sand between parallel ridges of
"toes" of rock and earth. Its construction, across swampy bottoms, was
considered the most difficult feature of the canal. The top was smoothed over with
earth, and the part of the slope on the lake side, lying between levels 10 feet above and
10 feet below the normal water surface, has been riprapped with hard rock to protect
against wave erosion.
As completed, Gatun Dam is about half a mile wide at the base and 100 feet wide at the
top, which is 103.5 feet above sea level. It contains 10,728,965 cubic yards of wet
fill and 12,229,104 cubic yards of dry fill, a total of 22,958,069 cubic yards, which is
more than one-sixth of the total excavation from Gaillard Cut to date.
Near the center of the dam is a concrete spillway, for discharging the surplus waters of
the lake into the lower channel of the Chagres. The discharge channel is 285 feet
wide and 1,200 feet long; and the spillway dam across its upper end is 808 feet long,
being in the form of an arc of a circle. The top of this dam is 69 feet feet above
sea level, and is surmounted by regulating gates 20 feet feet high, the tops of which are
accordingly at elevation 89 feet, or 2 feet above the proposed maximum elevation of the
lake. The 14 regulating gates are installed between vertical concrete piers and are
raised and lowered by means of chains running over sheaves at the top of the piers and
down through the piers to the operating machinery in the body of the dam. The
operating machinery is accessible by means of a tunnel through the center of the spillway
dam, and may be operated by remote control from a switchboard in the hydroelectric
station, which is situated on the east side of the spillway discharge channel. When
all the gates are open the discharge of water is greater than any known rate of run-off
from the Chagres watershed. Dropping down the 60-foot slope of the ogee and striking
against the baffle piers at the bottom, the water makes a turbulent fall which is one of
the most beautiful sights on the Isthmus.
The hydroelectric station uses water from Gatun Lake for driving three turbo-generators of
2,000-kilowatt capacity each, which supply electricity for the operation of the lock and
spillway machinery, the terminal shops and adjacent facilities, and for the lighting of
the locks and the canal villages and fortifications. Transmission over the Zone is
effected through four substations and a connecting high voltage transmission line which
follows the main line of the Panama Railroad.
Gatun Lake, impounded by Gatun Dam, has an area of 164 square miles when its surface is at
the normal elevation of 85 feet above sea level, and is the largest artificially formed
lake in the world. The area of the watershed tributary to the lake is 1,320 square
miles. During the rainy season, from April to the latter part of December, the
run-off from this basin exceeds considerably the consumption of water, and the surplus is
discharged through the spillway of Gatun Dam. Toward the end of rainy season the
surface of the lake is raised to about 87 feet above sea level, in order to afford a
surplus or reserve supply to keep the channel full to operating depth during the dry
season, in part of which the consumption and evaporation are in excess of the supply.
It is calculated that when this level has been attained at the beginning of the dry
season the reserve is sufficient to assure a surface elevation of at least 79 feet at the
end of the dry season in spite of the consumption at the hydroelectric station, and
allowing 41 passages of vessels through the locks each day with the use of the full length
of the chambers, or 58 lockages a day when the shorter sections of the chambers are used
and cross filling employed which would usually be the case. This is a greater number
of lockages than can be made in one day.
The creation of the lake made it possible to have a channel 45 feet deep with its bottom
at 40 feet above sea level. by following the valley of the Chagres as far as Gamboa,
24 miles of channel were thus completed with relatively little excavation. At the
same time the lake, by backing water far up the valleys of the Chagres and its
tributaries, deadens the currents of the rivers before they reach the canal channel and
decreases silting to a minimum.
At Gamboa the Chagres Valley turns sharply to the east and the line of the canal leaves it
for the heavy cut through the Continental Divide. Gaillard Cut, forming the
passageway between the opposite slopes of the divide, is 7.97 miles long, 300 feet wide at
the bottom, and from 45 to 65 feet in depth. The great depth of the Cut is
responsible for the magnitude of the slides, which are breaks in the bans, due to the
pressure of the material. The elementary phenomena of slides are encountered in
almost any kind of cutting or trenching through earth; the great depth of the Gaillard cut
has caused similar breaks even in ordinarily firm rock. The slides are responsible
for 35,158,225 cubic yards of additional excavation to February 1, 1915, To that
date the total excavation from the Cut has been 117,077,044 cubic yards. The Cut is
an arm of Gatun Lake and its bottom is accordingly 40 feet above sea level.
At the south end of the cut, on the Pacific slope of the divide,the waters are held back
by Pedro Miguel Dam and Lock. The dam is of earth, protected by rock riprap at the
water levels, and is 1,400 feet long, extending from a high hill on the west to the lock,
which is set at the base of a high hill on the east.
Below Pedro Miguel Lock and Dam is a small lake, Miraflores Lake, through which the
channel passes to Miraflores Locks, which effect the transit between Miraflores Lake and
the Pacific entrance channel. the surface is normally 55 feet above sea level.
Its area is 1.88 square miles, and it may always be kept at full depth by supplying
water from Gatun Lake, as to fill it completely from Gatun Lake would lower the surface of
the latter less than 6 inches. The length of the canal channel through it is 1.4
miles. The lake is impounded by an earth dam 2,700 feet long, connecting with
Miraflores Locks from the west, and by a concrete spillway dam to the east of the locks,
500 feet long, on which are mounted eight regulating gates similar to those on the Gatun
Spillway.
The transits between the several levels of the canal -- between the Atlantic and Gatun
Lake, between Gatun Lake (Gaillard Cut) and Miraflores, and between Miraflores Lake and
the Pacific -- are effected by means of massive locks of concrete and gates of steel.
Three sets of locks were built -- one set in three successive levels at Gatun, a set with
one lift at Pedro Miguel, and set of two lifts at Miraflores. The differences in
levels overcome at the three places are, respectively, 85, 30 1/3, and 54 2/3 feet, the
latter varying according to the tide in the Pacific, figure given being for mean tide.
Each lock consists of two parallel chambers, which effect a double-tracking of the channel
and allow vessels going in opposite directions to use the same flight of locks
simultaneously. All the chambers have the same length, 1,000 feet, and width, 110
feet; the depth of water in the locks varies from approximately 81 feet when a boat is
being locked down and 45 feet when a boat is being locked up, and there is always a
minimum depth over the gate sill of 45 feet.
At the upper and lower ends of each set of locks the center wall was extended
approximately 1,250 feet to form a long pier, against which entering vessels can bring up
before entering the chambers of the locks proper; and the side walls were flared out at an
angle of 60º to form a funnel-shaped entrance. Both the center-approach walls and
the flare walls are fitted with strips of timbers resting on helical springs to form
buffers for the vessels, and the outer end of the center wall is fitted with a resilient
fender of heavy timbers.
The channels of the lock are blocked by massive steel gates which cut off the flow of
water and divide the locks into chambers. The flow of water into and from the
chambers is effected through culverts running longitudinally through the bottoms of the
side and center walls and feeding into the chambers through lateral culverts running under
the floors of the chambers and emptying upward. The culverts are controlled by
valves.
In all 92 leaves, forming 46 gates of two leaves each, are used in the three sets of
locks. Each leaf is 65 feet long, so that then two are swung together to form a
closed gate they meet in the center of the 110-foot width at an obtuse angle. The
leaves are so set that this junction always points upstream against the downward pressure
of the water; this pressure accordingly forces them firmly together and affords an element
of safety, since a gate can not be opened until the water on both sides has been
equalized. The leaves range from 47 to 82 feet in height, according to location, and
they weigh from 390 to 730 tons each. The 82-foot gates occur only at the lower end
of Miraflores Locks, where they are necessary on account of tidal conditions.
The leaves are hinged to anchorages in the walls and are swung back and forth like
ordinary gates. They are moved by machines driven by electric motors. In fact,
every piece of mechanism in the locks is actuated by electricity, and this has made
possible a central control by which an operator at a central switchboard can cause every
movement of the lock equipment except the running of the towing locomotives, which are
under the control of individual operators riding on them, and the handling of the
emergency dams.
[Editor's Note, 10/11/99: Madden Dam was built in the 1920s to supplement the
water supplied by Gatun Lake for all Canal operations. There was a severe drought a
couple of years ago which did threaten Canal operations. There are plans right now
for the immediate building of another dam. Approximately 8,500 families will be
displaced by the building of this dam.]
From The Official Handbook
of the Panama Canal, 1915
CZBrats
October 11, 1999
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