GATUN DAM AND LOCKS
Entering the Panama Canal from the Atlantic, one finds the beginning of
that section called by the engineers the Atlantic Division, four miles
out at sea in Limon Bay, a shallow arm of the Caribbean on the shore of
which are Colon and the American town of Cristobal. From its beginning,
marked only by the outermost of a double line of buoys, the canal
extends almost due south seven miles to the lowest of the Gatun Locks.
Of this distance four miles is a channel dredged out of the bottom of
Limon Bay and the bottom width of the canal from its beginning to the
locks is 500 feet. Its depth on this division will be 41 feet at mean
tide. For the protection of vessels entering the canal at the Atlantic
end, or lying in Colon harbor, a great breakwater 10,500 feet, or a few
feet less than two miles long, made of huge masses of rock blasted along
the line of the Canal, or especially quarried at Porto Bello, extends
from Toro Point to Colon light. In all it will contain 2,840,000 cubic
yards of rock and its estimated cost is $5,500,000.
In the original plans for the harbor of Cristobal a second breakwater
was proposed to extend at an angle to the guard one, but the success of
the former in breaking the force of the seas that are raised by the
fierce northers that blow between October and January has been so great
that this may never be needed. Its need is further obviated by the
construction of the great mole of stone and concrete which juts out from
the Cristobal shore for 3500 feet at right angles to the Canal. From
this mole five massive piers will extend into the harbor, jutting out
like fingers on a hand, each 1000 feet long and with the space between
them 300 feet wide so that two 1000 foot ships may dock at one time in
each slip. The new port of Cristobal starts out with pier facilities
which New York had not prepared for the reception of great ships like
the “Vaterland” and the “Aquitania” at the time of their launching.
[Illustration: ENTRANCE TO GATUN LOCKS
The rafts in the foreground carry pipes through which suction dredges
discharge material removed]
[Illustration: I. COLON: THESE PICTURES IN ORDER FORM A PANORAMA OF THE
COLON WATER FRONT]
[Illustration: II. COLON: PART OF THE RESIDENTIAL DISTRICT ON THE WATER
FRONT]
[Illustration: III. COLON: PANAMA RAILROAD AND ROYAL MAIL DOCKS]
[Illustration: IV. COLON: THE DE LESSEPS HOUSE IN THE DISTANCE SHOWS
LOCATION OF NEW DOCKS]
From the shore of the bay to the first Gatun lock is a little less than
four miles. The French dug a canal penetrating this section, a canal
which forms today part of our harbor and which has been used to some
extent for the transportation of material for the Gatun dam. Our
engineers however abandoned it as part of our permanent line, and it is
rapidly filling up or being over-grown by vegetation. At its best it was
about fifteen miles long, 15 feet deep as far as Gatun, and 7 feet deep
thence to the now vanished village of Bohio.
The Canal from the seaboard to the Gatun locks was straightaway
excavation, through land little higher than the water, with tidewater
following so that the work could be done by floating dredges. No novel
problems were presented to the engineer, nor are interesting
achievements displayed to the tourist until the great dam itself is
reached.
[Illustration: _Photo by Underwood & Underwood_
SOUTH APPROACH WALL, GATUN LOCKS]
The simplest way of reaching the Gatun dam is of course by train from
Colon, a ride of perhaps twenty minutes. But a more spectacular one is
by launch, either up the Canal, or around by the Chagres River from its
mouth. The latter is a difficult trip however and seldom essayed. One
advantage of taking the Canal is that it gives a much clearer idea of
the construction of the dam than can be derived by approaching it by
railroad. The first significant fact forced upon your attention in thus
coming upon the dam is that it does not look like a dam at all, but
rather like a long and gently sloping hill pierced at one point by a
sort of masonry gate which upon closer approach reveals itself as a
system of mighty locks.
[Illustration: GATUN LOCKS OPENING INTO THE LAKE
The skeleton structure on the left is the frame-work of the emergency
dam which swings directly athwart the lock]
Not very long ago there was a wide-spread apprehension in the United
States, bred of a rather shallow newspaper criticism very widely
republished, that the Gatun dam would prove inadequate to the pressure
of the waters impounded behind it and might collapse, or “topple over”.
If all who have been impressed by that gruesome prophecy could see the
dam itself their apprehensions would be speedily quieted. One might as
well talk of toppling over the pyramids, or Murray Hill, New York (not
the structures on it, but the hill itself) or the Treasury Building at
Washington. Elevations, natural or artificial, the base of which is
eight to ten times their height, cannot topple over while the force of
gravity continues to operate. Now the height of Gatun dam is 105 feet,
and from its crest the filling of clay and rock slopes gently away on
the landward side for nearly half a mile. There are more abrupt
eminences on many of our rolling prairies. The face on the lake side
descends somewhat more abruptly, but is still several hundred feet long
before its slope ends with the bed of the lake. This face is covered
with broken stone down to the “toe”--as they call the walls of rough
rock between which the dirt dam was built.
[Illustration: _Photo by Thompson_
GATUN LAKE SEEN FROM THE DAM]
[Illustration: _Copyright, 1911, by Munn & Co. Inc. From Scientific
American_
BIRD’S EYE VIEW OF GATUN DAM
In the foreground the locks, only two of the three steps being fully
shown. In the middle distance the spillway, through which surplus water
flows into the Chagres and old French Canal]
The method of building the dam was simple enough even though it sounds
complicated in the telling. When Congress acquiesced in the minority
report of the Board of International Engineers, approved by the
President and recommending a lock type canal, it meant that instead of
simply digging a ditch across the Isthmus we would create a great
artificial lake 85 feet above sea level, confined by dams at either
ends, with locks and two short canals to give communication with the
oceans. To create this lake it was determined to impound the waters of
the Chagres, and a site near the village of Gatun, through which the old
French canal passed, was selected for this purpose. Conditions of
topography of course determined this site. The Chagres valley here is
7,920 feet wide, but the determining fact was that about the center of
the valley was a hill of rock which afforded solid foundation for a
concrete dam for the spillway. Geologists assert that at one time the
floor of the valley was 300 feet higher than now, and that in the ages
the Chagres River cut away the shallow gorges on either side of the
rocky hill. These, it was determined, could readily be obstructed by a
broad earth dam of the type determined upon, but for the spillway with
its powerhouse and flood gates a rock foundation was essential and this
was furnished by the island.
[Illustration: _Photo by Underwood & Underwood_
CONSTRUCTION WORK ON GATUN DAM
The space between two rock walls has been filled with mud, which having
hardened, supports dirt trains bringing spoil from Culebra Cut to build
up the dam to required dimensions]
[Illustration: _Photo by Underwood & Underwood_
PUMPING MUD INTO THE CORE OF GATUN DAM]
The first step in the construction of the dam was to dam the Chagres
then flowing through its old channel near the site chosen for the
spillway, and through the old French canal. This was accomplished by
building parallel walls, or “toes” of broken stone and filling the space
between with fluid mud pumped from the old channel of the stream. A new
channel of course was provided called the “west diversion”. The toes are
about a quarter of a mile apart and rise about 30 feet high. They were
built by the customary devices of building trestles on which dump trains
bearing the material were run. After the core of fluid silt pumped in
between the walls had begun to harden, dry earth was piled upon it,
compressing it and squeezing out the remaining moisture. As this surface
became durable the railroad tracks were shifted to it, and when I
visited the dam in 1913 the made land of the dam was undistinguishable
from the natural ground surrounding it. Over it scores of locomotives
were speeding, dragging ponderous trains heavy laden with “spoil” from
the Culebra Cut. From the crest on the one hand the dam sloped away in a
gentle declivity nearly half a mile long to the original jungle on the
one side, and a lesser distance on the other, to the waters of the Gatun
Lake then less than half filled. When the main body of the dam had
been completed and the spillway was ready to carry off the waters of the
Chagres then flowing through the “west diversion” the task of damming
the latter was begun. This was the first effort to stem the current of
the Chagres, the river dreaded for so many reasons, and the description
by Lieutenant Colonel William L. Sibert, the engineer in charge of this
division, will be of interest:
[Illustration: COPYRIGHT, 1913, BY F. E. WRIGHT
A NATIVE BAKERY
The Panamanian never does anything indoors that he can do in the open.
The village bakery, the village mortar or mill and the village laundry
are social meeting places used by all.]
[Illustration: GATUN UPPER LOCK]
[Illustration]
[Illustration: _Photo by Underwood and Underwood_
CENTER: GATUN CENTER LIGHT; LOWER CORNER: EMERGENCY GATES]
“The elevation of the spillway channel is 10 feet above sea level,
consequently in any attempt to stop the flow of the Chagres and force it
through this channel, a rise of about 14 feet of water had to be
encountered. The banks and bottom of the west diversion were soft clay.
The plan adopted was to drive trestles across this channel on the
30-foot contour on each face of the dam, and to build, by dumping rock
directly into the stream, two dams at the same time, hoping to
distribute on such dams the head formed during construction. An
unlimited amount of waste rock was available for this work. The banks of
the channels were first made secure by dumping rock at the end of the
trestles. After the channel was contracted to some extent, a
considerable current developed; rock dumped from the trestles was
carried some distance down stream, forming a rock apron in the bed of
the stream below the dam. Quite deep holes, however, were dug by the
water below this rock apron. When the work on the two dams had
progressed so that a channel about 80 feet wide and 6 feet deep was left
in the center, it was found impracticable to make any headway. Stone
dumped from the trestles would be rolled down stream. The rainy season
was then about to commence. The lower part of the bents of the trestles
being well supported with rock, it was then decided to dump a carload or
two of crooked rails above the trestles in such a way that they would
form an entanglement and stop the rock, thus insuring either the
construction of the dam or the taking out of the trestle. By this means
the two dams were finally completed and the Chagres River successfully
diverted.”
[Illustration: _Photo by Underwood & Underwood_
SPILLWAY UNDER CONSTRUCTION
Concrete is dumped directly from the railway into the moulds. Pipes to
the power house are shown]
To the unprofessional observer the Gatun dam is a disappointment as a
spectacle. It does not look like a dam at all, but merely like a
continuation of one of the hills it connects. But as a matter of fact it
is the greatest dam in the world--a mile and a half long, 105 feet high,
half a mile thick at its base, 398 feet at the surface of the lake and
100 feet wide at the top. It is longer and higher than the Assouan dam
which the British built across the Nile though the latter, being all of
masonry, is vastly the more picturesque. Into the entire work will go
about 21,000,000 cubic yards of material.
One day while the Gatun dam was in the earlier stages of its
construction in 1908, a newspaper correspondent was temporarily detained
at Gatun while crossing the Isthmus. Idly, to pass the time away, he
strolled out on the dam to where he saw a group of men gathered. He
found them discussing a small break at the edge of the dam upstream; a
break not caused by any pressure of the water, for the water had not
reached that point, but by the weight of the heavy superstructure
pressing upon the semi-fluid core of the dam which then had not had
sufficient time for drainage and drying. The dispatch which the
correspondent sent north as the result of his casual observation of the
slide, was seized upon by the advocates of the sea-level canal as a text
from which to argue the entire impracticability of the lake-level
project. The agitation became so general and so menacing that President
Roosevelt was impelled to appoint a commission of seven engineers of
high professional standing and technical knowledge of dam building to
visit the spot and report upon the menace. Their verdict was that the
Canal engineers had gone far beyond the necessary point in making the
dam ponderous and safe. Secretary of War Taft, who happened to be on the
Isthmus when the break occurred, declared that it was “insignificant
when one takes into consideration the whole size of the dam”.
When the tricky Chagres gets on one of its rainy season rages the
spillway by which the dam is pierced at about its center will be one of
the spectacular points on the Canal line. That river drains a basin
covering 1,320 square miles, and upon which the rains in their season
fall with a persistence and continuity known in hardly any other corner
of the earth. The Chagres has been known to rise as much as 40 feet in
24 hours, and though even this great flood will be measurably lowered by
being distributed over the 164 square miles in Gatun Lake, yet some
system of controlling it by outlets and flood gates was of course
essential to the working and the safety of the Canal. The spillway is
the center of this system, the point at which is the machinery by which
the surface of Gatun Lake can be at all times kept within two feet of
its normal level, which is 85 feet above the level of the sea.
[Illustration: PARTLY COMPLETED SPILLWAY, 1913
The river was low when this picture was taken. At high water it will
flow over the completed structure shown at the right]
Fundamentally the spillway is a channel 1,200 feet long and 285 feet
wide cut through the solid rock of the island which at this point
bisects the now obliterated Chagres Valley. Though cut through rock it
is smoothly lined and floored with cement; closed at its upper end by a
dam, shaped like the arc of a circle so that, while it bars an opening
of only 285 feet, its length is 808 feet. For the benefit of the
unprofessional observer it may be noted that by thus curving a dam in
the direction of the force employed against it, its resisting power is
increased. It resists force exerted horizontally precisely as an arch
resists force, or weight, exerted from above. The dam at the spillway
extends solidly across the opening to a height of 69 feet. But this is
16 feet below the normal level of the Lake. From the top of the solid
dam rise thirteen concrete piers to a height as planned, of 115 feet
above sea level, that is the piers will rise 46 feet above the top of
the dam. Between each two of these piers will be mounted regulating
gates of steel sheathing, made water tight and movable up or down as the
state of the Chagres level requires a free or a restricted passage for
the water. Nor will those operating the gates await the visual
appearance of the flood before throwing wide the passage for its onrush.
At divers points along the Chagres, and throughout its water shed are
little stations whence observers telephone at regular intervals
throughout the day to the office at the spillway the result of their
observations of the river’s height. With these figures at hand the
controller of the gates can foresee the coming of a flood hours before
it begins to beat against the gates.
[Illustration: _Photo by Underwood & Underwood_
THE GIANT PENSTOCKS OF THE SPILLWAY]
[Illustration: THE SPILLWAY AT HIGH WATER
A comparison with the picture on page 179 will show the varying stages
of the river]
[Illustration: _Photo by Underwood & Underwood_
LOCK GATES APPROACHING COMPLETION]
The spillway further serves a useful and an essential purpose in that it
harnesses the water power of the useful Chagres, and turns it into
electric power to open and shut the colossal gates of the various locks;
to propel the electric locomotives that tow the great ships through the
concrete channels; to light the canal towns and villages, and the
lighthouses on the line; to run the great cranes at Balboa and
Cristobal; to run the machinery in the shops at Balboa; to furnish
motive power, if so determined for the Panama Railroad, and to swing the
great guns at Toro Point and Naos Island until their muzzles bear with
calm yet frightful menace upon any enemy approaching from either the
Caribbean or the Pacific. There will be power for all these functions,
and power too to light Panama and Colon, to run the Panama tramway and
perform other useful functions if the present grip of private Panama
monopoly upon these public services shall be relinquished. The water
drops 75 feet through huge penstocks to great turbines in the spillway
hydro-electric station with a capacity of 6,000 kilowatts, but the
amount of water power is sufficient for double that current, and
turbines to supply the addition can be installed whenever the need for
the power develops.
[Illustration: THE WATER KNOCKING AT GATUN GATES]
[Illustration: WALL OF GATUN LOCK SHOWING ARCHED CONSTRUCTION]
The Gatun locks are built at the very eastern end of Gatun dam, at the
point where it joins the mainland bordering the Chagres valley. Of their
superficial dimensions I have already spoken, and have described their
appearance as seen from the deck of a ship in passage. It will be hard
however for one who has not stood on the concrete floor of one of these
massive chambers and looked upward to their crest, or walking out on one
of the massive gates peered down into their depths, to appreciate their
full size. It is all very well to say that the “Imperator,” the greatest
of ships now afloat, could find room in one of these locks with five
feet at each side, and fifty feet at each end to spare, but then few of
us have seen the Imperator and nobody has seen her in the lock. It is
all very well to figure that a six story house would not rise above the
coping of one of these locks, but imagination does not visualize the
house there, and moreover there are stories and stories in height. Yet
as one stood on the floor of one of these great monolithic tanks as they
were being rushed to completion in 1913, and saw locomotives dwarfed by
the ponderous walls betwixt which they plied, and whole trains of loaded
dump cars swallowed up in a single lock chamber, one got some idea of
the magnitude of the work. A track for a travelling crane extended down
the center of the chamber and the monster rumbled back and forth
carrying loads of material to their appointed destinations. Across the
whole width of the Canal below the locks stretched cable carriers upheld
by skeleton devices of steel mounted on rails so that the pair of them,
though separated by 500 feet of space, spanned by the sagging cables,
could be moved in unison. Out on the swinging cables ran the loaded cars
or buckets, filled with concrete and dumped with a crash and a roar at
the chosen place. Giant mixers ground up rock from Porto Bello, sand
from Nombre de Dios, and cement from divers states of our union into a
sort of Brobdignagian porridge with which the hungry maws of the moulds
were ceaselessly fed. Men wig-wagged signals with flags across gaping
chasms. Steam whistles blew shrill warnings and cryptic orders. Wheels
rumbled. Pulleys creaked. It seemed that everything a man could do was
being done by machine, yet there was an army of men directing,
correcting and supplementing the mechanical labor.
[Illustration: _Photo by Underwood & Underwood_
TRAVELLING CRANES AT WORK
Mounted on rails these cranes carry the heaviest burdens. Those shown
are placed for delivering concrete to the forms. One crane will cost
$60,000]
Into the locks at Gatun will go 2,000,000 cubic yards of concrete if the
original estimate is adhered to. A statistician estimates that it would
build a wall 8 feet wide and 12 feet high and 133 miles long--which
would just about wall off the state of Delaware from the rest of the
Union.
The side walls of each of the locks are practically monoliths,
constructed of concrete poured into great steel frames or moulds where
it hardens into a solid mass. They are based in the main on bed rock,
though it was found on making tests that the bed rock was not of
sufficient extent to support the guide walls as well, so one of these is
therefore made cellular to lighten its weight, which rests on piles of
60 feet long capped and surrounded with concrete. This wall was built by
slow stages and allowed to stand in order that its settlement might be
uniform. An examination of the picture below will make clear the method
of constructing the lock walls, for in it are shown the completed
monoliths and a steel form half completed with men preparing it for the
concrete therein. Col. Sibert describes the details of the work thus:
“The locks proper are founded on rock and the heavy masonry is
completed. This rock foundation was not of sufficient extent, however,
at available elevations, for supporting the guide walls. Under that
guide wall extending into the lake the underlying rock at the south end
is about 150 feet below sea level, and the overlying material is soft.
This wall is cellular in construction. It is composed of four
longitudinal walls about 2 feet thick with cross walls about 17 feet
apart, all built of reinforced concrete.
[Illustration: _Photo by Underwood & Underwood_
BUILDING A MONOLITH]
“The natural ground underlying the wall was about 8 feet above sea
level. On this ground a wide fill with a very flat slope was constructed
to elevation plus 35, and through this piles about 60 feet long, 4-foot
centers, were driven and a heavy reinforced concrete slab built around
the heads of the piles, on which was erected the cellular structure.
There was a continual slow settlement of this wall as its construction
progressed. It was brought to a height of 61 feet above sea level
through its entire length in order that the settlement might extend over
the whole base before any part was brought to full height.
[Illustration: A CULVERT IN THE LOCK WALL]
“The north guide and flare walls are yet to be built. It will be
necessary to go to a depth of about 70 feet below sea level through very
soft material in order to uncover the rock on which to build the flare
walls. Under the guide wall itself the rock is at a still lower
elevation, and a pile foundation will probably be constructed, the
piling going to rock. The material in this space was too soft to hold up
steam shovels, and it was decided to do the general excavation by
suction dredges. These dredges cut their way into the space where the
walls in question are to be built, making a channel just wide and deep
enough for their passage. They then widened out the cut and deepened it
to 41 feet below sea level. An earthen dam was then built across the
narrow entrance cut, shutting off the connection with the sea, and as
the dredges worked they were lowered. They are now floating at an
elevation of 32 feet below sea level and can remove the material to the
depth required. After the excavation is completed it is proposed to have
the dredges excavate a sump 65 feet below sea level and lower the water
to 50 feet below sea level in order to test the stability of the sides
of the cut. If there is no sliding the pit will be filled with water;
the dredges floated out; the dam across the entrance channel replaced
and the excavation unwatered for the construction of the walls first
referred to.
[Illustration: DIAGRAM OF LOCK-GATE MACHINERY]
[Illustration: TOWING LOCOMOTIVE CLIMBING TO UPPER LOCK]
“The masonry of the Gatun locks was largely placed by cableways, having
a span of 800 feet, covering the entire space to be occupied by the
locks. The stone and sand for the concrete were obtained, respectively,
20 and 40 miles down the Caribbean coast, and were brought in barges up
the old French Canal as closely as possible to the lock site, and were
unloaded by cableways into large stock piles near the bank. The
material, however, was still 3,500 feet away and 60 feet below the
center of lock construction. This situation caused the adoption of a
central mixing plant near the central portion of the locks, consisting
of eight 2-yard mixers. An automatic, electric, loop-line railroad, each
car carrying the material for a batch of concrete, was installed,
passing under the cement shed, under the sand and stone piles; and over
the mixers. The mixed concrete was delivered to the cableways requiring
it by an electric line, the flat cars of which were handled by electric
locomotives. Steel forms were used in constructing the walls of the
locks”.
A vital feature of the locks is, of course, getting the water into and
out of them, and the method of operating the gigantic gates. The former
is simple enough of explanation, though the _modus operandi_ will be
entirely concealed when the locks are in operation. Through each of the
side walls, and through the center walls which divide the pairs of
locks, runs a tunnel 18 feet in diameter. To put it more graphically a
tunnel large enough to take a mogul locomotive of the highest type. From
this main tunnel smaller ones branch off to the floors of the locks that
are to be served, and these smaller chutes are big enough for the
passage of a farmer’s wagon with a span of horses. These smaller chutes
extend under the floor of the lock and connect with it by valved
openings, the valves being operated by electricity. There is no pumping
of the water. Each lock is filled by the natural descent of the water
from the lock above or from the lake. By the use of the great culvert in
the central wall the water can be transferred from a lock on the west
side of the flight to one on the east, or vice versa. Though it hardly
seems necessary, every possible device for the conservation of the water
supply has been provided.
We will suppose a vessel from the Atlantic reaches Gatun and begins to
climb to the lake above. The electric locomotives tow her into the first
lock, which is filled just to the level of the Canal. The great gates
close behind her.
[Illustration: THE HEAVY WHEEL SHOWN IS THE “BULL WHEEL”
By its revolution it thrusts or withdraws the arm at the right which
moves the gate]
How do they close? What unseen power forces those huge gates of steel,
shut against the dogged resistance of the water? They are 7 feet thick,
65 feet long and from 47 to 82 feet high. They weigh from 390 to 730
tons each. Add to this weight the resistance of the water and it becomes
evident that large power is needed to operate them. At Gatun in the
passing of a large ship through the locks, it will be necessary to lower
four fender chains, operate six pairs of miter gates and force them to
miter, open and close eight pairs of rising stem gate valves for the
main supply culverts, and thirty cylindrical valves. In all, no less
than 98 motors will be set in motion twice during each lockage of a
single ship, and this number may be increased to 143, dependent upon the
previous position of the gates, valves and other devices. Down under the
surface of the lock wall, packed into a little crypt which seems barely
to afford room for its revolving, is a great cogwheel 20 feet in
diameter, revolving slowly and operating a ponderous steel arm which
thrusts out or pulls back the gate as desired. The bull wheel, they call
it, is driven by a 27 horse power motor, while a smaller motor of 7¹⁄₂
horse power locks the gates tight after they are once in position. Two
of these bull wheels, and two each of the motors are needed for each
pair of gates.
[Illustration: THE TANGLED MAZE OF STEEL SKELETONS THAT ARE A LOCK IN
THE MAKING]
The ship then is in the lowest lock, one pair of gates closed tightly
behind her. Another pair confronts her holding back the water in the
lock above, which if filled, will be just 28¹⁄₃ feet above the surface
of that on which she floats. But the water about her is now slowly
rising. Another set of electric motors concealed in the concrete wall
have set in motion the valves in the floor of the lock, and the water is
flowing in from the tunnels, raising the ship and at the same time
lowering the water in the lock above. When the vessel’s keel is higher
than the sill of the lock above the upper gates swing slowly back and
fold in flat with the wall. The ship is now in a chamber 2000 feet long
filled to a level. The locomotives pull her forward a thousand feet or
so. Again great gates close behind her. Again the water rises slowly
about her lifting her with it. The first process is repeated and she
enters the third lock. By the time she has been drawn out into the lake
and the locomotives have cast her off, more than 100 electric motors
with a horse power ranging from 7¹⁄₂ to 50 each will have contributed to
her progress. Altogether over 1000 individual motors will be required
for the different locks. Indeed the whole interior of those massive lock
walls is penetrated by lighted galleries strung with insulated wires
bearing a death-dealing current. Men will be stationed at the various
machinery rooms, but the whole line of machinery can be operated from a
central operating tower on the lock above.