CHAPTER X
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.
ENTRANCE TO GATUN LOCKS
The rafts in the foreground carry pipes through which suction dredges discharge material removed
I. COLON: THESE PICTURES IN ORDER FORM A PANORAMA OF THE COLON WATER FRONT
II. COLON: PART OF THE RESIDENTIAL DISTRICT ON THE WATER FRONT
III. COLON: PANAMA RAILROAD AND ROYAL MAIL DOCKS
IV. COLON: THE DE LESSEPS HOUSE IN THE DISTANCE SHOWS LOCATION OF NEW DOCKS
Complete panorama (1 MB)
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.
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.
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.
Photo by Thompson
GATUN LAKE SEEN FROM THE DAM
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.
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
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:
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.
GATUN UPPER LOCK
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.”
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.
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.
Photo by Underwood & Underwood
THE GIANT PENSTOCKS OF THE SPILLWAY
THE SPILLWAY AT HIGH WATER
A comparison with the picture on page 179 will show the varying stages of the river
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.
THE WATER KNOCKING AT GATUN GATES
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.
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.
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.
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.
DIAGRAM OF LOCK-GATE MACHINERY
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.
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.
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.