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.