The Panama Canal. Frederic J. Haskin
earth dams in the world are located in California. The Contra Costa Water Company's dam at San Leandro is 120 feet high and not nearly so immense in its proportions as Gatun Dam, yet it weathered the San Francisco earthquake without difficulty. In Panama City there is an old flat arch that once was a part of a church. It looks as though one might throw it down with a golf stick, and yet it has stood there for several centuries. As a matter of fact, Panama is out of the line of earthquakes and volcanoes, but even if shocks much worse than those at San Francisco were to come, there is no reason to fear for the safety of the big structure.
The lack of knowledge of some of those who in years past criticized the Gatun Dam was illustrated by an amusing incident that occurred at a senatorial hearing on the Isthmus. Philander C. Knox, afterwards Secretary of State, was then a Senator and a member of the committee which went to the Isthmus. Another Senator in the party had grave doubts about the stability of Gatun Dam, and asked Colonel Goethals to explain how a dam could hold in check such an immense body of water. Colonel Goethals, in his usual lucid way, explained that it was because of that well-known principle of physics that the outward pressure of water is determined by its depth and not by its volume—that a column of water 10 feet high and a foot thick would have just as much outward pressure as a lake 200 square miles in extent and 10 feet deep. Still unconvinced, the Senator pressed his examination further. At this juncture Senator Knox, who is a past master at the art of answering a question with a question, interposed, and asked his colleague: "Senator, if your theory holds good, how is it that the dikes of Holland hold in check the Atlantic Ocean?"
CHAPTER IV
THE LOCKS
Ships that pass Panama way will climb up and down a titanic marine stairway, three steps up into Gatun Lake and three steps down again. These steps are the 12 huge locks in which will center the operating features of the Isthmian waterway. The building of these locks represents the greatest use of concrete ever undertaken. The amount used would be sufficient to build of concrete a row of six-room houses, reaching from New York to Norfolk, via Philadelphia, Baltimore, Washington and Richmond—houses enough to provide homes for a population as large as that of Indianapolis.
The total length of the locks and their accessories, including the guide walls, approximates 2 miles. The length of the six locks through which a ship passes on its voyage from one ocean to the other is a little less than 7,000 feet.
If one who has never seen a lock canal is to get a proper idea of what part the locks play in the Panama Canal, he must follow attentively while we make an imaginary journey through the canal on a ship that has just come down from New York. Approaching the Atlantic entrance from the north, we pass the end of the great man-made peninsula, jutting out 11,000 feet into the bay known as Toro Point Breakwater. It was built to protect the entrance of the canal, the harbor, and anchorages from the violent storms that sweep down from the north over that region. Omitting our stops for the payment of tolls, the securing of supplies, etc., we steam directly in through a great ditch 500 feet wide and 41 feet deep, which simply permits the ocean to come inland 7 miles to Gatun. When we arrive there we find that our chance to go farther is at an end unless we have some means of getting up into the beautiful lake whose surface is 85 feet above us. Here is where the locks come to our rescue. They will not only give us one lift, but three.
When we approach the locks we find a great central pier jutting out into the sea-level channel. If our navigating officers know their duty they will run up alongside of this guide wall and tie up to it. If they do not they will run the ship's nose into a giant chain, with links made of 3-inch iron, that is guaranteed to bring a 1,000-ton ship, going at the rate of 5 knots per hour, to a dead standstill in 70 feet. When we are once safely alongside the guide wall, four quiet, but powerful locomotives, run by electricity, come out and take charge of our ship. Two of them get before it to pull us forward, and two behind it to hold us back. Then the great chain, which effectively would have barred us from going into the locks under our own steam, or from colliding with the lock gates, is let down and we begin to move into the first lock.
Starting at the sea-level channel, the first, second, and third gates are opened and our ship towed into the first lock. Then the second and third gates are closed again, and the lock filled with water, by gravity, raising the ship at the rate of about 2 feet a minute, although, if there is a great rush of business, it may be filled at the rate of 3 feet a minute. When the water in this lock reaches the level of the water in the lock above, gates four and five are opened, and we are towed in. Then gate four is closed again, and water is let into this lock until it reaches the level of the third one. Gates six, seven, and eight are next opened, and we are towed into the upper lock. Gates six and seven are now closed, and the water allowed to fill the third lock until we are up to the level of Gatun Lake. Then gates nine and ten are opened, the emergency dam is swung from athwart the channel, if it happens to be in that position, the fender chain like the one encountered when we entered the first lock, and like the ones which protect gates seven and eight, is let down, the towing engines turn us loose, and we resume our journey, with 32 miles of clear sailing, until we reach Pedro Miguel. Here, by a reverse process, we are dropped down 301⁄3 feet. Then we go on to Miraflores, a mile and a half away, where we are lifted down 542⁄3 feet in two more lifts. This brings us back to sea level again, where we meet the waters of the Pacific, and steam out upon it through a channel 500 feet wide and 8 miles long.
Having learned something of the part the locks play in getting us across the Isthmus, by helping us up out of one ocean into Gatun Lake and then dropping down into the other ocean, it will be interesting to note something of the mechanism. A very good idea of how a lock looks may be gathered from the accompanying bird's-eye view of the model of Pedro Miguel Lock.
It will be seen that there are two of them side by side—twin locks, they are called, making them like a double-track railway. The lock on the right is nearly filled for an upward passage. The ship will be seen in it, held in position by the four towing engines, which appear only as tiny specks hitched to hawsers from the stem and stern. Behind the ship are the downstream gates. They were first opened to admit the ship, and then closed to impound the water that flows up through the bottom of the lock. Ahead are the upstream gates, closed also until the water in the lock is brought up to the level of the water in the lake. Then the gates will be opened, the big chain fender will be dropped down, and the ship will be towed out into the lake and turned loose. On the side wall of the right lock there is a big bridge set on a pivot so that it can be swung around across the lock and girders let down from it to serve as a foundation upon which to lay a steel dam if anything happens to the locks or gates. On the other lock the bridge has been swung into position, and the steel girders let down. Great steel sheets will be let down on live roller bearings on these girders, and when all are in place they will form a watertight dam of steel. Between this bridge and the reader is a huge floating tank of steel, which may be used to dam all the water out of the locks when that is desired.
Referring to the next figure we see a cross section of the twin locks. The side walls are from 45 to 50 feet thick at the floor. At a point 241⁄3 feet above the floor they begin to narrow by a series of 6-foot steps until they are 8 feet wide at the top. The middle wall is 60 feet wide all the way up, although at a point 421⁄2 feet above the lock floor room is made for a filling of earth and for a three-story tunnel, the top story being used as a passageway for the operators, the second story as a conduit for electric wires, and the lower story as a drainage system.