How the Canal Works
In substance the Canal works consist, first, of an enormous dam (at Gatun), which holds up the water of the river Chagres so as to flood a valley twenty-four miles long; secondly, of a channel nine miles in length (the Culebra Cut) which carries the valley on through a range of low hills; and, thirdly, of a set of locks at each end of this stretch of water that are connected by comparatively short approaches with the sea. The surface of the lake is 79 to 85 feet above sea-level, and vessels will be raised to this height and lowered again by passing through a flight of three locks upward and another flight of three locks downward.
The area of the lake of impounded water will be 164 square miles, and it was doubted whether the damming of so large a mass of water, to a height of 85 feet, could safely be undertaken. But this portion of Central America is apparently not liable to earthquakes. And the dam is so large as to be a feature of the earth’s surface. It is nearly half a mile broad across its base, so that although its crest is 105 feet above sea-level its slope is not very perceptible. Its core is formed of a mixture of sand and clay, poured in from above by hydraulic processes. This has set hard, and is believed to be quite impervious to water at a much higher pressure than that to which it will be subjected. In the center of the river valley–a mile and a half broad–across which the dam has been flung, there very fortunately arose a low rocky hill. This is included in the dam, and across its summit has been constructed the escape or spill-way. During seasons of heavy rain the surplus discharge of river water is very heavy, and a cataract will pour over the spill-way. But it will rush across a bed of rock, and will be unable to erode its channel.
The locks are gigantic constructions of concrete. Standing within them one is impressed as by the mass of the Pyramids. The gates are hollow structures of steel, 7 feet thick. Their lower portions are water-tight, so that their buoyancy in the water will relieve the stress upon the bearings which hinge them to the lock-wall. Along the top of each lock-wall there runs an electric railway; small electric locomotives are coupled to a vessel as it enters the lock approach, and tow it to its place. Most vessels do not travel through the canal under their own power. This lessens the risk of its getting out of hand and ramming the lock-gate, an accident which has occurred on the big locks that connect Lake Superior with Lake Huron. So catastrophic would be such a mishap, releasing as it might this immense accumulation of water, that it seemed desirable at whatever expense to provide additional safeguards against it. There are in the first place cross-chains, tightening under pressure, which may be drawn across the bows of a ship that threatens to become unmanageable. Secondly, the lock-gates are doubled at the entrance to all the locks, and at the lower end of the upper lock in each flight. And, thirdly, each flight of locks can be cut off from the lake by an “emergency dam” of peculiar construction. It is essentially a skeleton gate, which ordinarily lies uplifted along the top of the lock-wall, but can be swung across, lowered, and gradually closed against the water by letting down panels. In its ordinary position it lies high above the masonry–conspicuous from some distance out at sea as a large cantilever bridge, swung in air.