These are the third and last set of locks for a ship proceeding from the Atlantic to the Pacific. They are in two steps, or, to use the more technical expression, "two in flight," and they drop the vessel from the Miraflores Lake at 55 feet elevation down to sea-level. It must be noticed, however, that the fluctuations in the tide of the Pacific end are about 20 feet, and that the height of the lake is given for mean tide. In other words low water during "spring" tides is 10 feet below the average sea-level. The maximum lift for these locks therefore will be 65 feet. There are two dams holding up the waters of the Miraflores Lake, one to the west of earth, and one to the east of concrete. The former is 2,300 feet long and 40 feet wide at the top. The average "head" to which it is subjected is 30 feet, the maximum 40. Its construction is similar to that at Gatun. The concrete dam is about 500 feet long, and is provided with regulating works similar to and of the same dimensions as those at Gatun, the crest in this instance being 39 feet above mean tide-level, with seven openings, allowing a discharge of 7,500 cubic feet per second. The locks themselves will require 1,312,000 cubic feet of concrete. I should add that these dams at Pedro Miguel and Miraflores are, unlike their big brother at Gatun, founded upon the solid bedrock. There has, therefore, been no question as to their permanence and stability. Moreover, as will have been noticed, the pressure of water is only about a half of that at Gatun.
The relaying of most of the old Panama railroad was proceeding pari passu with the construction of the canal. Two sections of the old line, one from Colon to Mindi at the Atlantic end, the other from Corozal to Panama at the Pacific end, could be used for the new. All the rest had to be built. The greater portion of the old track was, indeed, submerged beneath the waters of Lake Gatun. The line is also being doubled throughout almost its entire length. It was originally intended to carry the line through the Culebra Cut along a berm 10 feet above the water surface, to be left for this purpose during the excavations of the channel; but the "slides" interfered with this project, and a new line to the east of the Cut was selected. The heavy embankments along the railway were among the most useful and convenient "dumps" for the material taken out of the Culebra cutting. As a great part of the railroad passes through the lake, culverts of reinforced concrete are provided to equalize the water on both sides of the embankments. South of Miraflores the new railway passes through a tunnel 800 feet long, and a striking feature of the canal is a steel bridge across the Chagres River near Gamboa, almost a quarter of a mile long. We need not dwell on the excavations of the tidal stretches of the canal on the Atlantic and Pacific ends or through Lake Gatun. A good deal of the French work was available at the tidal levels, but a vast amount of excavation had still to be done by steam-shovels as well as dredges, rocky elevations being found in both channels. Below the Miraflores locks a million and a half cubic yards of rock had to be removed. There will be some tidal current at the Pacific end, but as the sea-level section here will be 500 feet wide, the current will never run faster than about one foot per second. The sea is practically tideless at the Atlantic terminal, the variation being only 2.5 as a maximum, whereas at the Pacific it is 21.1.
CHAPTER XIV
THE COMPLETED CANAL.
We may now begin to consider the canal as a whole and in its completed state. From deep water in Limon Bay, 41-foot depth at mean tide, to deep water outside Panama, 45-foot depth at mean tide, is just about 50 miles. The greater part of the canal is at high elevation, only 15 miles of it being at sea-level. We shall note the varying depths and widths of the channel when we take our imaginary journey along it. Here it is enough to say that the minimum width will be 300 feet, the minimum depth 41 feet, the breadth and depth being, however, for the greater portion of its course, greater than these dimensions. Its highest point above sea-level, as the reader already knows, is 85 feet—that is, 85 feet at the surface of the water, and 40 feet at the canal bottom. The depth along this stretch is therefore 45 feet. The Panama Canal, though not so long as the Kiel and Suez Canals, is very much broader and deeper. Suez is 108 feet wide and 31 feet deep as minima; Kiel, 72 feet and 29½ feet. The Manchester Ship Canal is 120 feet by 26 feet. In length Panama, with its 50 miles, comes third, Suez being 90, Kiel 61, and Manchester 35½ miles long.
During the building of the canal the department of construction and engineering was arranged in three divisions—the Atlantic, embracing the engineering construction from deep water in the Caribbean Sea to include the Gatun locks and dam; the central division, extending from Gatun to Pedro Miguel; and the Pacific division, from Pedro Miguel to deep water in the Pacific Ocean. For the ordinary student, however, the channel divides naturally into four sections, the Atlantic level, the lake, the cutting, and the Pacific section (in two levels separated by locks).
The invisible channel of the waterway begins at the mouth of Limon Bay, about eight miles from Gatun locks. Limon, also known as Colon or Navy Bay, is about three miles wide and three and a half miles long from north to south. It is shallow, from three to seven fathoms deep, and seems to be steadily growing shallower. This is not surprising, as it is fully exposed to the "northers," which blow with terrific force from the Caribbean, and no doubt carry into the bay a good deal of detritus from the bottom of the sea. The heavy rains of the isthmus must also scour the land perpetually down into the bay. On the east side of the bay is the flat Manzanillo Island, a mile long by three-quarters broad, on which stands the city of Colon. This town, which was once known as Aspinwall, owes its existence to the Panama Railway, of which it is the northern or Caribbean terminus. Its position on the railway gave it an advantage over the old town of Chagres, a little distance along the coast to the west, which, though once a flourishing port, has now fallen on evil days. Near Colon is Cristobal, the new Atlantic terminal of the canal.