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one lock into the next. The three locks are in duplicate; that is, a vessel may go up either one flight or the other of the duplicate locks, or one flight may be used for ascending vessels and the other for descending vessels. The corresponding locks adjoin and there is only a dividing wall between them. After the ship has passed into the lower lock, and while it is being raised, the following ship, if close behind, may be tied up at the approach wall 1200 feet long, formed by an extension of the dividing wall. Each lock has a net or usable length of 1000 feet, and a net or usable width of 110 feet, but the dimensions of the ship must be somewhat less than this to provide for fenders and clearances.

The formation of the lake with the water 85 feet above the sea level obviated all digging for 17 miles, except the top of an occasional mound. (See plan No. 5.) The alignment of the channel in the lake was determined by the position of hills, changed into islands by the rising water.

At the locks, the canal axis makes a slight bend to the left and the channel of 1000 feet width and 75 feet depth extends in a straight line for 31 miles to the first bend in the lake. This bend is followed by a straight channel of the same width but reduced depth for a distance of 41 miles, almost to Bohio, where a further turn to the left is made. The course does not run straight to Bohio from the locks, because Tiger Hill and Lion Hill are in the way. After a two-mile run from Bohio to Buena Vista, 1000 feet wide, there is a turn to the right, the course continuing straight for a distance of 24 miles to a point opposite Frijoles.

Here there is a further turn to the right, with a straight course of 21 miles, still 1000 feet wide, to a point near Tabernilla; then a turn to the left, with a reduction in width to 800 feet, and a straight reach of 3 miles to a point near San Pablo. The lake has now become a narrow arm, occupying the region where the valley of the Chagres had much steeper banks. At San Pablo there is a turn to the left with a short run 800 feet wide of 1 mile; then a turn to the right, another short run of 1 mile, with a further turn to the right; then a longer reach of 3 miles, with width reduced to 500 feet, passing the submerged town of Gorgona; then a right turn and a 1-mile run to a point near Gamboa. From Gatun to Gamboa there are 23 crossings of the former course of the Chagres, showing that the canal has practically followed the course of the river, but with the aid of steam shovels has selected a much straighter course than the one carved by the river along the lines of least resistance.

At Bas Obispo, which is close to Gamboa, we enter the great Culebra Cut. The minimum width of the canal up to this point has been 500 feet, but through the following 8.1 miles the bottom width is reduced to 300 feet to save excavation. A width of only 200 feet was originally contemplated but was wisely increased to 300 feet. The banks of the canal become higher and higher as we pass on, until at Gold Hill, the elevation of the highest land on one side is 554 feet above sea level, and the other side, 410 feet, while the land over the center of the canal was formerly 312 feet above sea level, or 227 feet above the bottom of the canal. The minimum depth of the canal on the entire upper section is 45 feet at normal lake level, or 40 feet at low lake level, but throughout Gatun Lake the depth is in excess of these. The Culebra Cut and the 85-foot elevation of the water both end at the Pedro. Miguel Lock. In passing through the cut, from Bas Obispo to Pedro Miguel, there are eight straight reaches connected by easy curves, three to the right and four to the left. It is most remarkable that so large a portion of this run is on straight lines, and that the total degree of curvature has been kept so low.

At Pedro Miguel there is one lock in duplicate which lowers the vessel to the 55-foot elevation of Miraflores Lake. The Pedro Miguel Lock has approach walls formed by 1200-foot extensions in both directions of the dividing-wall between the locks. Miraflores Lake is comparatively small, and a run of 11 miles, in a 500-foot channel 45 feet deep, takes the ship to Miraflores. At this point there are two locks in duplicate, with approach walls at the upper and lower levels, the same as at Pedro Miguel and Gatun. The two locks at Miraflores lower the vessel to tidewater, a drop of 45 feet at high tide, or 65 feet at low tide. (See plan No. 3.) The 20-foot tides on the Pacific coast have made the problem more difficult than on the Atlantic coast, where the tide is only 2 feet. One-half mile beyond Miraflores Locks, the canal makes a turn to the right and extends for a distance of 21 miles to Balboa, where it makes a turn to the left and extends for 41 miles to deep water in the Bay of Panama. The Pacific sea-level section is all of 500 feet width,

and the depth of the water is 55 feet at high tide and 35 feet at low tide, and is usually stated to be 45 feet deep, referring to mean tide.

The total length of the canal, measured along its axis, is 50.4 miles. The portion within the shore lines is only 41.5 miles, and the remainder consists of dredged channels in Limon Bay and Panama Bay. Of the total length, 144 miles are at sea level, over 231 miles in Gatun Lake, nearly 3 miles in the locks or alongside approach walls, 14 miles in Miraflores Lake and 8 miles in the Culebra Cut. In the total length there are 22 bends, with a total curvature of 600 degrees and 51 minutes. The average length of the straight reach is a little over 2 miles. At each bend the canal is widened by cutting away on the inside of the bend, the shape and amount of cutting having been determined after observations of vessels actually rounding turns.

The time required for a vessel to pass through was estimated to be from 10 to 12 hours, of which 3 hours are required for passing the locks, and these estimates have been verified by experience. Through the Culebra Cut the vessel must reduce speed, but for most of the remaining distance may approach full speed.

GATUN LAKE

Less attention, it is believed, has been paid to Gatun Lake by those describing the canal than the subject really deserves. (See plan No. 1.) It forms the preponderant element in the American project. The great dam at Gatun, the spillway, and the locks are

[graphic]

Fig. 9. — Gatun upper locks, looking south from range light, showing Gatun Lake partly filled in the background. Other range light

on approach wall. Note steel lock gates in place and emergency dams on side walls ready to swing over the lock.

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