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suction-dredge, also made in the United States. Inside the shore line the channel location ran through two small hills, and these have been dug out by steam-shovels to a depth of 41 feet below sea level.

The Pacific entrance or sea-level channel is subject to a maximum tidal oscillation of 20 feet, and therefore the depth has been made 45 feet below mean tide. At the lowest stage of the tide this section of the canal will be 35 feet deep. The channel begins in Panama Bay about four miles from the shore line, and, excepting a mile at the outer end, follows the line of the French canal to Miraflores Locks, a distance of 7 miles, utilizing the French excavation almost the entire distance. The excavation in this section is accomplished by two elevator-dredges of the Belgian type and two Scotch-type elevator-dredges left on the Isthmus by the French, a modern Scotch elevator-dredge built at Renfrew in 1911, and a subaqueous rock breaker of the Lobnitz-ram type. A breakwater extending from the mainland to an island in the bay, parallel with the canal, protects the channel in the bay from cross currents.

The Locks. There are three flights of twin locks on each side of the Isthmus, to accomplish the lift from sea level to the lake level, and vice versa. Thus ships can be locked both up and down at one time, and a stoppage of traffic on account of an accident in one series of locks is anticipated by having a duplicate series. Each lock is a concrete chamber that can be closed at either end by steel gates, so that a ship can be raised or lowered in it simply by admitting or withdrawing water. Each chamber will admit a ship 1,000 feet long and 110 feet wide with a draft of 40 feet. This draft is provided for by a depth of fresh water over the gate sills of 417 feet. This is also the greatest depth at which a vessel can enter New York harbor, and thus there are two factors that will be potent in making it the maximum draft of future ships. The largest ship now projected can easily use the locks of the Panama Canal. Most of the vessels in the isthmian trade or that are likely to be in it for many years to come, in fact 95 per cent of the ocean vessels in the world, are less than 600 feet long; and in order to save water and time in making lockages each lock is divided by intermediate gates into two chambers 400 and 600 feet long, respectively.

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Showing one chamber and method of filling chambers by side and lateral culverts. (A) Operating gallery. (B) Wire Conduits. (C) Drainage culvert. (D and G) Supply culverts. (E and H) Latera' culverts (F) Outlet of Lateral culverts. A cross section of the locks is shown herewith. The main features are the large culverts in the side and center walls through which water is conveyed from the lake level to any part of the locks. From the large culverts it is allowed to flow into or out of the chambers by culverts which open through wells in the floor. The flow into and out of the locks is regulated by valves at the beginning of each culvert. The gates are of the miter type, built up of steel trusses covered with steel plate, forming a series of water-tight bulkheads. Each leaf is 65 feet long, 7 feet thick, and they vary in height fron 47 feet to 82 feet, according to the position in the locks. The gates are set in two pairs, one pair being guard gates for use in case the other gates become damaged or can not be operated, because of repairs to machinery, or from other causes. The arrangement of the gates in the locks is shown by the drawing herewith. In all there are 41 gates

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POSITION OF MITERING LOCK GATES. of two leaves each. They are opened and closed by a steel rod attached to the top of each leaf and to the rim of a large wheel mounted on the lock wall. By rotating the wheel through an arc of 190 degrees the gate is opened or closed, just as one would reach out his arm and open or close a door. (See pages 284 and 285.)

At both entrances to each flight of locks a fender chain is stretched across the channel to prevent ramming of the

gates i' 'case a ship should become unmanageable and enter the locks under its own steam. These chains are lowered to allow a ship in tow of the electric locomotives to pass over them into the locks. In case all the precautions to prevent accident to the gates fail, of if for any reason it is desirable to let the water out of the locks for repairs to the gates, an emergency dam of steel has been placed above each flight of locks, which can be swung across the channel, as a swing bridge is thrown over a waterway, to keep all water from the lake out of the locks. Caissons are also provided.

The gates, fender chain-pumps, emergency dams, towing locomotives, culvert valves, and all accessory machinery will

be operated by electricity generated by waterOperation power at the spillway of Gatun dam, and all of Locks. but the towing locomotives and emergency Material. dams will be controlled from a central sta

tion on the center wall from which all parts of the locks will be visible. The locks are constructed of concrete, of which it is estimated about 4,500,000 cubic yards will be used. The proportions are one of cement, three of sand, and six of rock, and about one barrel of cement is used to each cubic yard. The thickness of the floor depends on the underlying material; in one part of Gatun Locks the floor is 23 feet thick and in another part only 3 feet. The walls are of uniform size; the side walls 50 feet wide at the floor of the locks and graduating to 8 feet at the top, and the center walls 60 feet wide at the floor with an operating tunnel for machinery and power cables at the top.

The locks at Gatun are built through the hill that forms the east abutment of the dam, and are on rock foundation.

The emplacement required six million cubic Gatun Locks. yards of excavation. They are six in number,

three steps of twin locks; each step representing a lift of 28 feet, a total lift of 85 feet. Rock was quarried and crushed at Porto Bello, and sand dug at Nombre de Dios, both historic ports a few miles east of Colon on the Caribbean. These materials were towed in barges to Gatun where they were assembled, and mixed with cement in a concrete plant of eight 2-cubic-yard mixers, that can turn out 400 cubic yards of concrete in an hour. The materials were unloaded at the docks on the French canal, by one set of aerial cableways, and the concrete placed by another,

MR 229286

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