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swamps. A great deal of submarine rock was excavated, partly through the use of a Lobnitz rockbreaker, which shattered the rock by dropping a heavy cylindrical shaft, and partly through the usual process of submarine drilling and blasting. (See plan No. 3.)

It was originally intended to carry the canal into deep water on the easterly side of the group of islands Naos, Culebra and Flamenco, which lie about 3 miles off the Pacific shore. A study of the conditions developed the fact that the strong littoral currents carried silt in a westerly direction, and as the shores of the bay are lined with a very fine mud, this action would cause the dredged channel to fill rapidly. For these reasons it was decided to carry the channel to deep water on the west of the group of islands, and to build a breakwater or dike from the shore at Balboa to Naos Island, about parallel to the canal. The object of the breakwater was not to give protection from seas or storms, for these are unknown on the Pacific side of the Isthmus, but to prevent the movement of silt into the canal, to shut off the swift tidal currents which would carry vessels at right angles to their course and, incidentally, to provide a roadway from the mainland to the fortifications on the islands. An ample amount of material was available from the excavations in the Culebra Cut, which necessarily required disposal somewhere. The breakwater, or dike, was built by means of a trestle of creosoted timber piles, from which railroad cars dumped their material into the water. The trestle was over three miles in length, and as stated in the annual reports of the commission, was driven for a greater part of its length in blue mud, varying from a few feet to 102 feet in depth. The mud particles are exceedingly fine, and the substance feels greasy and slippery, and has a very low coefficient of friction. The mud was not able to carry the weight of the stone dumped from the trestle, and the stone and trestle were continually sinking and shifting laterally. At one locality, the total vertical displacement aggregated 125 feet in a single year. In some cases the lateral displacement of the trestle was as much as 300 feet. The pressure of the stone was most effective when a 20-foot tide was out, and the displacements usually occurred at low water. The rock in settling caused parallel ridges of mud to rise about 80 feet from the center of the track. At one point a record was kept of the amount of material required to bring the stone fill up to the required height of 29 feet above the original bottom, and it was actually ten times as much as computations taking no account of settlement indicated necessary. Such occurrences might have been very serious, but in this case unlimited material was available from the cut, and the total cost of the work was not excessive. In fact, the total cost of the dike up to December 31, 1912, was $300,000 for 1,121,000 cubic yards, or at the rate of about 27 cents per cubic yard, or about $13.00 per lineal foot. Costs are exclusive of the amount that would have been spent to dispose of the materials on the ordinary dumps.

The principal ship repair plant will be on the Pacific end of the canal. There will be a large dry dock, equal in capacity to that of the locks, with an entrance of at least 110 feet clear width and a clear length of 1,000 feet. A smaller dry dock may also be built. The ship repair yard is designed to afford repair facilities for all of the Panama Canal plant, and for visiting ships. It will comprise foundries, machine shops, equipment for shipfitting, woodworking, paint shops, storehouses, and all the other necessary outfit for the great variety of work that it will be called upon to do. Its general character will be similar to that of a large navy yar The plant will be a valuable asset to the United States Navy, especially in time of war. There is at present a small dock and repair plant at the Atlantic end.

Unloading piers are being provided at Balboa in addition to the present facilities, as at Cristobal. It is probable that there will be an anchorage basin near the dock yard, though rock bottom is a deterrent influence.

Two of the largest floating cranes in the world, German built, form a part of the equipment, and these are of the revolving type. They have a lifting capacity of 250 tons at 22 feet reach, or 150 tons at 62 feet reach, and 100 tons at 82 feet, with a hook 100 feet above the surface of the water. Their stability will be retained under any and all conditions of loading, without shifting ballast or counterweight, except that the revolving structure will be counterweighted. The two cranes acting together will be able to lift any one of the enormous leaves of the mitering lock gates.

The coaling plant at the Pacific end will have a total storage capacity of 135,000 tons, of which 75,000 tons will be subaqueous. Arrangements are made for separate storage of coal belonging to different owners. The capacity of the plant for unloading from colliers will be 500 tons per hour, and the total issuing capacity will be 1000 tons per hour. It is proposed to furnish coal by sale to passing vessels. The Cristobal coaling plant will be larger, and will have a total storage capacity of about 240,000 tons, of which 125,000 tons will be subaqueous. The capacity for unloading from colliers will be 1000 tons per hour, and the total issuing capacity will be 2000 tons per hour. While private owners and steamship companies will be permitted to store their own coal in this plant, the government will do all the handling. The government will own and operate a large number of coal and oil lighters at each end of the canal. Oil storage and an oil pipe line across the Isthmus will also be provided.

CONTROL OF WATER DURING CONSTRUCTION OF THE CANAL

One of the serious problems that arose in connection with the actual construction of various parts of the canal has not been mentioned in describing items such as the locks, dams, and Culebra Cut, because it can be better treated as an individual subject. We realize that the canal is built in the valleys of the Chagres and Rio Grande Rivers, and that the route selected is the very lowest one that could be found. Knowing the character of tropical rainstorms and river floods, it needs but a moment's thought to make clear the seriousness of the problem of keeping the storm waters and the floods away from the construction work. Improperly or insufficiently controlled, these waters

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Fig. 18. — Pedro Miguel Locks Control House, showing switchboard for operating valves and gates,

and showing also indicating devices.

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