Page:The National Geographic Magazine Vol 16 1905.djvu/520

dam at Bohio; but the trouble with this project is that it entrusts too much to the Bohio dam. If the dam gave way, 10 miles of the waterway would disappear and the canal would be put out of business for years.

The investigations of the American engineers during the past two years have brought to light a number of new and important facts which promise to simplify the two principal engineering problems connected with the canal: (1) The control of the torrential floods from the River Chagresand (2) the Culebra Cut. These results are described by Admiral Chester on pages 462-463. The discovery that it will be necessary to go down 170 feet below sea level instead of 128 feet in order to reach bed rock at Bohio makes the plan of the dam at Bohio almost impracticable. Our American engineers have, however, found a better site for a dam at Gamboa, and it is now proposed to construct the dam to control the Chagres floods at this point. The lake thus created would cover about 10 square miles and would be entirely out of the canal.

The building of the dam at Gamboa will not only furnish complete and effective means of control for the Chagres floods, but it has the further advantage of being entirely accessible by the Panama Railroad for the transportation of men and materials. The plan of the dam will probably require a masonry core, with a great mass of earth and rock fill on either side of it, from the waste excavation of the summit cut.

The conditions attending the construction of this dam are in no way unprecedented. The depth of bed rock below water surface is only about one-third that at Bohio and no greater than has already been reached by the use of heavy timber sheet piling for founding masonry structures in the United States.

The proposed height of this dam from its foundation to its top is far less than found in a number of masonry dams already built, and the making of the earth embankments on the two sides of the masonry core is simply wasting the material from the summit cut. The construction of the Gamboa dam, therefore, involves no formidable obstacles not heretofore successfully encountered in engineering practice.

Experiments made with American steam shovels show that the Culebra Cut can be made in about one-half the time and at about two-thirds the expense formerly estimated. The length of time originally believed necessary to cut Culebra Hill down to sea-level was the reason that the First Isthmian Canal Company recommended a canal with locks. In view of the diminished expense and the great reduction in the estimate of time required for Culebra Cut, general sentiment seems to be that we should construct a sea-level canal and nothing else. But no plan has as yet been definitely adopted.

"I haven't as yet the slightest idea what plan the advisory board will recommend for the Panama Canal, and I am certain that not a member of the board has." These were the parting words of a prominent member of the International Consulting Board of Engineers on the Panama Canal as he stepped on board the steamer which carried the consulting engineers to Panama in September, 1905. The board had been in session for several weeks in Washington. It had listened to the various plans submitted by Messrs Bunau-Varilla, Bates, and others, and had digested the results of the past two years' surveys and investigations on the Isthmus by the Walker and Shonts Commissions. But no vote had been taken, nor is any definite decision to be sought until the board has been carefully over the ground together. Not a single member of the board is new at the Panama problem; every engineer