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LIBRARY

OF THE !IVERSITY

OF CALIFORNIA

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300 feet, to Pedro Miguel. There it will enter a lock and be lowered 30 1-3 feet to a small lake, at an elevation of 54 2-3 feet above sea level, and will steam through this for about 112 miles to Miraflores. There it will enter two locks in series and be lowered to the sea level, passing out into the Pacific through a channel about 81/2 miles in length, with a bottom width of 500 feet. The depth of the approach channel on the Atlantic side, where the tidal oscillation does not exceed 11/2 feet, will be 41 feet at mean tide, and on the Pacific side, where the maximum oscillation is 23 feet, the depth will be 45 feet at mean tide.

The Gatun Dam, which will form Gatun Lake by impounding the waters of the Chagres and other streams, will be nearly 11/2 miles long, measured on its crest, nearly 12 mile wide at its base, about 400 feet wide at the top, and its crest, as planned, will be at an elevation of 115 feet above mean sea level, or 30 feet above the normal level of the Lake. The interior of the Dam will be formed of a natural mixture of sand and clay, dredged by hydraulic process from pits above and below the Dam, and placed between two large masses of rock and miscellaneous material, obtained from steam shovel excavation at various points along the Canal. The top and upstream slope will be thoroughly riprapped.

The Spillway is a concrete lined opening, 1,200 feet long and 300 feet wide, cut through a hill of rock nearly in the centre of the Dam, the bottom of the opening being 10 feet above sea level. During the construction of the Dam, all the water discharged from the Chagres and its tributaries will flow through this opening. When construction has sufficiently advanced to permit the Lake to be formed, the Spillway will be closed with a concrete dam, fitted with gates and machinery for regulating the water level of the Lake.

The water level of Lake Gatun, extending through the Culebra Cut, will be maintained at the south end by an earth dam connecting the locks at Pedro Miguel with the high ground to the westward, about 1,700 feet long, with its crest at an elevation of 105 feet above mean tide.

A small lake between the locks at Pedro Miguel and those at Miraflores will be formed by dams connecting the walls of Miraflores locks with the high ground on either side. The dam to the westward will be earth, about 2,700

[graphic]

LOOKING SOUTH FROM THE EAST WALL, UPPER GATUN LOCK, MARCH 1, 1910.

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