« PředchozíPokračovat »
treated by General Abbott, an unquestionable authority, in a separate paper which was embodied in the report. The records of the flow of the Chagres and its tributaries during fifteen years showed 1,250 feet per second in the driest seasons. On a conservative estimate, 2,577 feet per second can be depended on during the entire three months of least rainfall.
“ To determine the number of lockages which this quantity of water will provide for, the following provisions and assumptions have been made: Intermediate gates are to be provided for at Pedro Miguel and Sosa, so as to give a chamber length of 600 feet (the full length of the lock being 900 feet), and it is assumed that the intermediate gates will be used for eighttenths of the lockages. ... It is further assumed that all ships passing in one direction will use one set of locks and all ships passing in the other, another set. (All the locks on the Canal are to be in duplicate.) On this assumption the same quantity of water is used whether a ship passes through a single lock or through two or three in flight. The lift to the normal level at Pedro Miguel is 30 feet and at Gatun 28.50 feet per lock. The quantity of water required per lockage at Pedro Miguel, on the as
sumption that intermediate gates will be used eight-tenths of the time, is 22.13 cubic feet per second, and the quantity per lockage at Gatun 29.77 cubic feet per second, making a total of 51.90 feet per second. The net available quantity of water is, as already stated, 1,350 cubic feet per second, and will therefore provide for 26 lockages per day at each lock in the driest season.'
It is expected and hoped that the traffic will, at no great distance of time, demand a greater number of lockages than the maximum provided for. The present Engineer in Chief is of the opinion that this will come about so soon as to justify the inclusion of an extension of the water supply in the operations now in progress, more especially as a great saving in cost would be effected thereby. He favors the Alhajuela dam and reservoir, which was proposed by the Comité Technique, and which will supply enough water for about thirty additional lockages.
The surface of the Canal, at 85 feet elevation, is the summit level, which is maintained beyond it through the Culebra Cut, a total distance of about 32 miles. The plan of the Board provided for a triple flight of locks in duplicate at
Gatun, by means of which vessels would rise from the channel at sea level to the lake. These locks would permit of two ships passing through them at the same time, and would have the additional advantage that, in case of one set being put into temporary disuse, traffic could be continued through the other. The dimensions of the locks throughout the Canal were to be 900 feet clear length, 95 feet usable width, and 40 feet depth over the miter sill.
Of the total length of the land channel, about 41 miles, more than half lies within the lake, where a broad and deep way is available. The greater part of the Canal course is along straight lines. There are no sharp curves and where changes of direction occur, the outer lines of converging courses are carried to an intersection and the point of the inner angle dredged off, so that a curve of 8,000 or more feet radius can be laid down wholly within the channel. The channel will be nowhere less than 300 feet at the approach to a curve, nor less than 600 feet within it.
The Board's dimensions gave a channel in the Culebra Cut as narrow as 200 feet in places. On the farther side of the Cut the greatest changes that have been made from the plan of