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Page:Popular Science Monthly Volume 61.djvu/273

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267
THE PANAMA ROUTE FOR A SHIP CANAL.

of the Chagres, therefore, instead of constituting the obstacle to construction and convenient maintenance of the canal heretofore supposed are deprived of all their prejudicial effects and transformed into beneficial agents for the operation of the waterway.

The highest floods are of short duration, and it can be stated as a general law that the higher the flood the shorter its duration. The great floods which it is necessary to consider in connection with the maintenance and operation of this canal would last but a comparatively few hours only. The great flood flow of 140,000 cu. ft. per second would increase the current in the narrowest part of the canal below Obispo to possibly 5 ft. per second for a few hours only, but that is the only inconvenience which would result from such a flood discharge. That velocity could be reduced by additional excavation.

Inasmuch as this system of control, devised and adopted by the Isthmian Canal Commission, is completely effective in regulating the Chagres floods, the reservoir proposed to be constructed, by the new Panama Canal Company at Alhajuela on the Chagres about twelve miles above Obispo, is not required, and the cost of its construction would be avoided. It could, however, as a project be held in reserve. If the traffic of the canal should increase to such an extent that more water would be needed for feeding the summit level the dam could be built at Alhajuela so as to impound enough additional water to accommodate, with that stored in Lake Bohio, at least five times the 10,000,000 annual traffic already considered. Its existence would at the same time act with substantial effect in controlling the Chagres floods and relieve the Gigante Spillway of a corresponding amount of duty.

The locks on the Panama route are designed to have the same dimensions as those in Nicaragua, as was stated in the lecture on that route. The usable length is 710 ft. and the clear width 81 ft. They would be built chiefly of concrete masonry while the gates would be of steel, and of the mitre type.

The great dam at Bohio raises the water surface in the canal from sea-level in the Atlantic maritime section to an ordinary maximum of 90 ft. above sea-level; in other words, the maximum ordinary total lift would be 90 ft. This total lift is divided into parts of 15 ft. each. There is therefore a flight of two locks at Bohio, indeed there are two flights side by side as the twin arrangement is designed to be used at all lock sites on both routes. The general dimensions and the arrangements of these locks with the requisite culverts and other features are shown in the acompanying plans and sections. They are not essentially different from other great modern ship canal locks. The excavation for the Bohio locks is made in a rocky hill against which the southwesterly end of the proposed Bohio dam rests and they are less than one thousand feet from it.