Page:Vol 6 History of Mexico by H H Bancroft.djvu/687

Rh It is proposed to construct a dam on the Corte of suitable strength, 122 feet in length at the lip, and 86 in height.

At this place there is a strong depression or pass in the ridge separating the Corte and Blanco rivers. Taking into account the fall or head to be given to the feeder, the horizontal distance between the Corte and Blanco is 1,750 feet, and the height of the pass above the feeder will be 257 feet. In order to turn the water of the Corte into the feeder, on the Blanco Valley, it will be necessary to excavate less than 400,000 cubic yards upon the ridge which separates the Corte and Blanco valleys. Ihis excavation will just supply the material for the Corte dam, the dam at the Blanco, and the inlet chambers, and the revetement wall of the feeder at the Blanco dam.

A dam 16 feet high must be erected on the Blanco. The river-bed is here 130 feet wide, though the river itself is hardly 20 feet across. The dam, however, will have to be built 140 feet long. Eighty feet of this length will be reserved for the Blanco, and whatever surplus waters may fail to pass through the gates and weirs of the Corte in time of floods.

The balance of the length of Blanco dam will be used for the feeder.

This dam will be pierced by the feeder-chamber, provided with regulating flow-gates, and the waters of the feeder will thus run across the left end of the dam, and between the left bank of the Blanco and a wall buttressing the dam and dividing the waters of the feeder and the Blanco River.

This buttressing and dividing wall will not be more than 300 feet in length, and from this point forward the feeder will run through a side cutting, and entirely above the reach of the heaviest floods. A few hundred feet below the dam a series of falls occur, which make it impossible for extraordinary floods to reach the feeder.

The waters of the Blanco, Maxiponac, Capepac, Coyolapa, Escolapa, Pita, Chichihua, Pericon, Otate (and if necessary the Coquipac) rivers can be utilized to feed the Pacific side-levels, furnishing jointly about 495 cubic feet of water per second. The Corte River will supply any deficit that may occur at the summit for the Pacific side and the upper reaches of the Atlantic side. Water can never be wanting for the summit, because only the Pacific plains will draw heavily from it; while on the Atlantic side not less than 30,000 cubic feet flow into the Coatzacoalcos, between the Almoloya and Uspanapa rivers. This amount is delivered by the Almoloya, Malatengo, Sarabia, Jumuapa, Jaltepec, Chalchijalpa, Naranjo, Coachapa, and Uspanapa rivers, and many other small streams. All the rivers are distributed along the shores of the Coatzacoalcos, at very suitable distances from each other.

The general estimates for water-supply made in the sequel call for 1,618 cubic feet per second, as the amount required to work the whole canal, under the exacting supposition that it is to be fed exclusively from the summit.

The available summit streams were gauged at the height of a remarkably dry season, and found to yield jointly 2,113 cubic feet; so that, strictly speaking, 495 cubic feet per second will have to be disposed of by means of waste-weirs from the very summit, in the driest season, and supposing an extravagant expenditure of water.

Since a large portion of the water brought to the summit is to be used on the Pacific side-slope, this fact might lead to the supposition that the