Illustrations of the Croton Aqueduct

by F. B. Tower

[Plate XI]. is a view taken from a point below the dam and shows the relative positions of the dam and the gate chamber at the head of the Aqueduct.

The original channel of the River where the dam is built, was about 120 feet wide; the average depth of water at this place was about 4 feet; and the greatest depth 10 feet.

The left bank of the river arose abruptly with rock, the channel was gravelly, and on the right bank a sandy table land about 3 feet above the ordinary surface of water extended about 80 feet; then a sandy hill arose on a slope of about forty-five degrees.

In making the plan for a dam at this place it was determined to fill the main channel and the table land on the right bank with an embankment of earth; and on the left bank where rock was found, to build a body of masonry against the slope to the requisite height for the surface of the Reservoir and connect it with the embankment in the channel; this masonry formed the overfall for the water, and the rock in the side of the hill adjacent to it was excavated down to the level of the overfall, thereby extending it into the hill, making the space for the water to pass over partly of masonry and partly of rock. The embankment extended with a slope on the upstream side giving it a broad base, and the lower or downstream side was faced with a heavy wall of stone. There was a timber pier constructed in the embankment extending across the channel and faced with plank on the upstream side. The overfall was made of such length as was thought sufficient to pass all the water of the river during its highest stages, and with the view of adapting it to such purpose, examinations were made to find the highest marks of floods on the banks of the river; and those who were engaged in determining these marks were guided also by the observations of the inhabitants of the vicinity who had long known the river in its various stages. High freshets were witnessed during the construction of the work, for in the course of two years that the work was going up, all the various changes and freshets of rainy seasons were experienced, and those in charge of it did not neglect to note the quantity of water flowing on such occasions.

XI

F. B. Tower.

Gimbrede. sc.

VIEW BELOW THE CROTON DAM.

With such opportunities to become acquainted with the changes of the stream they could not fail to know the quantity of water flowing at periods of the highest freshets, and knowing it, to adapt an overfall of sufficient capacity for its discharge. For this purpose it was thought ample provision was made; yet at the time when the work was nearly completed such a flood occurred as could not have been anticipated from previous knowledge of the River; the water filling the entire passage at the overfall, flowed over the top of the embankment where it was not supposed it could ever reach. The lower slope of this embankment was covered with a wall not calculated to resist the action of the water and it gave way; the water broke through the embankment and rushed along the valley with most disastrous consequences. The breach occurred at an early hour in the morning; and many persons were suddenly aroused from their sleep to escape before the approaching waters. Dwelling-houses and mills were carried away and three lives were lost. Two of those who were drowned had taken refuge in the tops of trees, but these being swept away they were drowned; while others who were not able to reach the main land, but had also taken refuge in trees, were saved. The change wrought by the flood, in the appearance of the country, was truly wonderful and the destruction was complete. Night had closed over that valley where all was happiness and quiet, but day opened upon a scene of desolation. The fertile fields were torn up and covered with masses of stone and gravel, and the flood left marks of its fury far up on the hill sides.