Illustrations of the Croton Aqueduct

by F. B. Tower

The disadvantages attendant upon an open canal were, that by filtration through the banks there would be a heavy loss of water;—the difficulty of preserving the water from receiving the wash of the country, and preventing injurious matter from being thrown into it and rendering it impure, and the impurities which might be contracted by passing through different earths. Evaporation would also occasion a serious loss of water. The banks would be liable to failure in seasons of long-continued rains, and the city depending upon this for a supply, would be cut off, except there should be sufficient in the reservoirs to furnish a supply during the period of repairs. The canal could never be subjected to a thorough repair, because of the necessity of keeping it in a condition for furnishing water constantly during the whole year, so that all repairs would be done under great disadvantages, and the channel would be yearly growing worse until its failure might become a public calamity. In regard to the open channel having the sides protected by masonry, the objections were found to be such as would apply equally to every species of open channel; namely, that it would be exposed in many situations to receive the wash of the country; that it would be unprotected from the frost, and liable to be interrupted thereby, and lastly, that there would be a loss by evaporation. It was supposed that these objections might be obviated by certain precautions; for example, the wash could be avoided by making sufficient side drains; and the interruption liable to occur from frost and snow, and the evaporation, to a certain extent, could be prevented by closing the channel entirely with a roof over the top. The close channel or culvert, composed essentially of masonry seemed to possess all the requisite advantages for conducting the water in a pure state and keeping it beyond the influence of frost or any interruption which would be liable to occur to an open channel. In point of stability this plan had a decided preference over either of the other plans proposed, and the only objection offered was the cost of the work constructed in this way. To avoid too great expense it was proposed to make use of a mixed construction, using the close channel or culvert in situations where deep excavations occurred and it would be desirable to fill in the earth again to the natural form, also where the line of Aqueduct intersected villages, and using the open channel with slope walls for the residue of the distance.

In regard to iron pipes for conducting the water, it was found that a sufficient number of them to give the same sectional area as would be adopted by either of the other plans would be more expensive, and considering the great distance and the undulating surface over which they would extend, other disadvantages were presented which added to the objections, and the plan was considered inexpedient. Could a line be graded so as to give a regular inclination from the Fountain Reservoir to one at the city, then the expense of laying iron pipes for conducting the proposed quantity of water, would be greater than for constructing a channel-way of masonry; and when laid, the pipes were thought to be less durable. Should the pipes follow the natural undulations of the ground, there would be so much resistance offered to the flow of water that the discharge would be diminished in a very great degree.

The close channel or conduit of masonry was adopted as the plan best calculated to answer all the purposes of conducting the water to the city.

Sources of the Croton River.

The sources of the Croton River are principally in the county of Putnam, at a distance of fifty miles from the city of New-York; they are mostly springs which in that elevated and uneven country have formed many ponds and lakes never-failing in their supply. There are about twenty of these lakes which constitute the sources of the Croton River, and the aggregate of their surface areas is about three thousand eight hundred acres.

From these sources to the mouth of the Croton at the head of Tappan Bay in the Hudson, the distance is about twenty-five miles. The country bordering upon the Croton is generally elevated and uneven, not sustaining a dense population and cleared sufficiently to prevent injury to the water from decayed vegetable matter. The river has a rapid descent and flows over a bed of gravel and masses of broken rock. From these advantages there is good reason to suppose that the water will receive very little impurity from the wash of the country through which it flows, and there is no doubt that the sources furnish that which is peculiarly adapted to all the purposes of a large city.

The water is of such uncommon purity that in earlier days the native Indian gave a name to the river which signified “clear water.”[5]

Flow of Water in the Croton River, Capacity of the Fountain Reservoir, &c.

The medium flow of water in the Croton, where the fountain reservoir is formed, exceeds fifty millions of gallons in twenty-four hours, and the minimum flow, after a long-continued drought, is about twenty-seven millions of gallons in twenty-four hours.

The dam on the Croton River is about 38 feet above the level which was the surface of the natural flow of water at that place, and sets the water back about six miles, forming the Fountain Reservoir which covers an area of about four hundred acres. The country forming the valley of the River was such as to give bold shores to this reservoir generally, and in cases where there was a gentle slope or a level of the ground near the surface of water, excavations were made so that the water should not be of less depth than four and a half feet.