THE NASHUA RESERVOIR.
AKDALE,质量。,几乎是在纳舒厄reservoir to be built for the metropolitan system, and Clinton is at its foot. The reservoir will be eight miles long and at places two miles across. Its area is six and one half square miles and it is thirty-six miles round it. Nature has helped the engineer in the proposed work. Ages ago this territory was a lake, and now all that has to be done to transform it into the largest storage reservoir in the world is to build about two miles of dykes and a 1,250 dam. After clearing away villages, schools, churches, factories, and the like, and removing all the trees, the soil will be scraped to a uniform depth of eleven inches, and about 12,000 feet of wall will be built—thus affording room for the storage of 63,000,000,000 gallons of water. It will take one year and a half to fill this reservoir, with the Nashua river flowing into it all the time. The space thus occupied is one-third larger than Middlesex Falls, and by means of this reservoir Boston and its suburbs will be supplied with good water for forty years, after which other basins will be drawn upon, one of which is smaller and the other six times larger than the Nashua.
The dam will overhang Clinton, from which it will be dis tant only a few hundred feet It will be located across a narrow gorge about 3,000 feet from the dam of the Lancaster mills at Clinton below—which will be supplied by the Metropolitan board with 2,000,000 gallons daily from the Nashua watershed, whose capacity is 100,coo,000 gallons a day—and along the banks of the reservoir the State has planned to provide sewerage. This point was selected and a masonry dam determined upon because of the favorable topography and the fact that here the solid rock nearly approaches the surface of the ground. Extensive borings have been made to determine accurately the form and character of the rock formation; pipes having been driven every twenty feet up and down stream and every ten feet across the deeper portions of the valley—the maximum depth of any hole was 280 feet The results of the borings have demonstrated that the dam can be founded upon solid rock for the entire distance.
As has been already said, the length of the dam at water level will be 1,250 feet ; maximum height of water line above surface of ground, 129 feet; above surface of rock, 184 feet. The water level is 395 feet above low tide at Charlestown Navy yard. The thickness of the dam at water level is nineteen feet.and 145 feet below this level it is to be 110 1-2 feet thick. Four lines of forty-eight-inch pipe will connect the reservoir with the down, stream side of the dam for the joint purpose of supplying water to the aqueduct leading to the Sudbury basins and of conveying the waste water to the river below.
两英里的隧道,削减fifty-five feet below the surface, through solid rock and black schist, connects with a masonry aqueduct, whence the water flows through an open channel to Basin 5 in Southboro. with its capacity of seven and one-half billions of gallons. The tunnel is ten and one-half feet high by eleven and one-half feet wide, and is built in sections of 2,200 feet; and the greatest variation of any of the sections upon their meeting is said to have been one and one-quarter inches. The drilling is all done by compressed air, and mules are used for the cars, as in mines. From Basin 5 the water passes to Basin 3, in use, thence to Basin i.then to Farm pond, Framingham, and, by gravity, through the present Sudbury aqueduct to Chestnut Hill reservoir, where it is joined by the Cochituate system. Then in two forty-eight inch pipes it is carried to Longwood. At that point the line branches through Cottage Farm, crosses the Charles river at Magazine street, and then runs on through Central square, Union square, Walnut street, Somerville, across the Mystic river to Spot pond, where it enters on the north near the Melrose pumping station. Somerville taps this line for her supply at Webster avenue. Pearl and Walnut streets, Broadway, and probably near Middlesex avenue. The other branch from Longwood runs through Allston, crosses the Charles near Harvard square, and continues through Massachusetts avenue, Beach street. Somerville, Willow avenue. College Hill, Medford square, Forest street, to Spot pond at its southeily extremity. Somerville taps this line at Willow avenue and Elm street, and at Willow avenue and Broadway. When completed this will be one of the largest dams in the world. The new dam of the Croton water works in New York, the only one larger, is more extensive in height and length, while the Furens dam in France is somewhat higher and has less length, and the Tansa dam in Bombay is somewhat lower and has a greater length.
The following is a comparative table of areas and capacity of storage reservoirs. It must be noticed that the Ware river and Swift river reservoirs as set down in the table are only prospective.
The maximum depth of the reservoir is 129 feet, and the average forty-six feet.
