Proposed Aqueduct for New York.
On the 3d instant the Board of Estimate of New York will give a public hearing on the question of constructing a high-pressure aqueduct through the city. The plan is to construct a tunnel 14 feet in diameter through the solid rock base of Manhattan and The Bronx, crossing the Harlem river at a point near Highbridge, and ending at the East river, somewhere opposite Chatham square. The proposed tunnel will be 33 1/2 miles long. 17 1/2 miles of which will be through solid rock. The original plan adopted was to bring the new Catskill supply from the Hill View reservoir, near Yonkers, through steel conduits. Hill View reservoir has an altitude of 295 feet above sea-level. By the new tunnel, it is said, much of the pressure from this point could be conserved by saving of friction of at least 100 feet in the centre of Manhattan. The minimum depth of the tunnel would he 200 feet and maximum depth 600 feet. An estimate made by Assistant Chief Engineer Merriam, of the board of water supply, puts the cost of driving the tunnel at $50,000,000. Then there are to be about 16 miles more of 72-inch steel pipe lines laid throughout the boroughs of Brooklyn, Queens and Richmond. When the matter was brought before the hoard of estimate at its last meeting the proposition was considered, and the following indorsement made: “The modification appears to be a proper one, and its approval is recommended after the required hearing has been given.” An idea of some of the engineering difficulties that may be encountered are: In the preliminary drilling along the route that is being considered tentatively a fissure has been found in the rock base of the island to escape which a siphon will have to be driven down to a depth of 600 feet. Then, it will be necessary to siphon under the East river. The scheme of driving the main pressure tunnel alone is enough of a proposition in itself. In running the tube 200 feet down it will be necessary to have shafts connecting with the surface every half-mile to supply air and to provide for the removal of the exca rated material. No route has been laid out deli nitely, but it is proposed to carry the Manhattan length of the tunnel down Amsterdam avenue to 110th street and then diagonally under C entral I’ark to Fifty-ninth street ; then under Sixth avenue to its junction with Broadway at Thirtyfourth street, where the route will he driven under Broadway to connect with I-ourth avenue and then run under the Bowery to Chatham Square, whence it is proposed to turn eastward to the river. Of this entire route the city would have to condemn not more than 3,300 feet. On the Brooklyn side the proposed siphon would come out about half way between the Manhattan and Brooklyn bridge terminals. As proposed, the plan is to furnish connection with the pressure at as many points along its course as the water board might specify, this connection necessitating the running of pipe connection to lines nearer the surface. At first it was not intended to bring the main line from the Catskills into Manhattan at all. it being proposed to connect this section of the city with the new system only by the 72 inch steel piping which is to he used in the other boroughs. The tunnel is thus a brand new prop osition. Originally the main line from the Catskills was laid out to cross directly into Queens, running thence into Brooklyn and Richmond on a straight line. If the new-idea is approved, in spite of the. doubt as to its cost. Manhattan and The Bronx will absorb the straight line of the new supply, and Queens, Brooklyn and Richmond will he served by branches.