REPORT OF THE CHIEF ENGINEER, ON PLANS FOR CROSSING HARLEM RIVER. New York, June 1st, 1839. To the Honorable the Water Commissioners of the City of New York : GENTLEMEN : The resolution of your Board, requiring the undersigned to prepare plans and estimates for crossing Harlem River, by a bridge, the arches of which shall be

164 MEMOIR OF THE

elevated 100 feet above common high water mark, and also for a tunnel under the channel of the river, has been under consideration.

The law passed at the recent session of the Legislature provides, in relation to a tunnel under Harlem river, that the top of the tunnel shall not be above the natural bed of the river, and that it shall extend across the channel of the same. This will require the abutments to be placed about 300 feet apart, and the top of the masonry of the tunnel about 18 feet below the high water level of the river. In relation to the bridge, the law feet at the under side of the crown, prescribes that the arches in the channel shall be 100 above common high water mark of the river, and not less than 80 feet span conforming in these respects, we are at liberty to make the plans, in all others, without restriction from the law. In the report of the undersigned, made to your Board on the 12th December, 1837, a plan for abridge of sufficient height and stability to support the regular inclination of the aqueduct grade was presented. This plan provided for an aqueduct of masonry, to be rendered more impervious by a cast iron lining; but as it was supposed the Commissioners had power, and no objection having previously been made, on the ground of interference with the the navigation, a structure, conforming nearly to the shape of the valley, and rising to a moderate elevation above the surface of the river, on which iron pipes were to be laid and secured, was recommended, as best adapted for economy, permanence, and more ready execution, to carry the aqueduct across this heavy depression from the grade line.