The New York Rapid-transit Subway

38 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of the subway and substantially at the same level as the original sewer ; secondly, that the longitudinal sewers should be kept as small as possible by diverting the flow at every opportunity into adjacent cross streets leading to the rivers on either side; thirdly, that where the line of the subway deviated from the summit of the drainage-ridge, the drainage from the area thus cut off should be disposed of either by cutting a low-level sewer through the ridge and thus making a new artificial drainage-ridge at the line of the subway, or else by building at some convenient point a new outfall- sewer beneath the subway and taking into it through intercepting sewers the subsidiary drains from the district cutoff. The following Table gives a list of the various sizes of new sewers built, together with the lengths of each :— Feet. Pipe sewers, 6 inches to 4 feet 6 inches .... 45,682'7 Egg-shaped sewers..........................................24,901'9 Circular sewers, 3 feet 9 inches to 15 feet . . , 15,094'0 Irregular shapes............................................2,057'0 Special chambers..............................................238'7 Total ........................87,974'3 From the foregoing it will be seen that in building 14'2 miles of cut-and-cover railway, not less than 17 miles of sewers of various kinds had to be built anew. Portions of the cut-and-cover work, where passing parks and public places, required no sewers on either side, and at other points, for local reasons, sewers were needed on one side only, while the deep-tunnel and elevated sections obviously called for no sewer-reconstruction at all. The building of these sewers did not differ materially in main features from standard sewer-construction elsewhere, except that, especially where sewers had to be curved, it was found advantageous to build them of concrete moulded in place. Where drainage had to be passed across the line of the subway the points of crossing were made as few as possible by building intercepting-sewers on the upper side of the subway and conduct- ing the drainage to a few chosen points. At these points large drop manholes were constructed, leading to chambers connected with iron pipes embedded in concrete and passing beneath the floor of the sub- way. The size of these pipes was regulated not only by the amount of flow, but also by the available height beneath the floor of the subway and the allowable gradient for the sewer. Where this height was not sufficient to permit the flow to be carried in a single pipe, the up-stream chamber was arranged in the shape of a bell-mouth and