Bridge at Sing Sing (plan and elevation), c. 1837-39, watercolor and ink on paper Courtesy Jervis Public Library, Rome, NY, drawing #317. Photo: G. R. Farley figure 28. below left: Elevation of a Higli Bridge for Crossing Hariaem [sic] River, c.1839-40. watercolor and ink on paper Courtesy Jervis Public Library, Rome, NY, drawing #249. Photo: G. R. Farley figure 29. above: Pian of Effluent Pipes in East Side of Receiving Reservoir at Yorl< Hill, c.1841, watercolor and ink on paper Courtesy Jervis Public Library, Rome. NY. drawing #307. Photo: G. R. Farley Kemp Inverted siphons As indicated, it is possible to carry an aqueduct below the hydraulic grade line, which is the free surface of the water, diverting it Into pipes which can descend into valleys and rise on the other side. At the lowest point, the water is under maximum pressure which, in effect, forces it up the other side of the Inverted siphon and back Into the open channel of the Aqueduct. In order to avoid major embankments or the use of viaduct bridges it was decided to cross Manhattan Valley with an inverted siphon containing a maximum center depth of 102 feet. Cast iron pipes, each 3 feet in diameter, were originally built and provision was made for two more if the water supplied to New York City had to be augmented in the future. In order to increase the flow through this inverted siphon, the eleva- tion from the entrance to the exit was dropped 3 feet. This is 1 foot more than the decrease in elevation at the High Bridge. In order to avoid the use of an inverted siphon to cross Clenden- ning Valley, a large earth embankment was constructed between 95th and 102nd Streets, approximately 1,900 feet in length with a depression at the center of approximately 50 feet. In order to pro- vide access for streets, three archways or culverts were provided underneath the large embankments. The main archway has a span of 30 feet, whereas the two sidewalks had a reduced span of IOV2 feet. Cast Iron plates were installed over each of the openings for the streets to preclude the entry of water Into the masonry work. From Clendenning Valley, the water was carried in a masonry channel to 85th Street and 7th Avenue, where it entered the first of two reservoirs. The Receiving Reservoir was constructed with a sur- face area of just over 35 acres. It was 1,826 feet long and 836 feet wide. It was divided into two basins so that any settling particles could be cleaned out of one of the basins without closing down the Aqueduct. The north division was designed for a depth of 20 feet, whereas the southern one was increased to a depth of 30 feet. As built, the Reservoir had a capacity of 150 million imperial gallons. From the Receiving Reservoir, the Aqueduct was carried in a series of iron pipes that conveyed water to the Distribution Reservoir located on Mun'ay Hill, now the site of the New York Public Library (figure 29). The Murray Hill Distribution Reservoir reflected the move in architecture during the late 1830s and into the 1840s to identify monumental engineering works with Egyptian revival details (fig- ure 18). Such works were in contrast to Gothic revival structures identified with churches and educational institutions and Classical revival used for public buildings and such structures as banks. In order to provide a sufficient head for distributing the water, it was necessary to build the walls of the Reservoir an average of just over 45 feet above the grades of the street. This would provide an elevation of 115 feet above mean tide. The Reservoir was two city blocks wide and had a capacity of 20 million imperial gallons. From this Reservoir pipes were earned to all parts of the City for the distrib- ution of water for domestic, commercial, and institutional purposes. By constructing a temporary low-level bridge, it was possible to lay Iron pipes across the Harlem River Valley allowing the Aqueduct to be opened before the completion of the High Bridge. On July 4, 1842, the first water was received at the Murray Hill Reservoir amid great acclamation from the citizens of New York City. The High Bridge was not completed until 1848. Notes 1. Charles King, A Memoir of the Construction, Cost, and Capacity of the Croton Aqueduct (New York, 1843), p.220. 2. See selected bibliography on tlie construction of the Croton Aqueduct, p.57 of this book. 3. John Robison, A System of Mechanical Philosophy (Edinburgh, 1804). 4. John B. Jervis, "Memoir presented October 18, 1876,' Transactions of the American Society of Civil Engineers, voi.6, p.55. 5. John B. Jervis, Description of the Croton Aqueduct from the Dam to the Distributing Reservoir (New York, 1842),