system. Another was the nearly 40-mile-long tunnel needed to carry the Croton water from the Dam to the Distributing Reservoir on Murray Hill, between 5th and 6th Avenues, from 40th Street to 42nd Street (figure 16). Douglass proposed that the tun- nel be constructed of stone with the top arched, the bottom an inverted arch, and the side walls tapering slightly inward toward the bottom. The brick- and stone-lined Interior would be 7 feet 5 inches figure 13. above: Method of Construction on Steep Side Hiils [detail], c.1837-39, watercolor and ink on paper Courtesy Jervis Public Library, drawing #199. Photo: G. R. Farley figure 14, middle: Transverse Sections of Plans for the Croton Aqueduct, submitted by John B. Jervis In report of Dec. 23. 1836. ink and watercolor on paper Courtesy Jervis Public Library, drawing #161. Photo: G. R. Farley figure 15, below: Robert Havell. Jr., View of Croton Dam. engraved by Henry Jordan & Frederick Halpin, frontispiece from Charles King's A Memoir of the Construction, Costs and Capacity of the Croton Aqueduct .... New York. 1843 The Hudson River Museum of Westchester, Gift of John Zukowsky. Photo: B. Sigler wide and 8 feet SVs inches high, at its greatest. Thirty-three venti- lators were built at mile intervals to provide air circulation and tun- nel access. Six waste weirs would allow for the exit of excess water and 114 stone culverts would carry the Aqueduct across the numer- ous small streams along the route. Jervis altered the Douglass plan only in the shape of the tunnel. He redesigned the vertical walls to make the space between them somewhat wider at the low- er end than called for by Douglass. This would make the sidewalls 4 feet high instead of 4.2 feet and save a total of $500,000 along the entire length of the tunnel. It would also allow for a greater dis- charge Of water than the original specifications. In addition to its many culverts, four much larger structures were designed to cross large streams and wide depressions in the land. The plans called for an 88-foot-long bridge across the Sing Sing Kill, an iron pipeline laid atop an earthen embankment across the 4,180-foot-wide Manhattan Valley, a 1,900-foot-long masonry wall across the Clendenning Valley with archways to accommodate the streets planned for upper Manhattan and, of course, the magnificent Harlem River Aqueduct Bridge. Jervis' planning for the figure 16, above: David B. Douglass, Map of the Water Region/Counties of Westchester and Putnam/Exhibiting the various lines of Aqueduct for sup- plying the City of New York with Pure and Wholesome Water, c.1835 Courtesy Jervis Public Library, (not in exhibition). Photo: G. R. Farley figure 17. right: Fayette B. Tower, Croton Aqueduct at Sing Sing Kill, C.1842. ink on paper Courtesy Helen Tower Wilson. Photo: T. Harnik Sing Sing Bridge can serve as an example of how the chief engi- 21 neer drevj on prior knowledge and experience in deciding upon the design and material for the structure (figure 17). In a report to the Water Commissioners dated February 8, 1837, the chief engineer cited both the High Falls Aqueduct on the Delaware and Hudson Canal and the Little Falls Aqueduct on the Erie Canal as examples of masonry watenway structures. Having worked on both canals he was familiar with the aqueducts and their durability. He noted that the 15-year-old Little Falls Aqueduct had suffered considerably from the frost even though it was laid in hydraulic cement. The ten-year-old High Falls structure fared better due to the draining of the canal water at the end of the navigation season. But Jervis considered all masonry aqueducts too prone to leakage to be acceptable for the Croton requirements. For a solu- tion, Jervis turned to the work of English engineers, in particular the Chirk Aqueduct on the Ellesmere Canal and the Slateford Aqueduct on the Edinburgh and Glasgow Union Canal. In both structures. CMij'siJiH jMiVJi-udvj: i-.. £:iiVii as.-sc Larkin cast iron was used for the bottom and in one, for the sides of the water channel. Since the Chirk Aqueduct, for example, was still water-tight after 30 years of use, the design that Jervis recommend- ed was an amalgam of the American and English works, a masonry structure with the waterway lined with cast Iron. In suggesting the design for the Sing Sing Aqueduct Bridge, Jervis revealed early in 1837 the approach he would take in plan- ning the building of the other major structures of the Croton sys- tem. He informed the Water Commissioners that his object was to use a "plain and substantial style of architecture," and to avoid ornamentation except that necessary to the stability and longevity of the work. It is interesting to note that the chief engineer consid- figure 18: James Renwick, Jr., Distributing Reservoir, watercolor in "Letter Book