1848,1987 Roebling D&H Canal Delaware Aqueduct over Delaware River at Lackawaxen, PA

(Historic Bridges; HAER; Satellite, 1,386 photos)

HAER PA,52-LACK,1--58 (CT)
58. Perspective from the west bank from the northwest. - Delaware & Hudson Canal, Delaware Aqueduct, Spanning Delaware River, Lackawaxen, Pike County, PA

"Significance: Probably the oldest suspension bridge in the United States that retains its original elements and the earliest extant example of Roebling's engineering genius., The Secretary of the U.S. Department of the Interior has designated the Delaware and Hudson Canal a National Historic Landmark, and an NHL bronze plaque has been placed on the aqueduct. New York State has also recognized the structure with a roadside historical marker." Before the aqueduct was built, a dam across the river created a slack pool, and locks on both riverbanks were used to get barges down to the river level. [HAER_data, this reference includes a short history of the D&H Canal.]

Street View, Aug 2019

Bob Dover posted

The Delaware Aqueduct crossing the Delaware River from Minisink, New York to Lackawaxen, Pennsylvania, is a famous tourist bridge for a few reasons. Dating from 1848, it is the oldest suspension bridge in the United States, which should be reason enough. It is also one of three remaining bridges designed by John Roebling, and was one of the first-ever uses of wire rope suspension technology.

The aqueduct was one of four that Roebling built as part of the Delaware and Hudson (D&H) Canal system. The D&H Canal opened in 1828, and had four locations where boats on the canal needed to cross the river itself. As part of an expansion of the canal in 1848, Roebling constructed these four aqueducts, but not for pedestrian or horse traffic. Instead, each aqueduct was a water-tight trough, large enough to carry boats and suspended high enough above the river so that other boats could still pass underneath.

A more detailed description of the Delaware Aqueduct is included in Chapter 3 of my book, Bridgespotting: A Guide to Bridges that Connect People, Places, and Times. I have also added several photos of it to the Delaware River gallery on www.bridgespotting.com.

Robert Vogel Photo via HistoricBridges
The most recent rehabilitation, 1987, makes it hard to see the suspension cables because it "restored the original timber design that once held the waters of the canal, although it retains a design that accommodates vehicular traffic....The Delaware and Hudson Canal is the oldest transportation company continuously operating in America." The canal was made obsolete by the Delaware & Hudson Railroad.
HistoricBridges gives this bridge its highest rating of 10 out of 10 for both National and Local significance.

UncoveringNewYork
The aqueduct spans 535' (163m).This is the only one of Roeblings four D&H aqueducts that is still standing.

pabook, Derek Ramsey
The clearance under the trough, which holds 2000 tons of water, is 30' (9m). The cables were made from wrought iron, not steel. "These iron cables are what set Roebling’s design apart. During the time when the Delaware Aqueduct was built, suspension bridges, or bridges in which the deck (load-bearing surface) is suspended below support cables, commonly used open link chains. Roebling’s use of wire rope, an attribute now inseparable from major suspension bridges, revolutionized the bridge industry and has helped the Delaware Aqueduct stand the test of time, making it the oldest suspension bridge in the United States....Wire rope suspension bridges, which supported their loads via massive iron cables, offered an efficient, cost-effective solution capable of supporting heavier loads over longer spans. Roebling’s design in specific presented three major advantages over the truss bridges of his competitors: it allowed the river to be crossed in fewer spans, it increased the clearance between the bridge and the water’s surface, and it was much cheaper."
It needed just three piers. (The spans were one of 142' (43.3m) and three of 131' (40m).) A contemporary truss bridge would require four or five piers. Fewer piers not only reduced the cost, but it also reduced the impedance to ice flows and logging rafts. 
["Since the mid-1700s, timber from the valley had been floated down the Delaware to shipyards and industries in Trenton and Philadelphia." [nps_roebling]]
The National Park Service bought the structure in 1980 and rebuilt it to the original specifications. And a concrete roadbed was used to emulate the weight of the water in the trough. A lot of static weight was needed to reduce the impact of moving live loads. The reduced impact restored the stability of the cable system.

nps-roebling
"Almost all of the Delaware Aqueduct's existing ironwork — cables, saddles, and suspenders — are the same materials installed when the structure was built. The two suspension cables are made of wrought iron strands, spun on site under the direction of John Roebling in 1847. Each 8 1/2-inch diameter suspension cable carries 2,150 wires bunched into seven strands. Laboratory tests in 1983 concluded that the cable was still "viable;" some of the wires even exceeded Roebling's original specifications."

nps_canal
"Stock prices fluctuated during the early years, but by 1848 the D & H Canal was likely the nation's largest private corporation....In the late 1840s and 1850s, the canal's trunk was deepened to 5, then 6, feet. Its locks were enlarged to 90' x 15', increasing its capacity from 200,000 tons to one million tons of coal annually. Forty- ton capacity boats were gradually replaced by boats of up to 140 tons, which could go directly from the canal to markets up and down the Hudson."