Upper Delaware Scenic and Recreational River is the home of the oldest existing wire suspension bridge in the United States - the Delaware Aqueduct, or Roebling Bridge as it is now known. Begun in 1847 as one of four suspension aqueducts on the Delaware and Hudson Canal, it was designed by and built under the supervision of John A. Roebling, future engineer of the Brooklyn Bridge.
Portions of the D & H Canal, including the Delaware Aqueduct, were designated a National Historic Landmark in 1968. The Delaware Aqueduct is also designated a National Civil Engineering Landmark.
"Build the Canal above the River"
The Delaware and Hudson (D & H) Canal and Gravity Railroad was a system of transportation between coal fields of northeastern Pennsylvania and markets on the Hudson River. It operated from 1828 until 1898, with enlargements after the 1840s. The Delaware Aqueduct was one of four suspension aqueducts designed by John Roebling for the D & H Canal.
Two important local industries with conflicting needs brought about construction of Roebling's Delaware and Lackawaxen Aqueducts: canal traffic and timber rafting.
Since the mid-1700s, timber from the valley had been floated down the Delaware to shipyards and industries in Trenton and Philadelphia. The D & H Canal's rope ferry crossing of the Delaware at Lackawaxen had been a major bottleneck in the early- to mid-1800s. In addition, there were numerous collisions with timber rafts headed down the Delaware. To alleviate both problems, the D & H Canal Company approved, in 1847, John Roebling's plan to "build the canal above the river."
Compared to conventional bridges, Roebling's suspension design allowed more room for ice floes and river traffic. An immediate success, the $41,750 Delaware Aqueduct and the $18,650 Lackawaxen Aqueduct (no longer standing) reduced canal travel time by one full day, saving thousands of dollars annually.
The aqueduct operated for fifty years until the closing of the canal in 1898. It was then converted to a private toll bridge and underwent a series of modifications through the years. About 1900, new owner Charles Spruks built a tollhouse abutting the New York side of the structure.
Eventually, the towpaths were sawn off and the wooden trunk walls were dismantled. The protective icebreakers were not maintained and were destroyed by the river over time.
The Delaware Aqueduct continued to function as a vehicular bridge until 1979. In 1980, the National Park Service purchased the aqueduct to be preserved as part of Upper Delaware Scenic and Recreational River.
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.
The cable strands are held in place by wrapping wire, which was replaced in 1985, after almost 140 years of use. Roebling's cast iron "pier saddles" still sit astride the cables as they cross original stone piers.
"Cable saddles" each hold a wrought-iron "suspender rod," a bar with both ends hanging vertically from the saddle. Suspenders support part of the aqueduct/bridge flooring by means of a hanger plate.
The wooden superstructure, made of white pine, was replaced about every 25 years by the D & H Canal Company. The last surviving canal-era timbers were removed in the 1930s. In 1986, this superstructure was reconstructed using Roebling's original plans, drawings, notes, and specifications.
In 1995, the wooden ice breakers, towpaths and aqueduct walls were reconstructed.
Today, you may walk across the former aqueduct, following the path taken by canalers and their mules over a century ago. Where canal boats once slowly floated, modern vehicles now cross the Delaware River effortlessly.
Last updated: February 26, 2015