NYC: Knickerbocker Avenue Extension Sewer

     In the 1880s, Bushwick was one of the most dynamic and thriving neighborhoods in the city of Brooklyn, NY. It was known especially for its many beer breweries. At the time, Brooklyn was still a separate city from New York City, and it was the third largest city in the United States. (New York City, composed at the time of just the island of Manhattan, was the largest city in the country; the five boroughs of today’s New York City would not be joined until 1898.)
     Both Brooklyn and New York City were growing incredibly rapidly. In the single decade between 1880 and 1890, New York City’s population would grow by 24% from 1.2 to 1.5 million, and Brooklyn’s population would grow an incredibly 42%, from 567,000 to 806,000. Stimulated by explosive growth in the region and fueled with cheap labor, the 1880s saw the opening of some of the most incredible engineering works of the century, including the Statue of Liberty (installed in 1886), and the Brooklyn Bridge (opened in 1883). On a smaller scale, Brooklyn’s first elevated railway opened in 1885, with its eastern terminus at the very edge of Bushwick.   
     The same year, the magazine Scientific American featured a completely different kind of engineering project on the cover of its December 12th issue: a massive 12-foot diameter sewer that was being built to carry the combined sewage and stormwater from Bushwick to a new outlet on the East River.

     From the point of view of an average Bushwick resident, this tunnel was not particularly interesting. Bushwick already had an extensive combined sewer system, with the largest sewer main, which ran along Knickerbocker Street, a full 11 feet in diameter . But the outfall for the Bushwick sewer system was into Newtown Creek, a slow-moving stream that had been turned into a canal. The new sewer featured in Scientific American, called the Knickerbocker Avenue Extension, was built to carry the flow away from its current outfall in Newtown Creek to the East River, about two miles away. For the population of Bushwick, nothing would change; their sewers would function as normal. But the new tunnel would keep sewage away from Newtown Creek’s many fright docks, even as the flow of sewage from Bushwick increased with the population. As the Scientific American article explained:

The necessity for the work is apparent from the fact that the present outlet sewer for this section of the city, which drains an area of about 2,800 acres, some of which is very low and flooded by every rain, is discharged upon the low lands at the head of Newton Creek, making a nuisance greatly detrimental to public health and damaging to valuable property in the vicinity. Frequent complaints from people living near this outlet and by the Department of Health rendered the construction of a new outlet absolutely necessary.

     But, the article explains, “although there is nothing new either in the sewer itself or the duty it is designed to perform, the method of building one section of about three-quarters of a mile in length is certainly unique and interesting.”
     This “unique and interesting” method was the technique used in digging the sewer as a deep tunnel (instead of as an open cut) in the section closest to the East River, where higher land meant that the tunnel was about 65 to 75 feet beneath the surface. To bore a sewer as a deep tunnel instead of as open cut was extremely unusual, and to do it the engineers used a new system of modular iron plates that were inserted at the head of the tunnel to support the roof and sides as the digging was done. Well behind the head of the tunnel, the plates were removed (to be re-used at the front) and bricklayers installed the bricks, set in cement, which would form the 12-inch thick walls of the circular tunnel. An iron-framed five and one-half foot diameter “pilot hole” preceded the main tunnel slightly. As the Scientific American article explains:

This method of tunneling not only gives an exact idea of the nature of the material in advance of the main work, but also served to firmly hold the sides of the excavation, preventing caving in; and where the route extends through a street lined upon each side with houses, and, as in this case, at an unusual depth below the surface, it has many advantages…

     At the time, this was all fairly unusual and impressive from an engineering point of view. The engineer Brunei had been the first to use cast-iron plates as lining for his landmark tunnel under the Thames as far back as 1843, and a train tunnel under the Hudson had even been started in 1874 using some of the same techniques (though that tunnel would not be finished until 1903), but the vast majority of urban tunnels were still built with a cut-and-cover method. The Knickerbocker Avenue Extension marked perhaps the first time that this sort tunneling technology had been used for a sewer or drain.
     This technique is actually very similar to how tunnel boring machines function today, with the cutting head and shield at the very front, and reinforcing plates installed directly behind the shield, providing not only support to the walls of the tunnel, but also bracing for the TBM to push forward. Of course today the digging is done mechanically rather than by manual labor, concrete is poured behind the plates to reinforce the tunnel instead of hand-laid bricks, and the debris or muck is taken out on a conveyor instead of pushed by hand along tracks in small carts as it was in the Knickerbocker extension, but the essential concept is the same and is quite different from the earlier methods of digging-and-blasting ahead of any reinforcement, with bracing only after the tunnel had progressed forward.
     I’d read about this sewer and its construction some years back, and had spent some time walking its route above-ground, or at least as close as I could figure it out. I never found the outfall but spent only a little time looking for it, knowing that the original outfall might be gone-- during the 20th century new development has sometimes changed or covered up original river outfalls. But recently a friend stumbled on the outlet completely by accident. This is how the outfall was described at the time it was built:

The outer end of the outfall is 18 feet in width and 6 1/2 feet in height, measured from the center of the invert, the curve of which has a radius of 41 feet; the sides are vertical, and on them rest iron I-beams, 12 inches deep, and varying in length from 20 feet at the outer end to 13 feet where the outfall sewer joins the circular one.

     Today the outermost iron I-beams have rusted to threads, and the breakdown of bricks and concrete at the top of the outfall makes it look like little more than a pile of debris by the water’s edge. The East River is actually a tidal estuary, and at high tide the water comes within six inches of the top of the outfall tunnel—or higher if there are waves or bad weather.

     I’d had a healthy fear of rising tidewaters ever since the time a few years ago when I was briefly trapped in a storm drain by the incoming tide, so we planned our trip carefully around low tide. It was clear from scouting it that this was still primarily sanitary sewage flowing the pipe, and so we loaded up with protection: we bought hip waders, rubber gloves that went up to the elbow, and wore respirators to keep out any loose particles in the air (though the respirators were unwieldy enough that I soon took mine off). We met up at a bar on the corner of the street above the route of the sewer, just a couple hundred feet from the outfall. When we finally walked into the outfall, it was an hour before low tide, and the water was ankle-deep. We ducked under the rusted I-beams and fallen brickwork, but we only made it about 50 feet in before coming to the floodgates.
     These one-way gates are common now on large CSOs (Combined Sewer Overflows/Outfalls); during normal dry-weather flow, the new interceptor will take the entire flow (of mostly sanitary sewage) to a treatment plant, and gates prevent the incoming tide from flowing back into the system. But during storm events the system maxes out, and the pipes to the treatment plant can take only a small portion of the water, which eventually pushes the gates open and jets out into the bay. Normally, to open the gates for inspection, a truck will hoist the gates up using a chain that goes to the surface. We had no truck, but I had a pair of ratcheting truck tie-downs (good for up to 10,000 pounds), and we were able to pull the gate open slightly by alternating the two— we’d attach one to the chain, tighten it up to open the gate 2-3 inches, then attach the second and tighten it to take the pressure off the first and move the gate another couple inches.
     When we finally had the gates far enough open to slip through I was delighted. Ahead of us stretched the 12-foot high, perfectly circular tunnel lined with hard, dark red bricks. Just in front of us, a catchbasin about six feet long and as wide as the entire tunnel was set into the floor. The fast-moving flow of sewage coming toward it down the tunnel was a little over a foot deep, and it flowed into the catchbasin in a small, powerful waterfall. From the catchbasin, as I knew from sewer maps, it flowed into a 3-foot, 6-inch brick interceptor which led in turn to a 7-foot main interceptor that took it, along with the flow from other old Brooklyn sewers, to nearby treatment plant.
     We carefully climbed around the catchbasin, which was filled with roiling gray water that seemed to be waiting for us to slip even a little on the moist, slick, slimy bricks.

     And, finally, we were in the main tunnel. A 12-foot-high tunnel of hand-laid brick running east-west, 64 feet underneath Williamsburg. A pioneering engineering project from the days when the Brooklyn Bridge and the Statue of Liberty were built. But unlike those monuments, the tunnel we were in had probably averaged less than one visitor a year in the intervening 125 years.      Another few steps and we were almost directly underneath the bar where we’d been drinking just before. We walked about three-quarters of a mile, then turned around and came back. The tide was rising, and we came out through knee-high water around our waders, seeing the lights of Manhattan reflected in the opaque water.

     And really that’s the end of my story. Seems anticlimactic, doesn’t it? But in exploring the urban environment, the fact of us being in the place isn’t the story. Even the process of getting into it isn’t really the story, although it often is close to one. The real story is the hidden thing itself, how it came to be and what it meant to the world. We were just there to see it.