Mysteries of the Old Croton Trail

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The debate over whether to pave the Putnam Trail has inflamed passions among Van Cortlandt Park regulars. On a recent Saturday, they flocked to hear Urban Park Rangers explain the elaborate system of another trail that crosses the park — “the snake that is the Croton Aqueduct.”

“Imagine the shape of an egg elongated into a tube,” Ranger Grant Wheeler, who planned the tour, explained to a group of about 40 children and adults.

That tube, now buried beneath rocks, dirt and vines in the northeast corner of the park, only measures about seven and a half feet wide by eight and a half feet tall. But using “ancient technology” pioneered by the Romans, the 41-mile aqueduct, which opened in 1842, allowed New York City’s population to boom by a factor of three between 1850 and 1880.

Before the aqueduct, one in 39 city residents died as a result of contaminated water.

“The fecal matter of the horse carriages swirled in the air,” Mr. Wheeler told his audience. “And after that came the cholera epidemic. People with means wanted to get out of the city and live in places like Westchester.”

With the aqueduct came clean water for more residents, though not without complications. As new water flowed into the city, the water table raised and flooding became common. A sewer system was needed, and over the next few years, close to 150 miles of subterranean passages were carved.

Instead of gears, the aqueduct relied on the power of gravity and forced compression. As it descended from Croton Lake, it narrowed ever so slightly as it closed in on the Murray Hill reservoir, located at the site where the New York Public Library now stands. In the mid 1800s reservoirs were above ground, so that gravity could be relied on to distribute the water to thousands of different homes.

To divert and regulate the flow of water, way stations known as weirs were used. Van Cortlandt Park’s Croton Trail is home to the last such structure in the Bronx.

Weirs mimic the vascular tissue of trees. Water flows into a pan at the bottom of the blockhouse-like structure, then takes advantage of capillary action and surface tension to travel up a thin tube to a slightly higher pan. This process could repeat itself dozens of times for an untold interval, Mr. Wheeler said.

Further along the path toward the Putnam Trail, the ranger stopped to guess the age of a cliff face composed of metamorphic rock.

“It’s great you can touch this,” he said. “This is 1842 right here. All you have to do is peel off a thin veneer, and history just drips out.”

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