Multiple Truths

The next picture from Mr. Tower’s 1843 book on the Croton water system is interesting to me because the subject – the High Bridge over the Harlem River – is the most visible part of the old system and in some ways the least understood.

The Croton River is a tributary of the Hudson, draining an area east of the larger river and some 40 miles north of Manhattan. But Manhattan is an island, so an aqueduct from Croton had to somehow cross the Harlem River, the body of water that separates the Bronx, the southernmost piece of mainland on the east bank of the Hudson, from Manhattan. That’s annoying enough, but the Harlem River isn’t actually a river: it’s a tidal strait connecting the Hudson estuary to the East River. And – stop me if this sounds repetitious – the East River isn’t a river, but rather a tidal straight connecting the Long Island Sound with Upper New York Bay. The natural system of flows is incredibly complex, with fresh water coming down the Hudson and mixing with saltwater from the bay, while the flows in the two straits change direction with each change of tide. The bridge for the aqueduct would have to be a substantial structure.

Almost all of the road bridges over the Harlem are moveable – most are now center-pivot swing bridges – but an aqueduct can’t readily cross a moveable bridge. So the options available in the 1840s were a low bridge that would effectively end navigation on the Harlem or a high bridge. The water commission decided to choose the more difficult option, building a high bridge, to avoid the political fight (and probable loss) over a low bridge. But Mr. Tower’s pretty picture is hiding a secret: the Croton system may have started operations in 1842, but the high bridge wasn’t complete until 1848. A temporary crossing using cast-iron pipe as an inverted siphon was used until the bridge was complete; it’s not clear to me why this option was not used as a permanent crossing.

In the 1920s, about twenty years before the bridge was taken out of service as an aqueduct – replaced by a tunnel far underground – the river-crossing portion was demolished and replaced by a steel arch. The Army Corps of Engineers had stated that the piers for the river arches were a navigation hazard, but that’s an odd position to take for an 80-year-old structure. There are various statements from that time that the Corps was worried about the possibility of aerial bombing blocking the Harlem River with rubble, although I have to say that if an enemy were able to bomb the High Bridge to rubble, New York City would have more serious problems than navigation on the Harlem.

So the picture above is a rendering of an incomplete structure. Here’s a design drawing by John Jervis, the engineer in charge:

Here’s a photograph from 1862, at a time when the original cast-iron pipes were being supplemented by a much larger pipe:

And here’s a reasonably modern view, showing the replacement arch span, highways on both sides of the river, and the Harlem River Railroad in the foreground (on The Bronx side). We’re looking clear across Manhattan to the Hudson and New Jersey.

So, the bridge was possibly never necessary but is the oldest extant bridge in the city, was greatly altered for no good reason but is a considered to be landmark piece of history, and was shown in Tower’s 1843 book as the aqueduct’s Harlem River crossing even though it had barely been begun at that time. And the bridge built solely as an aqueduct is now a pedestrian crossing connecting two small parks.