By Vladimir Brezina
These tropical storms have certainly stirred things up! Hurricane Irene came through ten days ago and deluged the entire region, and a couple of days ago Tropical Storm Lee repeated the performance. This morning, looking out of the window on Manhattan’s Upper East Side, we saw a strange sight in Hell Gate…
Hell Gate is the three-way confluence of the Lower East River (to the right in the photo below), the Upper East River (through Hell Gate proper, under the bridges to the left rear), and the Harlem River (to the left front). In the middle (behind the two tall buildings) is Mill Rock island. (Click on the photos to expand.)
About two hours after the start of the ebb in the East River, a powerful ebb current was bringing blue Long Island Sound water down the East River. But, demarcated from the blue water by a meandering but sharp boundary, the Harlem River water was a light, even slightly reddish, brown.
The complicated boundary between the blue and brown water changed as we watched over the next couple of hours, in a nice visualization of the complex dynamics of the currents in Hell Gate (well known to us as kayakers!).
Interestingly, boat wakes cleaved through the brown water to blue water underneath, revealing a vertical separation as well:
What was the brown stuff?
It could have been runoff sediment. Huge amounts of silt and mud have been coming down the Hudson River (to which the Harlem River connects at its other end) ever since Irene:
The sediment flux from Irene is really massive…unusual, but not unheard of,” said coastal oceanographer David Ralston of the Woods Hole Oceanographic Institution. “One big event like this can move and deposit as much sediment as you might get in several years of regular flow on the Hudson.
(See also here and, for a good example just a little farther afield, here.)
Alternatively, the brown stuff could have been an algal bloom, promoted by the nutrients, both natural and man-made, that have been stirred up from the bottom or brought down by the runoff.
The runoff has brought down with it, too, vast quantities of larger floating debris—tree branches, logs, and all kinds of plastic trash—that have accumulated in embayments around the harbor, and which the skim boats of the Army Corps of Engineers are busy scooping up.
Altogether, New York Harbor has taken quite a few hits this summer. In July, there was the massive sewage release from Manhattan’s North River Wastewater Treatment Plant that closed beaches and disrupted recreational activities and businesses throughout New York City. Soon after, there was another significant sewage spill at Ossining that spread sewage up and down the Hudson River. And now, the lasting mess made by Irene and Lee…
On the bright side, though, the fast ebb current due to Irene’s runoff has contributed to at least one swim record in New York Harbor…
Tugster has posted photos of similar phenomena in the Kill van Kull, as well as farther north up the Hudson River, here.
Vladimir Brezina (RIP) 
Johna Till Johnson
Wind Against Current 
The water conditions have now forced the cancellation of NYC Swim’s Governors Island Swim that was scheduled for this weekend…
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i have similar brown/black water pics i took yesterday near the entrance to the kvk. i’ll post them next week some time. interesting shots you have here.
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The red is appearently Catskill clay in suspension from Irene. See http://cityroom.blogs.nytimes.com/2011/09/07/the-hudson-is-red-but-its-probably-not-a-sign-to-repent/ …the red (fresh water) moving atop the blue (LI sound sea water) makes sense as fresh water is lighter.
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Tom,
Thanks for the link to that article, which I hadn’t seen previously.
I am a little dubious about the surface layer being anywhere close to fresh water, still unmixed this far south. What is possible, however (and this is what you may have been suggesting), is that the water coming down the Harlem River from the Hudson has lower salinity than the East River water, because of all the fresh water mixing into the Hudson. I am pretty sure such a salinity difference between the Hudson and East Rivers exists even in normal times—we can taste it when kayaking! This seems like a perfect question for SeaAndSkyNY to answer…
More generally, I remember going out kayaking the day after Hurricane Floyd (1999) and the water was a light chocolate brown and extremely opaque—I couldn’t see even an inch into it—as well as very high and full of floating broken trees…
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You are right…I should have said ‘relatively fresh Harlem River waters’ vs. saltier and therefore heavier LI Sound waters. Calling Harlem River water fresh is inaccurate in so many ways.
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Stevens (more formally, the Urban Ocean Observatory at the Center for Maritime Systems of the Stevens Institute of Technology :-) ) has has some interesting data, visualizations, and predictions concerning the salinity.
First of all, the salinity in the Hudson River on the West Side of Manhattan has dropped dramatically in the last few days, and the tidal oscillations in salinity have been much attenuated, presumably due to the runoff water now reaching New York City from upstream:
Second, there is indeed a big difference in salinity between the Hudson and East Rivers:
Finally, Stevens’ model simulations show how, as the tidal currents in the Hudson and East Rivers flood and ebb, the Hudson and East Rivers alternately push water with lower and higher salinity, respectively, into the Harlem River. But the salinity changes in the Harlem River are delayed with respect to the tidal currents, and there are interesting differences between the surface and bottom salinities… This needs further study :-)
In short, all of this is consistent with the idea of the Hudson’s muddy brown and relatively fresh water invading the Harlem River and even exiting into the East River as a relatively thin surface layer…
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