Where Has Tibbetts Brook Gone?

Tibbets Brook meanders its way south through Westchester County, and then into Van Cortlandt Park in the Bronx, where it ducks between highways, and eventually forms Van Cortlandt Lake before suddenly disappearing. Well, not disappearing exactly, the water does go somewhere, but where? If you follow the brook on a map, you'll notice its southerly path suddenly vanishes. You might guess that it should eventually merge with the Harlem River, and historically it did just that, up until the early 1900's when the area began to transition from a soggy marshland to streets and buildings.  The wetlands were filled in and pipes were installed to drain all the pesky water straight to the Harlem River.  

 

However, this posed a problem because like most cities, NYC sewers use a combined sewer system where the rainwater and household sewage flows into the same sewer pipes under the street.  When originally constructed, the wastewater from the combined sewer system flowed from the sewers directly into our rivers. Eventually, we realized this was a bad idea and wastewater treatment plants were built to clean sewage before it flowed into the rivers.  The pipes that carry the sewage water to the treatment plants were designed to intercept the yucky stuff before it poured into the rivers (interceptors). But, the interceptors are only large enough to handle household sewage, and not large enough to handle rainwater as well. During wet weather, the rainwater mixes with household sewage and this large volume of water overwhelms the interceptors causing an overflow into our rivers (combined sewer overflow).

Tibbetts Brook catches rainwater from a large geographic area and funnels ALL OF IT into the combined sewer pipe under Broadway.  When it rains, this rainwater mixes with household sewage and causes hundreds of millions of gallons of raw sewage to pour into the Harlem River yearly.  Tibbetts Brook accounts for almost a third of the overflow from the Broadway sewer, making it the largest combined sewer outfall in the Bronx by volume. 

What can we do to stop this? All over NYC, the Department of Environmental Protection (DEP) is working to prevent rainwater from entering the sewage system.  The most common technique to accomplish this is by building a bioswale—a garden that is designed to absorb rainwater—upstream from sewer inlets on streets. Also, new buildings are now required to retain rainwater with storage tanks and then release the water slowly to limit overflow.  These techniques deal with a lot of relatively small sources of rain entering the sewage system, but Tibbetts Brook is a very large single source of rainwater entering the combined sewer system. To address this, the DEP has come up with a plan to turn Van Cortlandt Lake into a giant rain barrel.  The plan involves lowering the level of the lake during dry weather, which would allow room for it to fill up and retain more water in the wet weather. The only issue with this is that it could be somewhat devastating for the natural systems (trees, plants, critters, etc.) that depend on the lake in its current form.

What if Tibbetts Brook could be diverted before it pours into the combined sewer? Although this may seem impossible, there is actually a clear path between the spot where Tibbetts Brook pours into the sewer and the Harlem River found in the abandoned Putnam Division of the New York Central Railroad (‘Old Put’). Old Put passes through Van Cortlandt Park and actually crosses Van Cortlandt Lake twice before continuing south to meet up with the Harlem River.  A portion of Old Put has been converted into a multi-use recreational path (rail trail), however, the portion of Old Put south of Van Cortland Lake is completely abandoned and filled with brambles and litter.

You could call this a daylighting proposition, if you like.  Take a look at the Saw Mill River daylighting project in Yonkers.   Saw Mill River was put in a pipe a hundred or so years ago and then recently the decision was made to bring the river back. They rebuilt the ‘natural’ riverbed for a short stretch in the middle of downtown. The ‘new’ river is now an invaluable amenity for Yonkers’ residents and visitors.

If Tibbetts Brook can be rebuilt along Old Put, this could stop all that combined sewer overflow, AND it could serve as a recreational corridor for local residents. This would be no small feat, but it certainly would be possible.  City as a Living Laboratory wants to let people know about all this since it’s easy to miss. Stay tuned!

Where has Tibbetts Brook Gone? has been abbridged by Jamie Phear for the purposes of this blog. Click here to read the full-length version of this article. 

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Geoffrey LenatComment