Where has Tibbetts Brook Gone?
By Geoffrey Lenat
Tibbets Brook, a babbling brook meandering its way south through Westchester County, and then into Van Cortlandt Park in the Bronx, where it ducks between highways and fairways, and eventually forms Van Cortlandt Lake before suddenly disappearing. Well, it can’t just disappear… the water must go somewhere!
If you are following the brook on a map, tracing its southerly path until it vanishes, you might guess that it should eventually merge with the Harlem River. It did just that until the early 1900’s when the area began to transition from soggy marshland to streets and buildings. The wetlands were filled in and pipes were laid to drain all that pesky water straight to the Harlem River. Tibbetts Brook’s marshiest southern end was diverted into a large brick sewer under Broadway, where it continued its journey to the Harlem River. This is where things got complicated.
(Skip this next paragraph if you’ve already done your homework on combined sewer systems) The problem with most NYC sewers, like many other cities, is that rain water and everything you flush down your toilet (household sewage) flow into the same sewer pipes under the street. The experts call this a combined sewer system. When originally constructed, all that wastewater (rain and toilet) flowed from the sewer pipes directly into our rivers. Eventually, we realized this was a very bad idea, and we built wastewater treatment plantsto clean the sewage before it flowed into our rivers. To get the sewage to these treatment plants, pipes were built to intercept the yucky stuff just before it would pour into the river (interceptors). But, the interceptors are only large enough to handle the sewage you put down your drain at home and at work. When it rains, the rainwater mixes with the household sewage causing the volume of fluid to increase dramatically, and the interceptors can’t handle it. The sewage is then forced to overflow into the river just like it did before the interceptor was built. This is called combined sewer overflow.
That was a long paragraph. (Phew!) The point is that during wet weather, Tibbetts Brook catches rainwater from a large geographic area and funnels ALL OF IT into the combined sewer pipe under Broadway, where it mixes with household sewage and overflows into the Harlem River. This poses a huge problem! We are talking about hundreds of millions of gallons of raw sewage pouring into the Harlem River yearly. Tibbetts Brook accounts for almost a third of the overflow from the Broadway sewer, which is the largest combined sewer outfall in the Bronx by volume.
How can we stop this innocent babbling brook from causing us so much angst?!? All overNYC, the Department of Environmental Protection (DEP) is doing its best to prevent stormwater from entering the sewer system, usually by building a bioswale--a garden that is specially designed to absorb rainwater—just upstream from sewer inlets on streets. Also, new buildings are now required to retain stormwater that falls on them with storage tanks and release it slowly instead of feeding it straight into the combined sewer system. These techniques deal with lots and lots of relatively small sources of stormwater entering the sewer system. Less stormwater entering the sewers means fewer overflows.
However, Tibbetts Brook is a very large single source of stormwater entering the combined sewer system. This is somewhat unusual, and deserves extra special attention. How do we keep all that stormwater from going into the combined sewer system? We certainly can’t absorb Tibbetts Brook with a super-huge bioswale. We could probably come up with some ideas for retaining the stormwater during wet weather, just like new buildings are required to (think huge rain barrel).
The DEP has come up with a plan to address this problem that would 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 a large amount of water during wet weather. This would, in fact, prevent much of the combined sewer overflow I was going on about earlier. The problem is that this plan could be somewhat devastating for natural systems (trees, plants, big critters, little critters, etc.) that depend on the lake in its current form. Also, I have a hunch the scenic qualities of the lake would be negatively impacted by lowering the water level as well.
What if Tibbetts Brook could be diverted before it pours into the combined sewer? This seems like it would be impossible, since we are talking about NYC here. There are streets and buildings covering every last inch of land, so where could we possibly build a bypass or diversion, right? It just so happens that there is a clear path between the spot where Tibbetts Brook pours into the sewer and the Harlem River. The abandoned Putnam Division of the New York Central Railroad (‘Old Put’ for short) passes through Van Cortlandt Park and actually crosses Van Cortlandt Lake twice before continuing south for about a mile and a half and meeting up with the Harlem River.
Old Put has been abandoned for quite some time now (probably because it did not connect directly with Grand Central Station) and much of it has been converted into a multi-use recreational path (rail trail). Yet, the portion of Old Put south of Van Cortland Lake has not been blessed with a rail trail and is still completely abandoned and filled with brambles and litter.
Just to reiterate, there is an empty, unused linear piece of property that stretches between the spot where Tibbetts Brook vanishes into the sewer and the Harlem River. Are you catching my drift? Tibbetts Brook could be reunited with its long lost big brother, the Harlem River, via Old Put. Old Put could host Tibbetts Brook, stopping it from causing all of that combined sewer overflow, AND serve as a recreational corridor for local residents, who currently have little ability to connect with the Harlem Riverfront.
You could call this a daylighting proposition, if you like. Take a look at the recent (and super close-by!) 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. So, they rebuilt the ‘natural’ riverbed for a short stretch in the middle of downtown. The ‘new’ river is now an invaluable amenity for local residents and visitors in downtown Yonkers.
Tibbetts Brook could be ‘rebuilt’ along Old Put. This would be no small feat, but it is certainly possible. City as a Living Laboratory wants to let people know about all of this since it’s easy to miss if you aren’t paying attention. Stay tuned.