Yesterday afternoon I was tweeting about this insane plan to fill in the East River and replace it with a giant network of highways and parking garages. Obviously if you were going to go to great expense to build additional Manhattan land, the thing to do with it is build buildings on it. Space in Manhattan is very expensive. If you make more of it, you need to fill it up with more Manhattan-esque tall buildings. The other issue here is that in order to keep the shipping lanes to and from the Long Island Sound viable, this calls for digging a giant new canal across Brooklyn and Queens. An even more impractical idea is to drain the Hudson River and then try to divert the flow of water through the Harlem River.
A more reasonable idea, it seems to me, would be to do the reverse of that and drain the Harlem River. It’s not usable for shipping at this point because of the bridges, and it’s just a small tidal basin so I don’t think you’d actually need to divert any water anywhere. Admittedly, this land would be less valuable than what you’d get from the other projects, but it actually seems workable.
It’s interesting to me that we don’t seem to do these large-scale land creation projects anymore. Look at how much bigger Boston got through landfilling. Not only did that creation of the Back Bay area greatly expand the city, it fundamentally alters the geography of Cambridge, which would be much more isolated from the main city with a giant bay over there instead of a small river.