3 ms·

It's a 60 mile long tunnel and in order for water to flow through it, you need either pumps or a downhill gradient. I'd guess the reason for the 800 ft is beca

by cogman10 10mo ago

It's a 60 mile long tunnel and in order for water to flow through it, you need either pumps or a downhill gradient. I'd guess the reason for the 800 ft is because the reservoir it'll draw from is near sea level.

nuccy 10mo ago
Rivers (e.g. Mississipi) work with much smaller gradient of just 0.01% [1], while with your assumption it would be 0.25%, so 25x. Maybe instead it needs to pass under the rivers [2: cross-section] surrounding New-York, which may be much deeper, especially when it comes closer to the bay passing Queens and Brooklyn [2: map] 1. https://en.wikipedia.org/wiki/Mississippi_River https://en.wikipedia.org/wiki/Mississippi_River 2. https://gordonsurbanmorphology.wordpress.com/2014/10/26/waterworks-manhattan/ https://gordonsurbanmorphology.wordpress.com/2014/10/26/wate...
- woodruffw 10mo ago
  This piqued my interest, so I checked: Tunnel #3 passes under the Harlem River and then the East River, but the Harlem River is less than 30 feet deep for the most part and the East River is around 40 feet deep at the most. (The Army Corps of Engineers has great detailed depth surveys for most of NY's waterways[1].) Edit: There's also a higher-resolution render of the tunnel layout here[2]. [1]: https://www.nan.usace.army.mil/Missions/Navigation/Controlling-Depth-Reports/ https://www.nan.usace.army.mil/Missions/Navigation/Controlli... [2]: https://extapps.dec.ny.gov/docs/water_pdf/nycsystem.pdf https://extapps.dec.ny.gov/docs/water_pdf/nycsystem.pdf
woodruffw 10mo ago
> I'd guess the reason for the 800 ft is because the reservoir it'll draw from is near sea level. I believe Tunnel #3 connects to the Catskill Aqueduct[1], which draws from the Schoharie and Ashokan reservoirs. Both are at least a few hundred feet above sea level (the Ashokan is about 600 feet above, since it was formed by flooding a valley in the Catskills). But I have no idea why they dug it so deep, given that! Maybe to give themselves an (extremely) ample buffer for any future infrastructure in Manhattan.
- maxerickson 10mo ago
  The average depth is more like 400 feet. One diagram I saw indicated 2 different layers of bedrock. I didn't find anything real clear, but it can be that the lower layer is a more suitable material for the tunnel.
  - woodruffw 10mo ago
    Yeah, that's certainly possible for Brooklyn and Queens. Manhattan and The Bronx have very shallow bedrock, but Brooklyn and Queens have lots of clay, sand, and silt.
SoftTalker 10mo ago
The tunnel is a pipe, as long as the tunnel and exit end is lower than the entrance end, water will flow without pumps. Unlike an aquaduct, it doesn't need to be on a continual downward gradient from one end to the other.

nuccy 10mo ago

Rivers (e.g. Mississipi) work with much smaller gradient of just 0.01% [1], while with your assumption it would be 0.25%, so 25x. Maybe instead it needs to pass under the rivers [2: cross-section] surrounding New-York, which may be much deeper, especially when it comes closer to the bay passing Queens and Brooklyn [2: map] 1. https://en.wikipedia.org/wiki/Mississippi_River https://en.wikipedia.org/wiki/Mississippi_River 2. https://gordonsurbanmorphology.wordpress.com/2014/10/26/waterworks-manhattan/ https://gordonsurbanmorphology.wordpress.com/2014/10/26/wate...

woodruffw 10mo ago
This piqued my interest, so I checked: Tunnel #3 passes under the Harlem River and then the East River, but the Harlem River is less than 30 feet deep for the most part and the East River is around 40 feet deep at the most. (The Army Corps of Engineers has great detailed depth surveys for most of NY's waterways[1].) Edit: There's also a higher-resolution render of the tunnel layout here[2]. [1]: https://www.nan.usace.army.mil/Missions/Navigation/Controlling-Depth-Reports/ https://www.nan.usace.army.mil/Missions/Navigation/Controlli... [2]: https://extapps.dec.ny.gov/docs/water_pdf/nycsystem.pdf https://extapps.dec.ny.gov/docs/water_pdf/nycsystem.pdf

woodruffw 10mo ago

> I'd guess the reason for the 800 ft is because the reservoir it'll draw from is near sea level. I believe Tunnel #3 connects to the Catskill Aqueduct[1], which draws from the Schoharie and Ashokan reservoirs. Both are at least a few hundred feet above sea level (the Ashokan is about 600 feet above, since it was formed by flooding a valley in the Catskills). But I have no idea why they dug it so deep, given that! Maybe to give themselves an (extremely) ample buffer for any future infrastructure in Manhattan.

maxerickson 10mo ago
The average depth is more like 400 feet. One diagram I saw indicated 2 different layers of bedrock. I didn't find anything real clear, but it can be that the lower layer is a more suitable material for the tunnel.
- woodruffw 10mo ago
  Yeah, that's certainly possible for Brooklyn and Queens. Manhattan and The Bronx have very shallow bedrock, but Brooklyn and Queens have lots of clay, sand, and silt.

SoftTalker 10mo ago

The tunnel is a pipe, as long as the tunnel and exit end is lower than the entrance end, water will flow without pumps. Unlike an aquaduct, it doesn't need to be on a continual downward gradient from one end to the other.