[ghshephard]

I was the original poster suggesting the Tokyo System - but I did the math and I was wrong.

The total underground capacity of the Tokyo consists of the Cans, (250K cubic meters), Cistern (248K cubic Meters) and Tunnels (575K cubic meters) - for a total underground capacity of 1.07 million cubic meters.

New York City was hit by 35 Billion gallons of rain during the flash flood, which = 132 M cubic meters. The Tokyo System has .38% of the capacity of the rainstorm, and is capable of draining at 200 cubic meters/second which would take 7-8 days to drain all that water.

What happened in New York was epic - and no underground system imaginable would have been able to handle it. The only solution to this type of problem occurring in the future is going to be around things like zoning (don't build where it's going to flood), landscape (lots more greenery), architecture (lots more void decks, first floor resilience to flooding, no basement suites, etc...)