NYC should be designed to easily handle 15" / hr downpour. The 3.5" dumped by Ida should have been nothing- unless the drains are clogged with trash. You can see large trash cardboard/paper debris floating in knee high flood waters in places like Queens. Junk like that either clogs the street level grate or the storm drain itself with enough accumulation. Then this stuff with large swaths of flooded areas filled with standing water for days- obviously gravity isn't taking the water anywhere- the drains are all clogged- the water just stands there until it evaporates or percolates into the ground. The entire incident was a result of municipal negligence in maintaining their storm water runoff system.
De Blasio micromanaging stuff he knows nothing about, again: