Gowanus Watershed With 1766 Marshes and 2013 Sandy Flood Line
Sandy essentially flooded anyone who built on the former tidal marshes.
Map Explanation by mapmaker Eymund Diegel:
Red lines are the upland Sandy flood lines (minus part the Fort Defiance Island area which is missing dry non flood area during Sandy)
Light blue lines are the expected direction of rainwater surface runoff flows, assuming that all storm drains are clogged or backed up
The dark blue line is the topographic watershed limit, and green is the historical (now landfilled) tidal marsh.
If it rained heavily for 3 days, you had flood storm surges, as well as heavy winds with leaves clogging drains leaves and trash, the streets marked in blue would most likely have flooding issues (even if they are out of the red tidal surge flood zone)
The runoff model is based on existing land slopes (topography) and is similar to upland storm flood modeling done for Zurich Switzerland and Berlin Germany.