Bottom line is there are a few little things that create an issue with drainage. High tide, a lot of the area below sea level, around 2.5" of rain according to my gauge, you don't have to dig far to hit the water table, I'm less than a mile from one of the inlets/outlets to the ocean...pump for your backyard? Holds water because it's too flat?
I dropped a sump-pump basin in a few years ago along with a sump pump...a lot of 1.5" PVC underground that runs to the street...pumps 3650+ gallons per hour. I turned it on when I got home this morning (3'ish) and it is still running a little. And, there's still a little water back there.
When I left downtown this morning there are a half of a dozen or so streets closed and they'll be that way for another hour or so.