You apparently have your city map turned upside down. Your responses make no sense at all, I mean when you ask how a retention basin can prevent flooding, I really don't know what else to do with you. That's the purpose of a retention basis, after all. It holds the water so as NOT to flood what's downhill from it.

The detention in City Park is for the Montclair Basin, which already naturally flows through there. The Park Hill basin will be draining into Sand Creek. And no, the drainage in the basin south of MLK does not in any way flow south. You really need to study up on this some more.