I live a couple miles south and there has been too much development in the watershed in that area. Forests cut down and paved, farm land built up and paved. There are stormwater management rules now but the developers know how to get around them. My mom is in a development that is dealing with clogged drywells and incorrectly installed storm water controls. No one inspects these things while they are being built and by the time you realize they aren't working as intended its too late.
The downtown area would still flood, but not to this degree. At this point it might be worth it to build some sort of elevated board walk on stilts. Close the road to traffic and only allow businesses in the 2nd+ floors. Or get Elon Musk to bore a huge tunnel underneath. I know DC is building huge underground tunnels to store excess storm water.