Yes, its a big deal. City and county planning tend not to account for these - or willfully ignore. FEMA doesn't care other than "navigable waterways", they just amend the maps later.
They have put in place strict laws around here about what percentage of the ground of a lot you can cover. Builders dig out swampy areas to create retention ponds so they can sometimes get "exceptions" to the rule. It usually ends poorly. A normal rainstorm downtown will put a foot of water in the city streets. Over hundreds of years Charleston has figured this out and built accordingly - using the streets as storm drains. Other places don't have this tribal knowledge.
