Like several states in the southeast, Georgia is mostly clay. The dirt here (if you want to call it that) is bright reddish orange, very fine, and packs densely. It it can be molded into shapes and fired in a kiln to make pottery. As such, it does not absorb or leach water very well. So when the low pressure system stalled, the rains came... and didn't stop.... for days. The ground absorbed what it could, and the rest flowed over the ground and into streams, seeking lower ground.
Streams swelled their banks and the water kept rising. The
news coverage described the devastation. To get a feel for how bad it was, there are some videos
here and
here. Having seen the videos, it doesn't come anywhere close to seeing it with your own eyes. For a side by side comparison, here is an area that is about 100 yds from the banks of stream during the flooding and a day later after waters receded:
Current
http://photos-a.ak.fbcdn.net/hphotos...4_502438_n.jpg
Normal:
http://photos-b.ak.fbcdn.net/hphotos..._3969681_n.jpg
I also posted my own personal video
here. That stream is normally 3-4 feet wide and 20 feet lower...