Dump that much rain in that little time virtually anywhere, and there are going to be problems.
Harvey dumped epic, record amounts of rainfall. Period. There is a limit to what will soak in, what can run off, period. Put this on cliffhanger California, and it would all come out the wash--at the bottom of the hill. Put it on the prairie, and a levee will likely breach somewhere, put it in the mountains most any place, and the valleys will fill. It's just too damn much water dumped on anyplace on land for normal drainage to cope with.