http://water.usgs.gov/edu/earthrain.html
One inch of rain on one acre is 27,154 gallons of water. Imagine how much water we took in during this event. I live on 15 acres that received over 20 inches. That is 8,146,200 gallons of water. Now think about a 3,000 acre tract of land, 1,629,240,000 gallons. If Clarendon county is 696 square miles which is 445440 acres and if it averaged 18 inches that is 217,718,599,680 gallons of water.