Goulds or Waterpumpsdirect have a ton of pumps that will move the amount of water you need> 18 gpm really isn't too much, you could probably pick up a pump at a local hardware store that can move that kind of water.
Bradley Dennis
Civil Engineering
http://culvertpipe.net
http://www.worldclimate.com/cgi-bin/data.pl?ref=N33E044+2100+40650W
Has some very sparse information.
Bradley Dennis
Civil Engineering
http://culvertpipe.net