Jeannie, do you think rainwater is running
off your land? Or to somewhere where you don't need it? Or better question, what is happening to the rain currently?
How much rainfall do you get, and what are the longest times between decent rains?
Do you have a water take?
I agree with Blake, land is rarely completely flat. There are some resources in this thread on swaling on flat land
http://permaculturenews.org/forums/forum/permaculture-forums/designing-building-making-and-powering-your-life/7739-flat-land
To find out the contours on your land you can survey it yourself using an A frame. Google 'A frame swales' and you will get many instructions. Or find a local permies or surveyor who can teach you, it's not that hard and you can build/find the gear necessary locally without buying expensive equipment.