You got a good machine for creek hunting. How to set it up properly is not an easy thing to explain here due to the multitude of variables in your area. Your best bet would be to check some of the Whites exclusive web sites. I think there's one here on Finds. For more detailed help, drop an email to Jim McColloch at ophirau@msn.com.
He's one the most well versed in it's operation and could probably give you some good pointers for your area. It looks like you may be in Virginia. I don't know of anyone here who is familiar with your conditions out there.
At any rate, tell Jim that Digger Bob asked you to contact him and see if he can help you out.
Digger Bob