Justin-
Your Spring at the head of the gully is probably a tile drain coming from under the adjacent farm fields. No big deal, I just wouldn't depend on it for consistent flows.
I also like temporary "natural" blinds but the deer always manage to find the holes in them. For semi permanent blinds I have gone to using sections of cattle panel wrapped first with black sheet plastic and then with burlap. They are less expensive than Pop-up blinds and wind, rain, sleet, snow... and COWS can't hurt them. They don't take any longer to put together than cutting and dragging brush would and last a whole lot longer. Unless you really go to town with the construction, natural blinds rarely have tops and I don't mess with roofs on my panel blinds.
Don't buy new panels unless you just want to. In my experience there isn't a farmer or rancher in America that doesn't have a few rusty ones (I see CAMOed, rather than rusty) laying around and the smell is pretty much knocked off of them. You can probably get them just for the service of hauling them away or if the farmer is thrifty, buy him a couple new ones and trade for the weathered ones. I'm happy to go into a little more detail if you would like to know how I build the panel blinds.
Sounds like you have your new obsession for the Fall! Good luck!
OkKeith