I remember seeing posts here that had a few web links to what you're looking for Ed, you may be able to "search" them up. The site I use is http://terraserver-usa.com
It takes some digging around, but surface & topo maps are there. Should assist with watershed area.
For pond construction, runoff, and overflow...you definately need a copy of this :

http://wildlife.tamu.edu/publications/590hb.pdf