Be cautious of the NRCS...about 10 years ago they said my new pond would never fill up. Well, its been full ever since.
Some of the best data is your neighbor's ponds. If they hold water, then the chances are very high that yours will also, if its built right. Ask them who built theirs and then contact that person with your questions.
Thanks for the heads up regarding the NCRS. My neighbors ponds have all been around for 20+ years. I had a guy come by that does pond work and he is confident he can build a dam in the ravine. My main concern is water flow, being sure there is enough water running through the ravine to adequately maintain a healthy pond.