This looks like a reasonable site. First, you need to know what the subsoils are really like. Is there any clay at all?
If there is no clay, a liner may be a good idea.
Engineering is important simply so to know how tall, how wide and how strong it should be. A dam is a water control device. Its job is to receive water, impound it, control excess water, then release it in an orderly fashion. Engineering helps design a spillway, determine the need for a pipe, etc.
The follow up to this is to start by contacting the NRCS (Natural Resource Conservation Service) in the USDA building in your county seat. They can either help engineer the dam or steer you to someone who can.
There's some starting points for you.
