Sounds awesome Double!
Good thing diesel is so cheap right now when you are going to be moving all of that dirt.
Possible negatives would be hitting a bedrock layer while excavating your deep bowl for usable clay. If so, you can probably borrow clay by not excavating as deeply, but taking from a broader area. Stay away from loose rocks or rock layers.
Since your final shoreline (at full pool) is literally your choice at this stage, are there features you would like to incorporate? For example, some rock ledges at the water's edge, or some big humps you want in 8' water to put bass structure on?
You might want to buy or rent a surveyors transit level. (Inexpensive unit with full accessories kit is less than $300 at "big river in Brazil". You could rent an even nicer one.) I use mine frequently on the farm.
You can set up on your lower ground and just rotate your turret and evaluate different shore line elevations. You don't even need to have your construction bench mark set yet, just make relative observations. Be sure to flag the features you want at full pool elevation. Pick the level you want that has the most of your favorite features at the preferred depth.
Once you pick a optimal shoreline elevation, be sure to have the professional surveyor confirm when he sets the benchmark for your dam construction. Your survey will have some small errors for your measurements over a few hundred feet with that quality of equipment.
Just throwing out some ideas while you are still in the planning phase.
Good luck on your big pond project. 13 acres in Texas sounds like a dream!
