Just to clarify some of your dam design information.
1. Proposed finished dam height is about 30 ft.
This is tall for a structure in most States.

2. Proposed freeboard (height above Principal spillway or tubes) is only 1 ft.?
Consideration should be given to future settling, erosion, wave action, etc. I wouldn't go anythin less than two ft. and probably three ft. would be better.
3. Propose using 6" tubes opposed to 12" tube?
A 12" tube would be a minimum as mentioned by others on this forum. A 6" pipe will easily plug; Also each tube should have at least one anti-seep collar installed.

4. Proposed emergency spillway is concrete spill over top of dam?
I guess I would prefer to go around the side of the structure with an earthen emergency spillway. How much concrete were you going to use?

Just my $.02.

Ed