Do your due diligence on the legality and availability of videoing around dams. They are very **** about the infrastructure around dams.
Even with a 107, several friends of mine have yet to get permission to survey dams or power stations with their drones, and they are electricians working for the company who owns said structures. (Southern Company)
FAA will have no issue with flying if you have owner approval, so you will be good there.
The only issue will be the guidelines you'll have to hash out as to where exactly you'll be able to fly. If they already want to pay you to do the footage, then they already have an idea of where the off limits areas are.
For example, any power transmission lines and towers will be off limits, due to liability, and flying over an intake pipe or similar would also be prohibited.
Basically, any educated fool knows not to fly over somewhere that would potentially cause damage to facility if you were to lose power and drop out of the sky.
My work has a drone we use to fly for surveys and such, and there are several areas we are not allowed to fly it, like directly over the stack of any powerhouse boiler! Duh!
If they let you, I would love to see some footage, especially if they are dumping water or an overflow is active!