When that elaborate mechanism was triggered I was like
wait a minute, there were Freemasons in Middle Earth?
I also had a flashback to the most recent
Tomb Raider movie, when Lara deciphered the puzzle on the outside of the cavern where Yamatai's tomb was hidden. She aligned a series of tumblers and then the wall of the cavern collapsed to leave a gaping hole. What was hilarious about that was one more well-placed explosive would have accomplished the same thing lol. Which leads me back to your question: How would Adar & his orc followers destroy the dam without the use of some kind of Macguffin and/or the aid of dark magic? It's not like they had a supply of C4 or anything else with the firepower necessary to accomplish such a feat. That dam was massive.