No dams were demolished in the making of the true story upon which this movie is based.
There was a story in the Los Angeles Times in 1972 about a Peruvian engineer whose son was kidnapped by a band of Indians, and of his successful search to find the boy. I haven't tracked down the story itself (the online LA Times doesn't go back to 1972, and I'm not curious enough to trot down to the Central Library), so that's all I know.
I tried looking up the dam on wikipedia but it says nothing about it ever collapseing. Remember, nobody knows that he was trying to blow it up so even if it is a true story, history will say the dam collapsed, it was not blown up.
Also I don't see how he was going to blow through 50 feet of concrete with 10 sticks of dynamite. In WWII they tried to destroy dams in German with 5000 pound bombs with mixed results.
In the true story, the father was not an engineer, he was a lumber man. So there was no dam involved. And he wasn't American, he was Peruvian. You can see the original newspaper article here: http://www.nativeamericanfilms.org
Harlan Ellison gives more background on it in his book "Harlan Ellison's Watching". The film was almost entirely made up of whole cloth. We can't even be sure it was the Mayorunas because anthropological journals keep track of that tribe very carefully and none have mentioned an adopted outsider.