The ideal big dam is Hoover Dam. Large, deep canyon in a desert. Narrow, deep canyon dam site. Hard rock geology. No major towns or agricultural areas in the area to be flooded above the dam. That's the best case.
Except now thanks to climate change the water levels might drop below the intake in lake Mead. Lake Powell is even worse, Glenn canyon dam was always a mistake, and it might stop producing power next year.
The ideal big dam is Hoover Dam. Large, deep canyon in a desert. Narrow, deep canyon dam site. Hard rock geology. No major towns or agricultural areas in the area to be flooded above the dam. That's the best case.
Most later dams are at worse sites.