Part of the Big Rivers project is the construction of dams. The dams should assist in controlling flooding and allow irrigation. I am not sure if they are also designed for power generation.
Perhaps they shouldn't be. In the western US, windfarms are becoming more popular and dams less so.
I'm torn on the issue. Certainly in the past, hydro-electric dams were the cleanest possible method of electrical generation. Nowadays, as they are perhaps less necessary, the problems, known, but minor compared to the other options, are becoming more onerous.
In the article linked above, dams interfere with salmon runs. That isn't such an issue here as, in Yangyang at least, salmon are collected as they enter the river and spawn in tanks at the hatchery.
Still, I am cautious about accepting President Bak's assurances regarding plans for the rivers after his trans-Korea canal scheme that was stopped.