Hydro plant failures have ocurred, and are far and away the most lethal energy-related accidents to date, true. The worst power plant accident of time, not a nuclear power plant failure, but a hydro station in China, Banqiao Dam.
It's instructive several ways.
Any number of fairly simple methods would have hugely alleviated the impact of the disaster. Much as with major nuclear disasters, it was a cascade of failures, starting with poor management and a dysfunctional culture, amplified through poor design, adverse conditions, poor communications, delayed or absent warnings, and little or no disaster response (many of the deaths were attributed to starvation and disease, not drowning or other physical impacts).
A useful thing to keep in mind, though, is that after a dam break is done being a a massive disaster area, which typically resolves in a few hours to a few weeks, the land is no longer a glowing radioactive mess. It can be re-settled and populated as structures and infrasctructure are rebuilt. Zhumadian City, the region surrounding Banqiao, has a present population of over 7 million.
Hydro disasters have been large, but are tangible/sensible, immediate, and resolve relatively quickly.
There are literally tens of thousand of dams, if not > 100k, worldwide (over 22k in China alone), with well over a century of major utilisation. Granted 100 or fewer major (2+GWe) installations.
There are fewer than 400 nuclear power stations worldwide, with at least three highly notable failures.
The immediate innundation from Banqiao was responsible for ~25k deaths. The additional 100k or so came from starvation and disease due to widespread disruption of the region, and a grossly inadequate disaster response plan and capability. Adequate engineering, operation, management, forecasting, disaster planning, preparation, and response, could have reduced the loss still further.
Organisational / institutional failures at Chernobyl, Fukushima, and for that matter, Hanford and Sellafield, were and are massive contributing factors. These cannot be engineered around.
