Big hydropower dams are not only hugely destructive while being built, they have disastrous environmental consequences after completion.
Scientific American details the Three Gorges Dam Disaster in China in a 2008 article citing problems like less rain and more droughts, increased chance of earthquakes and landslides, and potential for spreading of disease.
The vast weight of water in the 410 mile long, 510 feet deep lake behind Three Gorges dam (or behind any huge man-made lake) forces water deep into cracks in the earth. When the water level drops because of dry conditions or releasing water, the weight lessens. Water pressure in the underground fissures drops. This can trigger earthquakes like those already documented at Oroville Dam in California. Additionally, the huge weight of water against the land enclosing the lake causes landslides and huge fissures.
Biodiversity is threaten by these huge dams (of which Three Gorges is the biggest) and of course hundreds of thousands of Chinese have been relocated, sometimes multiple times, as new landslides and fissures keep occurring.
The most alarming effect of big hydro is that it changes the weather, causing drought, as has happened with the Guri dam in Venezuela. The Chinese government denies Three Gorges has caused drought, but the evidence seems to prove them wrong. This is the ultimate unintended consequence. The dam was built to product hydroelectric power but by its very construction causes droughts, lessening the amount of water to create power with.
Yet governments blunder on. Brazil just approved the Belo Monto dam, which will be the third-largest in the world, displacing 20,000 people. This time will be different they presumably say. Or maybe they don’t much care what happens so long as some electricity gets generated for their hungry cities and politically connected contractors get huge contracts.
So, I wonder, if big hydro has so many unintended consequences, what will be the unintended consequences of installing solar power on tens of thousands of acres in California? Because there will probably be some. We think we understand and can control nature, but I’m not so sure we can.