I do think that dams look awesome. But of course you shouldn't build them to make the landscape look nicer. Especially today, more dams should be built, both to ensure water supply and as the ideal support for wind and solar. Dams are the cheapest form of mass energy storage - many of them can even run "reverse" and store surplus energy by pumping water up into the dam.

A lot of people, including me, think the exact opposite: we should be tearing down as many existing dams as possible. Dams are extremely damaging to river ecosystems and are a huge contributor to coastline erosion and exacerbate droughts.

http://news.nationalgeographic.com/2016/11/dam-removal-nelso...

One has of course to learn from the mistakes of the past when deciding where and how to plan and manage dams. But California seems to suffer alternating from floods after the snow melt and droughts in between. The current dam infrastructure is to buffer the floods and release the water at a more constant rate through the season. I cannot see how this could create droughts.

Here in Germany we traditionally have more water than we need, but recently the weather is more extreme. We get stronger rains in shorter times, leading to flooding and times with less than usual water. More dam capacity is the obvious solution to that.

Preferably, dams should not be built in the middle of a living river system, but higher up in the mountains, capturing the seasonal water. Also, where needed, small bypass rivers should be kept, allowing fish to migrate freely.

Dams contribute to droughts by limiting the recharge of downstream ground water levels and aquifiers.

Can you explain why? Over the year they would release the same water as the river without the dam would do - just not in a peak flood but reduced to a constant flood rate.

Dammed rivers release less water because of increased evaporation. Another problem is riverbed deepening which lowers the groundwater table. Where the water pools up is also important - having a bunch behind a dam when former wetlands and floodplains are dry is obviously not conducive to the ecosystems in those wetlands and floodplains.

Doesn't that all very heavily depend on the exact nature of the system the dam is part of? We all know of the environmental problems of the Assuan dam in Egypt. But that does not mean that properly planned dam cannot be very beneficial. One shouldn't just build a dam where it is convenient but with careful analysis first. There are plenty of places where a dam just means less cities flooded occasionally but otherwise has little eco system impact.

Why do dams increase evaporation? Having the water all in one place as opposed to distributed over the length of a river should reduce surface area.

You're talking about Hetch Hetchy and the O'Shaughnessy Dam? Environmental impact is one thing, but it wasn't built to "look beautiful and bring more people out to nature," which is ridiculous. (Advocates may have claimed this, but it was not the motivation of the project.) The dam generates electricity and the reservoir provides 2 million people with water, including San Francisco, the latter of which is was the main driver of the project.

If you read the old literature on how controversial it was at the time, those supporting the dam said it would increase the leisure use of the site, giving it a great lake to camp and fish at. They literally believed it would improve the natural surroundings.

Even modern say SF offices still use that line: "They were eager to show us how, they say, the reservoir actually enhanced the beauty of the valley,"

http://www.pbs.org/newshour/bb/environment-july-dec05-dam_8-...

I didn't say it was the motivation of the project, just that it has been claimed and used to buttress other arguments.