This blog is all about slowing down water so it can soak in, be used, saved, and enjoyed. Rain gardens, rainwater cisterns, natural and created wetlands, and healthy riparian forests all help us attain this task. But what about huge dams and the reservoirs behind them. They also slow down water... do they help us conserve water and act as responsible land stewards?
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This is a difficult question, and one I've struggled with. As someone who loves rivers, I dislike large reservoirs for the simple reason that they bury free-flowing rivers under millions of gallons of water. It may be that we needed to sacrifice many of our most beautiful, beloved rivers (as we did over the last century) so that we can generate power because the alternative is even worse. Or, it may be that the big dams aren't earning their keep. Recently I came across this article, which argues that in terms of greenhouse gases, reservoirs may not be all that much better than fossil fuel energy because the large lakes behind dams lead to the release of methane. (In addition, though not mentioned in the article, large tracts of riparian forest are also destroyed by these reservoirs).
I'm not sure if I am convinced that the methane released from a reservoir is as harmful as the emissions from a coal power plant... but there are many other issues with dams and large scale hydroelectric power, as well. As mentioned above, we've lost a lot of riparian forest and wetland behind all our dams. It also takes a LOT of energy to create a large dam, and they definitely do not last forever. In the long term, all reservoirs fill with silt, and in cases of degraded watersheds (which probably includes most watersheds above US reservoirs) siltation can happen surprisingly fast. Once a reservoir fills with silt, there is no way to fix it other than dredging at massive expense.
Reservoirs aren't just created to generate power, of course. They are also created to hold back water during wet periods and release it during dry periods. Unfortunately, evaporation from reservoirs results in loss of a massive amount of water to evaporation, especially in dry areas at the highest risk of drought (such as the Colorado River watershed). Reservoirs may decrease the magnitude of flooding, but they haven't necessarily decreased the impact of flooding on people, because once we built them, and the floods decreased in magnitude, we built homes in flood plains; people still face flood damage any time there is high water. Flood-control dams struggle to hold back water and silt above Los Angeles so that the concrete ditches draining the city aren't clogged, and we are running out of space to put the sediment that collects behind these dams. Meanwhile many fisheries have collapsed due to the obstruction of fish migration by dams, and invasive species have exploded in population where natural flood regimes have been altered.
Essentially, we destroyed wetlands, beaver meadows, and flood plains, then created giant reservoirs, at massive expense, to do what these natural resources were doing for free - decrease floods and drought. In return we gained some space for permanent structures in flood plains, but we also lost massive amounts of space when we flooded large areas behind the dams. Was it worth it? Could we have used our time and effort to develop something else that could have worked better? Could we have instead farmed around the flood cycle the way the ancient Egyptians did, and allowed the rivers to do our fertilization for us?
At this point we can't get rid of all our large reservoirs without coming up with energy elsewhere, and without restoring large areas of watersheds (though we should do that anyway). Still, I feel like we are running into the same economic and cultural issues we are running into as we work to find other forms of alternative energy. Instead of building solar panels on every south-facing rooftop and placing windmills on the edge of farm fields, large corporations are pushing to bulldoze vast areas of the desert to build large solar farms, and scraping off ridgetops for lines of windmills (and transmitting the energy inefficiently from these places to populated areas).
There may be a time and a place for large-scale developments like these, but I can't help but think that the best solution is more local. A lot of small-scale hydroelectric power generation could take the place of our larger dams, over time.
I'm also slowly becoming convinced that we need to look much more seriously at high-tech, small scale, safe nuclear power generation. 1960s style plutonium fission, as seen in Fukushima, Chernobyl, and Vermont Yankee, are clearly not worth the risk. But, there are many other options if we look past the word 'nuclear' and are creative and cautious. These high-tech, small-scale power plants are incredibly different from our large, aging, leaky power plants from the 1960s. We don't use solar panels from the 1960s (were there any?) so why use nuclear technology from back then?
What do you think? Are our big dams worth the downsides? Or should we be working to slowly get rid of them? What do we need to sacrifice to survive as a society into the future? These are hard decisions, but there are also some great ideas out there, and I remain cautiously hopeful.