Dams hurt rivers, but are rivers more important than children?
September 7, 2014 8:00 PM   Subscribe

How do dams hurt rivers, exactly? Is that damage built in – that is, are there ways to mitigate it? On the other hand, do a few million people deserve electricity? Looking for reasoned arguments. Caveat: solar power is reasonable, but I don't see it replacing the Aswan dam in the next few generations.
posted by LonnieK to Science & Nature (18 answers total) 4 users marked this as a favorite
 
Smart people disagree about this, so don't expect to get one clear definitive answer.

Short answer: dams are bad for rivers, but great for people, but with caveats for both parts. They are bad for rivers because they impede natural function and block upstream/downstream connectivity for sediment and organisms, as well as radically changing the hydrograph. So instead of a big pulse of floodwater carrying sediment, all that gets stored in a reservoir behind the dam, the sediment building up and the water used or released slowly.

That's terrible if you are a salmon or other migratory fish, or an ecosystem that relies on those regular flood pulses, but great if you are bilharzia/schistosomiasis (helped by the Aswan high dam, in fact) or any number of other invasive species that like warm, stagnant water. Which gets at the cost/benefit question -- the benefits of electricity, flood control, irrigation, and transportation are obvious but the costs don't always show up immediately.

Fundamentally, the benefit of dams is civilization itself, starting with water supply and irrigation -- we wouldn't be here without that. But the ecological costs are extensive and have to be paid somehow. Also, there are absolutely better and worse designed dams in terms of lifespan, mitigation for impacts, and providing maximum benefits for the costs.
posted by Dip Flash at 8:47 PM on September 7, 2014 [8 favorites]


Well, if we're thinking in terms of human impact, damming a river for electricity irrevocably changes the water access of people who are what used to be downriver. A good example of this is the current controversy regarding the Gilgei Gibe III dam Ethiopia is building on the Omo River. Great news for Ethiopia, but it cuts off the main water source for Lake Turkana in Northwestern Kenya, threatening the populations that rely on it for survival. Here is one summary of the situation, and a more detailed article (pdf) that goes through the complexities and potential sources of damage.
posted by ChuraChura at 8:54 PM on September 7, 2014 [2 favorites]


If you don't mind a historical look at some of this in the US, you might like to read the last section of Encounters with the Archdruid which is written by John McPhee and basically has a noted environmentalist (David Brower) and a noted dam-building government employee from the United States Bureau of Reclamation (Floyd Dominy) having a pretty open debate about the benefits and disadvantages of dam-building. A very good read. There are no easy answers and even asking "Are rivers more important than children?" is really overlooking a lot of the nuance in just exactly what is problematic about river damming at the large scale that it happens at now.
posted by jessamyn at 9:00 PM on September 7, 2014 [9 favorites]


Agreeing with Dip Flash, it's incredibly complicated and often provides relatively short term benefits with potentially unknown costs.

In your example of the Aswan dam for example, the change in the flood cycle is resulting in increasingly challenging soil conditions in the fertile Nile valley. Pollutants and minerals that would normally be washed into the river on a regular basis are now accumulating instead and it's becoming increasingly challenging to maintain the same yields.

And of course the fact is that in many countries, such as Egypt, the infrastructure needed to move the power is decaying rapidly, which means that people aren't really receiving the benefits at this point anyway (my in-laws have been without power 3-4 times a day all summer).
posted by scrute at 9:03 PM on September 7, 2014 [1 favorite]


The most important change has to do with silt. Rivers naturally carry silt, and deposit it downstream, or eventually into a delta in the ocean. A dam stops all that; the water reaches the lake behind the dam and sits, and all the silt settles out. Beaver dams do exactly the same thing, on a very much smaller scale, and when the pond behind a beaver dam silts up completely, the result is a meadow. (And then the beavers move on.)

In some places the loss of yearly silt has been catastrophic (Aswan High Dam, I'm looking at you). But just like a beaver dam, the big problem is that eventually enough silt will collect behind the dam to render the dam useless for things like hydroelectric generation. Dredging may be part of the solution, but I'm not sure anyone has a complete answer.
posted by Chocolate Pickle at 9:07 PM on September 7, 2014 [2 favorites]


Framing it as rivers vs. children seems like odd framing. I don't think anyone really cares if dams hurt rivers. People do care about crop yields, changes in water distribution/access, the people who used to live where reservoir ends up, pollution, invasive species, and other ecological damage that affects the fisheries, public health, and the local economy. These things don't make the river spirit cry, they change people's lives. And while a lot of these things can be mitigated or worked around for a price (fish ladders, relocation, environmental management, etc.), it comes down to a cost/benefit analysis.

But it isn't even that easy, because different people bear different shares of those costs and benefits. The creation of the dam should ideally not just be a net good, but also fair. Hurting one group of people to help a different, larger group isn't unambiguously good.

So its more of a discussion about this child being relocated (which child?), that child getting malaria (which child?), many of them having better access to electricity and all of the accompanying benefits (but again, those benefits not being spread evenly or according to burden), the price of water for them changing, many parents changing jobs (less farmland, less fish, less tourism, more construction, more industrial), and all of them having a slightly higher food price.
posted by Garm at 9:55 PM on September 7, 2014 [5 favorites]


Caveat: solar power is reasonable, but I don't see it replacing the Aswan dam in the next few generations.

Now, I might have my figures totally ass-up, but it appears that the Aswan Dam produces 2.1 gigawatts of power daily which would equal roughly 800 Gwh per annum. Yet Germany, which is so much farther north than Egypt and thus receives less sunlight, produces 29000Gwh per annum via photovoltaics and a staggering 47000Gwh of power from wind energy.

It is quite likely that I have made a megabit/megabyte mistake in my reading, and I would be happy to corrected on those figures, but the notion that it is going to take a few generations for technology to provide alternative power sources is simply false.
posted by salad at 10:06 PM on September 7, 2014 [1 favorite]


Your problem is mixing up a unit of power with a unit of energy. The Aswan Dam produces 2.1 GW of power. That means 2.1 GWhour of energy every hour, or 50 GWhour per day, or 18,400 GWhour per year.
posted by Chocolate Pickle at 10:46 PM on September 7, 2014 [2 favorites]


Dredging may be part of the solution, but I'm not sure anyone has a complete answer.

Dredging is unlikely to be practical. For example, the Glen Canyon Dam on the Colorado collects 45 million tons of silt a year, an average of 85 tons a second. That's roughly one coal car a second, 24 hours a day without stopping, just to keep up with new deposition, let alone reducing the 50 year backup.
posted by JackFlash at 11:09 PM on September 7, 2014 [1 favorite]




There are a lot of problems with phrasing this problem as: "Are rivers more important than children?"

First, there are usually people both upstream and downstream of the dam, and the people downstream are often hurt by the dam (see farmers in Mexico who used to rely on the Colorado River for irrigation) while people upstream profit. So a more accurate question would be: "Are these children more important than those children? How many children downstream do there have to be before they're more important than the children upstream?"

Secondly, dams are usually used for multiple purposes, and at least two of those are often at cross-purposes: hydro-electric power for cities and water storage for agriculture. In order for the dam to create the most hydro-electric power, it should be filled to the top at all times, with additional water being let off as run-off. In order for the dam to store water for agriculture, the water level should vary: in the winter it should be lower, so that it can catch all of the water from the spring floods, so that that water can be used later in the dry season, when the crops are at their height. Because most people can't agree on which use gets priority, they often compromise and keep the water level (when there's enough water) in the middle, which means that most dams do not function efficiently. So another question you could ask is: "Is electricity more important than vegetables?"

Finally, that last question might sound a bit glib, but here's the thing: dams also allow people to live in arid places where they wouldn't otherwise be able to live (and where they maybe shouldn't live). The American West used to be called "The Great American Desert" until the 19th century brought the Industrial Revolution along and allowed people to drill for groundwater and build big dams. Groundwater is a non-renewable resource, although we tend to use it like it is renewable, and the climate is changing, which makes droughts more common and more severe. So people in those arid areas are going to have to start making decisions about what is more important: electricity or vegetables, cities or farms. No matter what, people are going to be harmed, which means the question isn't just: dams or children?
posted by colfax at 1:58 AM on September 8, 2014 [2 favorites]


Well, if we're thinking in terms of human impact, damming a river for electricity irrevocably changes the water access of people who are what used to be downriver.

It also damages people upriver since what used to be a river will now be a much bigger reservoir. So there are costs for relocation and infrastructure and significant damage to social capital. The Three Gorges dam required the relocation of millions of people.

This page lists the social consequences of just the Three Gorges dam. "The 400 mile long reservoir of the Three Gorges Dam has flooded 13 cities, 140 towns, 1352 villages, and 100,000 acres of China’s most fertile farm land."
posted by biffa at 2:02 AM on September 8, 2014


I don't think anyone really cares if dams hurt rivers.

As has been noted, this is not true. Scientists and environmentalists care, the people who prefer to raft or fish on wild rivers care, and the mostly ignored indigenous populations usually care a lot.
posted by Dip Flash at 6:19 AM on September 8, 2014


pracowity: "I don't think anyone really cares if dams hurt rivers.

Lots of people care if dams hurt rivers.
"

Dip Flash: "I don't think anyone really cares if dams hurt rivers.

As has been noted, this is not true. Scientists and environmentalists care, the people who prefer to raft or fish on wild rivers care, and the mostly ignored indigenous populations usually care a lot.
"

You both seem to have glossed over the rest of garm's post, and may largely agree with them. My reading is that garm is distinguishing between hurting the river (you can't - rivers don't have feelings) and the consequences of damming the river (positive and negative), which can hurt people and the environment.
posted by zamboni at 7:43 AM on September 8, 2014 [3 favorites]


FWIW, many to most of the indigenous people who live in the Athabasca Delta region still get most of their food and income from the land. This is an area that has been impacted by the W.A.C. Bennett Dam and may soon be impacted by the Site-C Dam (not to mention the Tar Sands and climate change).

They care very much about their health, environment, history and way of life. Canadians mostly think that colonialism is over but it's not, by a long shot. Hydroelecticity is one of its blunt instruments.
posted by klanawa at 4:44 PM on September 8, 2014


My reading is that garm is distinguishing between hurting the river (you can't - rivers don't have feelings) and the consequences of damming the river (positive and negative), which can hurt people and the environment.

The river is an integral and central part of the environment involved in damming. You contradict yourself when you say that it is impossible to hurt the river but possible to hurt the environment.
posted by pracowity at 2:03 AM on September 9, 2014 [1 favorite]


I apologize, let me be more clear. I think the framing of 'the river or our children - pick one' is bad. All of those things that 'hurt the river' are bad (including the listed flood risk, greenhouse gas emissions, lower water tables, removal of navigation routes, inability for a culture to continue, etc). But those things are not abstract. They are all bad for other children.

If the rhetorical framing of 'cute child vs. inanimate object' remains, cute child will win every time, no contest. If it is instead framed as 'these cute kids will be better off in these ways vs. those cute kids who will be worse of in those ways, also all of the kids are in both categories, also these cute kids who really paid the largest cost and were realistically never going to benefit anyway', then the question is more likely to be answered thoughtfully.
posted by Garm at 11:20 PM on September 9, 2014


But those things are not abstract. They are all bad for other children.

Thanks for the clarification. I don't want to turn this into a back and forth at all (which is both boring and against AskMe rules), but as part of deepening my previous answer to the question I will note that there are really are people who are focused entirely on the functionality and holistic health of the river (or riverine ecosystem) rather than the impacts on humans. That is what is funding my work and what is guiding the entire organizational mission, and as a consequence we are able to do some really interesting and long-term projects (including small dam removals) that wouldn't be possible if we were working just on the externalities affecting humans.

But at the same time you are correct, the wider legal and social environment is concerned almost entirely with the impacts on humans. Getting larger projects accomplished (especially dam and levee removals) requires endless discussion and compromise, and finding ways to mitigate potential human impacts -- you can remove a levee, but only if you can do so without increasing flood risks to adjacent landowners, for example. Projects that are great ecologically will still routinely be blocked or reduced out of concern for those impacts, real or imagined. And this in the US, which has strong laws (e.g. ESA) forcing consideration of those non-human impacts; in most of the world, decisions about building dams are done with basically zero consideration of environmental or other long term costs.
posted by Dip Flash at 7:05 AM on September 10, 2014


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