
Reservoirs are contributing 1.5% of global greenhouse gas emissions - Osiris30
http://reflectionsonwater.org/blog/2016/10/7/damwho-knew
======
brownbat
A lot of rice production involves standing water (and the burning of rice
straw between seasons), and so rice farming is a major contributor to GHG
emissions:

[http://www.southasia.ox.ac.uk/sites/sias/files/documents/GHG...](http://www.southasia.ox.ac.uk/sites/sias/files/documents/GHG%20emissions%20from%20rice%20-%20%20working%20paper.pdf)

It also happens to be a staple for over 60% of the world's population. And
unlike transportation and energy, obvious substitutes are much harder to
identify.

The more I read about novel sources of GHG the more intractable this problem
appears absent geoengineering.

~~~
Fej
Global warming is going to require a massive, species-wide effort to
counteract. The problem gets worse every day. When do we decide to stop?

We're already pretty far gone. Now it's a matter of controlling how Earth-
shattering the damage is.

------
heisenbit
I found this article confusing:

>There are three main differences between man-made reservoirs and lakes:

>1\. Man-made reservoirs require flooding terrestrial land, supplying a large
pulse of dead organic matter from trees and grasslands. The timescale of how
this happens to natural lakes is much longer.

>2\. Man-made reservoirs experience greater fluctuations than natural lakes.
As reservoirs reduce in volume, the weight of the water over the sediments
drop freeing even more methane molecules from the confines of their origin.

>3\. Man-made reservoirs are often closer to human activities, such as
agricultural run-off containing fertilizers that can promote the growth of
organic matter in the water.

Here one-off effects are mixed with ongoing effects which makes limited sense.
Also agricultural run-off is mixed in. But if that is not producing methane in
the reservoir then in will be producing methane elsewhere - cause and effect
is mixed up. Then later on the alternative:

> Groundwater recharge basins are regularly maintained to have less organic
> matter at the bottom, since it can clog the percolation of water into
> groundwater aquifers beneath. In addition, recharge basins are shallower
> than man-made reservoirs and periodically become empty during dry periods
> when less water is available to recharge groundwater.

I'm confused about a shallower basin being less problematic as the methane is
produced by the wet sediment. A shallower basin for the same amount of hydro
power would be much larger.

What is miss is putting the generated methane in relationship with the
generated energy.

~~~
schiffern
To borrow a phrase from Sheldon Brown, "As always, Bill Mollison has the
answer." :)

(for those unfamiliar with what I affectionately call the "Perma-cult":
[https://en.wikipedia.org/wiki/Bill_Mollison](https://en.wikipedia.org/wiki/Bill_Mollison))

> _So, it seems as though hydropower is not as clean as we once thought. But
> that’s isn’t a good reason to be ripping out dams. Hydropower generation
> often replaces much dirtier sources of energy, such as coal and even natural
> gas. In addition, dams provide us a wide range of public benefits such as
> flood control, recreation, and water management._

It sounds like the Permaculture strategy of disfavoring singular large dams
(huge concrete construction projects) and favoring smaller "farm dams" (cheap
earthen construction) is the way to go. The smaller scale means more surface
area:volume, increasing the equilibrium oxygen level in the water and reducing
methanogenesis.

Also, the typical Permaculture dam construction practice is to scrape off and
conserve all the topsoil from the inside of the dam. This should further
reduce methane production (which also represents squandered biomass, ie stored
carbon). This technique is practical on the scale of a farm dam, but totally
impractical for a huge reservoir.

Farm dams have cost advantages in flood control and water management over
monolithic dam projects, since they're near to the big consumers of water
(farms). So the largest diversion canals and tunnels never need to be built.
Simple gravity-fed water run through plastic pipes serves for irrigation
purposes, so it improves on-farm water security.

> _groundwater storage may be a ‘cleaner’ alternative. Groundwater recharge
> basins are regularly maintained to have less organic matter at the bottom,
> since it can clog the percolation of water into groundwater aquifers
> beneath. In addition, recharge basins are shallower than man-made reservoirs
> and periodically become empty during dry periods when less water is
> available to recharge groundwater. This periodic drying out helps keep soils
> aerated, whereas man-made reservoirs can stay inundated with water for
> longer periods of time._

I wonder how "groundwater recharge basins" differ from swales (long on-contour
ditches)? They also intercept large quantities of runoff and divert it to
recharging groundwater. They also require minimal earth movement, since it's a
small surface feature compared to farm dams. Swales can also feed into dams,
dramatically increasing their total catchment _and_ infiltration capacity
(since before the dam overflows, it floods and soaks the length of the swale).

[https://www.youtube.com/watch?v=E79C9tdcgEA](https://www.youtube.com/watch?v=E79C9tdcgEA)

[http://permaculturenews.org/category/earthworks-earth-
resour...](http://permaculturenews.org/category/earthworks-earth-
resources/dams/)

~~~
internaut
Small hydroelectric is extremely efficient.

You can get efficiencies of above 80%. In larger installations 90% or more.
It's expensive but beats the shite out of solar and wind over time. You can
also, if you have an application for physical energy, roughly double the
output.

In addition almost all energy storage capacity for the grid is pumped storage
from hydroelectric stations. I think it is massively overlooked merely because
most people are interesting in scaling and these people overlook the fact that
A: most things do not scale and B: long term maintenance matters. You can run
a hydro plant with next to no maintenance for 100 years. I can't think of
anything close to it and they can easily be fixed or repaired.

It annoys me that micro and small hydro aren't talked about more.

~~~
nkurz
_You can get efficiencies of above 80%. In larger installations 90% or more._

 _You can also, if you have an application for physical energy, roughly double
the output._

Could you explain the apparent contradiction? How are you calculating a 90%
efficiency such that it's possible to get another 90% of "physical" energy?

~~~
internaut
Sure.

With a hydroelectric turbine you can produce electrical power (by black magic
as far as I'm concerned) or mechanical power.

There is a terrific documentary called Ben's Mill on such a mechanical
application here:

[https://www.youtube.com/watch?v=l2KJbRHO76s](https://www.youtube.com/watch?v=l2KJbRHO76s)

That will explain visually how mechanical power can be coached into performing
useful work. It's also worth watching just to see the cows reaction to their
new water vessel at the end, they are like animals out of Disneyland.

Mechanical power when converted to electrical power undergoes a drop in
performance (similar to other power conversions, something is lost).

There is a fascinating article here on the subject, I quote:

"The hydro power installations in use today are actually less efficient than
those of earlier centuries"

"Direct hydropower is at least twice as economically viable as a hydroelectric
operation with the same rate of energy production."

[http://www.lowtechmagazine.com/2013/08/direct-
hydropower.htm...](http://www.lowtechmagazine.com/2013/08/direct-
hydropower.html)

Also take a look at this:

[http://www.lowtechmagazine.com/2013/09/power-from-the-tap-
wa...](http://www.lowtechmagazine.com/2013/09/power-from-the-tap-water-
motors.html)

That is hacking if I ever saw it! I intend to construct a micro hydroelectric
plant myself, so ask away if you've any questions. I love the idea of marrying
up old school technology with modern technology. I also have a terrific idea
for lighting using heliostats, which combines tech literally thousands of
years old with the latest in machine learning.

~~~
msandford
That's not even close to an explanation.

If 1kg of water descends 1m the most power you can hope to extract from that
is U = m x g x h or 1 * 1 * 9.8 ~ 10 J
([https://en.wikipedia.org/wiki/Potential_energy](https://en.wikipedia.org/wiki/Potential_energy))

If you can extract 90% of that, it's 9J. If you can double that efficiency,
it's 18J. Which would make the "over unity" generator folks on YouTube pretty
happy, but the universe generally says you can't really do.

So which is it? Is hydro 90% efficient, or can you get double the power output
if you want mechanical energy? You can't have both.

~~~
internaut
Hmmm. I'm not claiming to defy physics although I see how it came across that
way. That was not my intention.

If you read the literature you can see why I was phrasing it like that so
perhaps I too was misled.

[http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/eng...](http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/eng4431)

The potential energy harvest from a hydro setup must be 90% of available
energy.

In practice half is lost due to the reasons outlined in the low tech magazine
article I linked to. So the electricity production is lower than if we had the
turbine hooked up to a motor. The other possibility is that small scale hydro
is of a lower efficiency and that this explains the paradox. That is: the
literature is talking of a large scale operation that can achieve 90%
efficiency but smaller schemes incur losses that explain why converting a
small hydro setup back to providing mechanical energy can double the output.

~~~
msandford
Assembling and paraphrasing your information:

Turning the shaft horsepower from a hydro turbine into electricity,
transmitting it through wires, transformers, etc, and turning it back into
shaft horsepower through motors, etc is inefficient due to conversion losses.
Just using the shaft horsepower directly incurs none of those conversion
losses. They can be substantial enough in some situations to approach 50%.
This doesn't mean you can harvest more energy than the water can provide, it
means that by eliminating losses you can USE more of the energy that the water
provides, instead of losing it to heat or noise or whatever other conversion
losses.

That's an explanation. What you have linked to and hinted at is only the start
of one.

------
ckastner
According to the report, they supposedly underestimated methane production by
25%.

What surprised me more though was that even going be the previous value (which
I'll simply assume to be 1.5%/1.25=1.2%), that sounds like a _lot_ of
greenhouse gas contribution for a resource which in 2014 "only" contributed
3.8% to global energy consumption, according to [1].

[1]
[https://en.m.wikipedia.org/wiki/World_energy_consumption](https://en.m.wikipedia.org/wiki/World_energy_consumption)

~~~
Shivetya
but energy isn't their main benefit. flood control and proving water to cities
and even farms is the main benefit. throw in the recreational opportunities,
increased tax base because all that lake front is worth something, and it
seems they are more than worth it.

to be honest I walked into that article expecting another dam killer tirade
with an all new reason to take down more and was pleasantly surprised they
defend the use of them in the end

------
teh_klev
Direct link to the study:

[http://bioscience.oxfordjournals.org/content/early/2016/10/0...](http://bioscience.oxfordjournals.org/content/early/2016/10/02/biosci.biw117.full.pdf)

If you see "Failed to load PDF document", clicking "Reload" will load the PDF.

------
Hondor
Methane isn't the most potent greenhouse gas as stated in the article. Water
vapor is both the most potent and the most abundant. It also has a positive
feedback loop so the hotter the Earth gets, the more water vapor goes into the
atmosphere!

~~~
beevai142
A reason to not include water vapor in a list of "greenhouse gases" is its
short lifetime in the atmosphere. If you inject extra water vapor there, it
rains down and exits the atmosphere in a matter of days, whereas methane etc
stay for years --- humans emitting water vapor vs. CO2/etc to the atmosphere
has very different relevance for the physics. Of course, the vapor does have
effect on the radiation physics, and the fact that the equilibrium
concentration depends on temperature leads to the positive feedbacks.

~~~
schiffern
This exactly. What matters is the _equilibrium_ concentration of water vapor.

------
egberts1
I hotly disagree. Reservoir who empty at drought season typically have
immeasurable methane output during good season. -- Lake bed dries up and bakes
in the sun. For that, we can rule out Lake Folsom, California.

------
Angostura
This can be seen as good news, I suspect. Now we have identified a substantial
source of the gasses it gives us an opportunity to look at how we can fix it.
Oygenation? Stirring?

~~~
giarc
Perhaps these shade balls could work. It does mention that they inhibit
microbial growth and slow evaporation.

[http://news.nationalgeographic.com/2015/08/150812-shade-
ball...](http://news.nationalgeographic.com/2015/08/150812-shade-balls-los-
angeles-California-drought-water-environment/)

------
Tharkun
Why does this article talk about cow burps in connection with methane? Surely
that's cow farts? Or do cows somehow produce methane while cud chewing?

~~~
lambertsimnel
I think ruminants including cows do significantly contribute to methane
emissions by burping.

"Cows don't emit 400 quarts of daily flatulence, as the term is usually
understood. According to Professor Johnson, they emit 400 quarts' worth of
burps,known in polite circles as eructation."
[http://www.straightdope.com/columns/read/832/do-cow-and-
term...](http://www.straightdope.com/columns/read/832/do-cow-and-termite-
flatulence-threaten-the-earths-atmosphere)

~~~
ptaipale
And it is fairly self-evident when you think of it: cows are ruminants, and
the process of rumination means fermentation before digestion. Methane is
released in this fermentation, so it naturally comes as burping, not
flatulence.

