[xyzdonna]

Donna, finally words coming out of you that make sense! There is hope for you after all, I am impressed!
All but the nukes will produce co2.. Another co2 free (kinds of) is hydroelectric, you know, like all those dams the eco-nuts want to blow up in the North West?

I also have trouble with tv sound. When I can hear, everyone else has to move over two counties. The solution, if you can find it is simple. An fm transmitter and wireless earphones, as for ipod. Cheap, battery powered and mobile.

Hi jhowelb,
Finally words coming out of you too jhowelb. For a while there we didn't hear anything at all from you. I've been worried about you, feeling any better? That flu bug is bad news, I hope you remember to get your flu shot next year.
I believe in dams. We have Chickamauga dam right here in Chattanooga that provides a lot of our power. We've had low cost electricity for decades here in the Chattanooga area. I don't see why the "eco-nuts" would be against dams, they are a solar powered renewable resource. The Chickamauga dam also protects us from the devastating floods that used to frequent the Tennessee valley. Get well soon jhowelb, and get plenty of bed rest. I hope you are getting better.
Take care,
xyzdonna
PS: Spouse tried 3 different wireless headphones. They averaged about a 3 day lifespan before they went kaput. We had to take them all back. Cordless phones last for a year or two. Why can't they make wireless headphones that last that long? What brand are you using? Thanks, xyzdonna

[Geof]

....I don't see why the "eco-nuts" would be against dams, they are a solar powered renewable resource.....

It depends on your time frame, and on the river. Most dams will eventually silt up and be worthless both for power generation and flood control. Eventually, in this context, being anywhere from fifty to a couple of hundred years.

[dynosor]

I don't see why the "eco-nuts" would be against dams, they are a solar powered renewable resource.

Hydro-electric turbines kill fish: http://eesc.oregonstate.edu/salmon/human/dams.html

I guess regular dams frustrate fish swimming up river. Do beavers and fish ever get along?

[xyzdonna]

http://www.collectionsetc.com/Item75044.aspx#

Hi jhowelb,
Isn't that amazing, you answered my question two hours before I asked it! Look at the times on the post, two hours to the minute! You posted your answer to my queation at 5:39 and I asked the question at 7:39. No, wait, there's a 3 hour time difference between California and Chattanooga. You are sneaky jhowelb, you had an extra hour to answer my question due to the time differential.
I figured it out. Hmmm, I think I figured it out, but your post preceded mine. I'll have to think some more.
Take care and get well,
xyzdonna

[fizzissist]

It depends on your time frame, and on the river. Most dams will eventually silt up and be worthless both for power generation and flood control. Eventually, in this context, being anywhere from fifty to a couple of hundred years.

Another problem with dams is they're an amazing methane generator...something the eco's don't ever address. Google'ing '3 Gorges Methane' uproots some interesting views.

[xyzdonna]

It depends on your time frame, and on the river. Most dams will eventually silt up and be worthless both for power generation and flood control. Eventually, in this context, being anywhere from fifty to a couple of hundred years.

Hi Geof,
Well the Chickamauga Dam was completed in 1940. So it's going on 67 years now. I think the key is maintenance. The Tennessee Valley Authority (a US government agency) has been diligent in maintaining the dam. They recently overhauled the locks. Chickamauga dam is good for 128 Megawatts.
Here are some pix of the dam: http://www.janandpat.net/dams/tva/chickamauga.htm
Take care,
xyzdonna

[Geof]

...I think the key is maintenance. The Tennessee Valley Authority (a US government agency) has been diligent in maintaining the dam....

Not really. The structure of the dam may be good for thousands of years, the problem is eventually it fills with silt so there is no room for water.

Have you read about the recent release from Glen Canyon into the Colorado in an effort to replenish sandbars in the canyon. All the sand and silt that used to get carried down the Colorado before the dam is now trapped behind the dam. If the sluice gates are opened wide a minuscule fraction gets flushed out with the flow. However, the stuff that is trapped will eventually fill the lake until it is no longer possible to run the level down prior to spring snow melt to provide a cushion for flood flow. It will also make it no longer possible to store water for later release for hydro power and irrigation.

This applies to practically all dams.

[martinw]

Another problem with dams is they're an amazing methane generator...something the eco's don't ever address. Google'ing '3 Gorges Methane' uproots some interesting views.

Dear fizzissist,

I was at a very small school in England between the age of seven and thirteen. The swimming pool comprised a dammed section of a tiny river, with a concrete base and a sluice at both ends.

Every spring, the pool was by-passed, and thirty tiny boys were put into THE POND PARTY. We just heaved the mud from the last year's sedimentation into the by-pass to empty it. As you may imagine, we just loved it. Probably, today, the headmaster would be put in jail, on a raft of Safety legislation offences...

Yes, you are right about methane generation. Before the pond was drained, we would get a jam jar, hold it upright full of water below the pond surface, and jab a stick into the bottom of the pool to liberate the methane bubbles.

The jars were then lit with a satisfying pop with strictly forbidden matches.

I guess that it is not beyond the wit of modern technology to mount another POND PARTY....?

Best wishes,
Martin

[fizzissist]

It is estimated that globally 1%/yr water storage capacity is lost to silting.

[jhowelb]

Hi jhowelb,
Isn't that amazing, you answered my question two hours before I asked it! Look at the times on the post, two hours to the minute! You posted your answer to my queation at 5:39 and I asked the question at 7:39. No, wait, there's a 3 hour time difference between California and Chattanooga. You are sneaky jhowelb, you had an extra hour to answer my question due to the time differential.
I figured it out. Hmmm, I think I figured it out, but your post preceded mine. I'll have to think some more.
Take care and get well,
xyzdonna

Temp just jumped to 102* again. Posts may be limited in number.

[fizzissist]

.......Before the pond was drained, we would get a jam jar, hold it upright full of water below the pond surface, and jab a stick into the bottom of the pool to liberate the methane bubbles.

The jars were then lit with a satisfying pop with strictly forbidden matches.

I guess that it is not beyond the wit of modern technology to mount another POND PARTY....?

1.3Billion Chinese, jam jars, and matches all at once in 3 Gorges will probably knock earth out of it's orbit.

[martinw]

1.3Billion Chinese, jam jars, and matches all at once in 3 Gorges will probably knock earth out of it's orbit.

Dear fizzissist,

If thirty undernourished 7 to 13 year-olds could keep their pond in order on an annual basis, I am confident that the vast population of China can do the same. Besides, we only had shovels. They have more technology at their disposal than we had...

Best wishes,
Martin

[xyzdonna]

Not really. The structure of the dam may be good for thousands of years, the problem is eventually it fills with silt so there is no room for water.

Have you read about the recent release from Glen Canyon into the Colorado in an effort to replenish sandbars in the canyon. All the sand and silt that used to get carried down the Colorado before the dam is now trapped behind the dam. If the sluice gates are opened wide a minuscule fraction gets flushed out with the flow. However, the stuff that is trapped will eventually fill the lake until it is no longer possible to run the level down prior to spring snow melt to provide a cushion for flood flow. It will also make it no longer possible to store water for later release for hydro power and irrigation.

This applies to practically all dams.

Hi Geof,
Again you've taught me something I didn't know. Remember when you taught me that CO2 was created when they made concrete? Well I'm learning thanks to you. But couldn't they just dredge the silt out? That would seem like the easy fix.
Take care,
xyzdonna

[Geof]

..... But couldn't they just dredge the silt out? That would seem like the easy fix.
Take care,
xyzdonna

The quantities are mind boggling, it simply is not possible even with small dams. Also it would probably use as much energy as the dam is converting to electricity.

[ImanCarrot]

Hmm.. why didn't they lay pipes parallell to the damn (on the water side) with high pressure air (punch holes in the pipe) to keep the silt agitated- it'd surely flow though the sluice gates if agitated and in suspension? Just a thought.

I know a guy who designs damns for all over the world. If I see him at the weekend I'll ask him why this wouldn't work... there has to be a reason otherwise it'd have been tried surely?

[Geof]

Hmm.. why didn't they lay pipes parallell to the damn (on the water side) with high pressure air (punch holes in the pipe) to keep the silt agitated- it'd surely flow though the sluice gates if agitated and in suspension? Just a thought...

Exact opposite happens if you aerate the water with a bubbler. The bubbles make the water column less dense and the silt settles faster.

Actually I should say fine sand not silt, colloidial size particles stay in suspension but bigger ones do settle.

[fizzissist]

The bubbles make the water column less dense and the silt settles faster.

Think fluidized bed. (they're really fun to play with!) I built one with 3 powerful vacuum motors and a large column of sand for a lab. One interesting facit was the level of sand when you filled it normally, then when you shut it down after fluidization the settled level would often be lower.

I wonder if you could allocate some nominal % of the dam's electrical output to a giant silt-removing Roomba?
(I just invented that, so don't you guys be gettin' any ideas!!)

[martinw]

Another problem with dams is they're an amazing methane generator...something the eco's don't ever address. .

Dear fizzissist,

This methane thing puzzles me.

My understanding is that methane is produced when vegetable matter rots in anaerobic conditions. I can see that a project like the Three Gorges Dam will result in large areas of vegetable stuff being covered in water...hence the dam will become a net methane producer initially. I suppose that one could argue that it will continue to be a methane producer because there is a larger area of water into which trees and other plants might fall.

Now consider the area of all the lakes in Canada, or the area of water in the Amazon rainforest, the Russian taiga etc etc. There must be shed-loads of dead plants swilling thereabouts, all happily giving off clouds of gas, as they have done for millions of years.

Surely the methane contribution of a few large dams is absolutely miniscule in comparison?


Best wishes,

Martin

PS:Actually, does rotting vegetation in salt water produce methane?

[fizzissist]

There were studies done back in the late '70s by Hanson, Harrits, Brock, and Fallon that focused on Canadian lakes and methane/methane oxidation.

They found that methane was very lake specific, depending on depth, temperatures, the nature of the water input, etc., etc. The more oxygenated the water, the less methane. On top of that, it was seasonal.

[Geof]

.......
Surely the methane contribution of a few large dams is absolutely miniscule in comparison?


Best wishes,

Martin

PS:Actually, does rotting vegetation in salt water produce methane?

The Canadian and Russian stuff is cold so it is not decomposing as fast as it is being laid down. This is the source of the peat bogs and frozen tundra; which if they do warm up enough will start to decompose and release either methane or CO2 depending largely on whether they stay flooded.

The Amazon forests are different because they are warm. In these regions there is little accummulation of non-decayed vegetation in the type of conditions that cause anaerobic decomposition.

Yes rotting vegetation, phyto-plankton, in sea water does produce methane. This normally occurs in the deep ocean where it is anoxic and cold and it is believed to be the source of the methane hydrates in the ocean floor.