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Shelf life of dams

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Shelf life of dams

Unread postby TheDude » Sun 22 Oct 2006, 17:37:07

How long will man-made dams last without upkeep? How 'bout some examples of the consequences if certain ones gave way?

I grew downstream from Heppner, Oregon, which suffered a terrible flash flood in 1903 which killed about 225 people. In the 80's the Army Corp of Engineers built a roller-compacted concrete dam, which us rubes immediately had our doubts about - should you be able to see the waterline through a dam? Should plants be merrily growing on the dry side of the thing? I heard a story about someone overhearing a ACE employee saying that "We'll get the next one right." An earlier dam in southern Oregon had given out, if I recall correct.
About 12 years ago in a community college's A/V department I noticed a pair of videotapes labeled "Willow Creek Dam." A scientist was wandering around in the galley inside the dam, pulling chunks of concrete out with disturbing ease. My family moved away in the mid-80s but I always wonder if the dam'll hold up.
Last edited by TheDude on Sun 22 Oct 2006, 21:31:50, edited 1 time in total.
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Re: Shelf life of dams

Unread postby green_achers » Sun 22 Oct 2006, 19:24:24

Catastrophic failure like you're talking about is rare, but it happens. When it does, it's a failure of engineering, not "shelf life." No dam AFAIK is designed to fail. What they do is fill with sediment.
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Re: Shelf life of dams

Unread postby Loki » Sun 22 Oct 2006, 19:36:17

Good question, but there isn't a single answer. The Teton Dam in Idaho broke before the reservoir was even filled up, killing 14 people. The Edwards Dam in Maine was almost 130 years old when they removed it for fish habitat restoration--I don't think there was anything wrong with it structurally. I came across a small dam built by the CCC in the 1930s in southern Arizona that was completely silted up, so it was basically useless after a few decades. I've heard Bonneville Dam had a projected 100-year lifespan, but I strongly suspect that was merely for accounting purposes. I wrote the Corps about this but they never responded. The chief engineer for the massive Nagarjunasagar Dam in India claims that it will have "at least" a 1000-year lifespan, which strikes me as more than a bit optimistic.

So the answer is 5 minutes (Teton) to 1000 years (Nagarjunasagar).
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Re: Shelf life of dams

Unread postby gg3 » Mon 23 Oct 2006, 06:21:36

RCC is in my estimation still an experimental technique. It was adopted as a cost-saving measure, as an intermediate grade of construction between earthen dams and poured concrete.

As for the silting problem, couldn't that be controlled by simply dredging the stuff out every so often?
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Re: Shelf life of dams

Unread postby MD » Mon 23 Oct 2006, 06:26:29

TheDude wrote:How 'bout some examples of the consequences if certain ones gave way?



Lake Mead would make a lovely large new canyon should Hoover Dam suddenly give way
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Re: Shelf life of dams

Unread postby Tanada » Mon 23 Oct 2006, 06:43:29

gg3 wrote:As for the silting problem, couldn't that be controlled by simply dredging the stuff out every so often?


More than that, if you are dredging the dam area anyway you can set up a pump dredge and recover all that lovely silt. A portion of the silt can be expelled downstream to keep the channels relatively healthy and the rest can be sold as soil amendment for all sorts of organic farming uses.
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Re: Shelf life of dams

Unread postby green_achers » Wed 25 Oct 2006, 00:46:56

Tanada wrote:
gg3 wrote:As for the silting problem, couldn't that be controlled by simply dredging the stuff out every so often?


More than that, if you are dredging the dam area anyway you can set up a pump dredge and recover all that lovely silt. A portion of the silt can be expelled downstream to keep the channels relatively healthy and the rest can be sold as soil amendment for all sorts of organic farming uses.


Well, then that brings up the design function of the dam. If it's primarily a hydroelectric project, or a "multi-purpose" structure in which a large part of the cost/benefit ratio depends on hydroelectric generation, then the energy cost of dredging has to be taken into account. Something tells me it takes a lot more energy to get silt out of a resevoir than it took to get in.
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Re: Shelf life of dams

Unread postby Tanada » Wed 25 Oct 2006, 06:30:40

green_achers wrote:
Tanada wrote:
gg3 wrote:As for the silting problem, couldn't that be controlled by simply dredging the stuff out every so often?


More than that, if you are dredging the dam area anyway you can set up a pump dredge and recover all that lovely silt. A portion of the silt can be expelled downstream to keep the channels relatively healthy and the rest can be sold as soil amendment for all sorts of organic farming uses.


Well, then that brings up the design function of the dam. If it's primarily a hydroelectric project, or a "multi-purpose" structure in which a large part of the cost/benefit ratio depends on hydroelectric generation, then the energy cost of dredging has to be taken into account. Something tells me it takes a lot more energy to get silt out of a resevoir than it took to get in.


Silt goes in under solar power i.e. rain washes it into the river bed and then downstream. Getting it out mechanically involves physically lifting it from the half mile or so behind the dam up to the lake shore where it can be drained and then shipped out. A simple containment structure/drainage area see CDF1 and CDF2. Warning the first link has a lot of pictures of the many sites in use today in my area.

Obviously it does take energy to lift the dredging's the 1000 feet or so from the water channel bottom into the CDF dike area but if it takes more that 1% of the energy produced by the dam I would be shocked. Basically all you need is a high capacity pump that tolerates muddy water, once the muddy water is in the CDF passive filtering and drainage will put the water back into the lake. If you are slightly smart you build a two cell facility, when the firt cell is full you switch to the second and start hauling the dirt out of the first cell via train or truck for sale as topsoil amendments or fill dirt for construction/land reclimation projects. Worst comes to worst you just ship it down stream and use it to restore natural silt islands below the dam site.

So yes, the silt goes in through natural deposition and doesn't on the face of it cost humans anything so it does cost more to remove the silt than to put it in. In fact you can claim it costs infinitely more even if it costs $1.00 because it didn't cost anything to start with and dividing by zero gives you infinity....
It will cost money to build a CDF for each hydro dam and deal with the silt if the intention is to recover the soil. It would cost much much less to set up a mud pump with the sole purpose of sucking up the mud/silt and expelling it down stream. The dredge in that case simply pulls the mud up and dumps the muddy water into a half pipe feeding down ito the river channel on the downstream side of the dam. No fuss, no muss, you are restoring the natural flow of silt downstream without trying to recover the silt for other uses. You save the cost of all those CDF related operations. The simplest way to do this is to open the dam gates slightly during low demand periods and let natural pressure force the mud through the bypass system. To be effective you would need to do this for say an hour a day every day from midnite to 1 AM, but a lot of ranchers/farmers ect ect depend on the water in the lake and object to their congress persons about such a plan because it 'wastes the water' they want to buy.
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Re: Shelf life of dams

Unread postby Keith_McClary » Tue 12 Jan 2016, 13:04:31

TheDude wrote:How long will man-made dams last without upkeep? How 'bout some examples of the consequences if certain ones gave way?

In the worst-case scenario, according to State Department officials, an estimated 500,000 Iraqis could be killed while more than 1 million could be rendered homeless if the dam, Iraq's largest, collapsed in the spring, when the Tigris River is swollen by rain and melting snow.
...
Mosul Dam, which was built in 1984 by a German and Italian consortium and is 30 miles upstream from Mosul, has long been a maintenance nightmare. Before fighters from the Islamic State, also known as ISIL or ISIS, swept across northern Iraq in 2014, approximately 600 Iraqis worked at the dam.
Because the water was eating away at the gypsum base under the dam, teams of Iraqis drilled holes in that foundation and filled them with a cement grout mixture. That work was carried out three times a day, six days a week.

http://timesofindia.indiatimes.com/worl ... 550225.cms
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Re: Shelf life of dams

Unread postby PrestonSturges » Tue 12 Jan 2016, 17:56:30

At least close to the dam, you could set up a siphon tube suck up the muck as if you were cleaning your aquarium, discharging the water to a settling pond downstream. This would pick up silt and leave gravel.
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Re: Shelf life of dams

Unread postby PrestonSturges » Tue 12 Jan 2016, 18:11:17

Some low head dams last over a century despite being hammered by massive floods. Those are mostly for navigation but some of them also generate hydropower.

The Conawingo Dam on the Susquehanna River has been around since 1928. I has never been overtopped, but Hurricane Agnes came very very close.

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Re: Shelf life of dams

Unread postby Lore » Tue 12 Jan 2016, 18:25:34

Here I looked it up for you.

Shelf life is generally 7-10 days, but can be longer for hard shell clams and oysters. Because soft shelled clams cannot close their shells they can have a shorter shelf life than hard shell clams and oysters. Keep shellfish alive until ready to prepare.
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Re: Shelf life of dams

Unread postby hvacman » Tue 12 Jan 2016, 19:58:39

Whats the shelf life of THIS dam?

https://en.wikipedia.org/wiki/Shasta_Dam

Shasta dam - my backyard hydro system:) 602 feet tall, 543 feet thick of solid reinforced concrete at the base. 30 feet wide at the top. 15 million tons of concrete. I don't think a Lancaster could do much to the basic structure - maybe just take out the hydro plant or the drum gate at the top.
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