> imply opening the gates and releasing all the water
would that be step 1 perhaps?
without much thinking about it, I would expect that the shape of the waterway structure may not really match a natural water course at all. For example, quite a lot of the release mechanisms would be at the top third of the dam wall, etc. Probably very specific to each dam?
That dam also holds back the largest (as far as I recall) pumped hydro storage system in the world. I’m not sure but I think they talk about it in the video you linked if it’s the same one I watched a while back.
The spill way being opened won't release all of the water from a dam. Spill ways are just a type of pressure relief valve to keep the water from destroying the damn. So while it might add more water down stream, it will do nothing for restoring the flooded area upstream of the dam.
First off, that's opening a spillway, and that will still leave a substantial portion of land flooded.
> A dam not holding any water back has far more strength than necessary and will probably last thousands of years.
And, actually isn't true, there's a lot of complicated factors when building a dam, and having a consistent, low lying waterflow (like a river). Depending on the type of damn, soil conditions, etc, it can actually cause disproportionate erosion that will cause the damn to collapse in on itself (occasionally in a surprisingly short time frame, sometimes under a decade even - or in the case of heavy waterflow, hours or days).
So, engineers will sometimes do what you suggested when it's feasible. But, it's not always.
Wouldn't there still be a diversion tunnel or channel from when the dam was originally constructed? I wonder if those could be used to empty a reservoir. Or maybe the water pressure and flow rate of a full reservoir would be too high...
I don't think those are sealed upon completion in a gracefully reversible manner. My guess is dynamite blasting and dumping stone to collapse/fill it in until the water stops flowing.
This short video[0] describes the process used for the Hoover Dam... sSounds like the blasted diversion tunnels were above the river level, then ad-hoc "cofferdams" were filled in both upstream and downstream of the construction site. So even if you reopened the diversion tunnels, it still wouldn't be down to the original level.
It certainly doesn't seem like it'd be a controlled release of the water if you could manage to unseal them. There's no gate...
Exactly right! I was involved in a 'lake tap' project in Oregon where the concrete plug in the diversion tunnel was mechanically demolished down to the minimum safe thickness, then we came in and finished it off with explosives.
A gate structure was first built farther down the tunnel, to allow the operators to again close off the tunnel or chose a given flow level and let me tell you, having to sidle sideways through that partially open gate to go place explosives into the remnants of the tunnel plug was an interesting experience.
All dams have spillways. There are various types and they have several functions: avoiding collapse due to say flooding; allowing controlled release - "spate" - handy for, say, helping salmon to run upstream - yes it is a bit counter-intuitive.
The river Tamar largely delineates Devon and Cornwall in England, UK. It is mostly run off from Dartmoor and hits the sea at Plymouth (which is named after the river Plym). The Tamar is joined by the river Tavy (hence Tavistock, which is a few miles north of Plymouth). The Tamar and Plym run into Plymouth Sound which is the name for the area of sea just south of Plymouth, inside the breakwater. Right, its sodding complicated!
The original dam and reservoir for Plymouth and the surrounding areas was Burrator Reservoir. In the 1980s - Roadford Dam and reservoir was built. I studied Civil Engineering from 1989 to 1991 at Plymouth Polytechnic/Poly South West/Uni of Plymouth - it went through a few changes in a short time!
Roadford has a bellmouth spillway. Basically there is a plughole with a tube to the Tamar in the base of the reservoir with a concrete tower with slits at a set level. Water is heavy stuff and needs to be treated with care so the spill way attempts to dump as much energy as possible, whilst still shifting as much water as possible to down stream.
I left Plymouth in 1996 but I do recall that in 1994 or 5 when there was a dry summer, that a spate was released from Roadford for the salmon. That spate was equivalent to three Burrator reservoirs capacity and it happened over a few days.
What does spillways have to do with this thread of discussion?
They're not generally capable of discharging water down to the original river's level, as they're intended for flood conditions where the reservoir behind the dam is too high. It's the opposite role of what we're talking about.
i.e. not a single spillway here[0] is capable of achieving the equivalent of destroying the dam...
That's a broad statement that doesn't apply as generally as you suggest. For example, low-head dams generally don't have spillways though in essence function as a spillway. They're entirely passive structures with no mechanism for the owner/operator to change the water impoundment or flow rate.
Spillways. I'm not too sure you have any idea about what you are talking about.
Anyway, water at scale is a scary thing. A cubic meter of water is a tonne - 1000 Kg. Look at any river or even a stream and try and mentally construct a cross-section. Say 30m wide and say 3m deep, and assume a 75% section - that's 30x3 = 90x0.75 = 67.5m^2. Let's call it 70m^2.
If the flow in this river is 1 ms-1 then 70 tonnes of water flows per second. That's roughly one and a bit main battle tanks per second!
1 m/s = 2.2 mi/h Let's set walking speed at 3 mph and a river in spate at say 15mph (6.7m/s). Far worse has been seen.
Now you have 70m^2 x 6.7ms-1 = 469 tonnes of water per second. Let's call it 500 tonnes per second.
> You get many of the same environmental benefits (lake area no longer flooded, fish can traverse the base of the dam)
Besides the fact that the lake area will still be partially flooded, as other replies have said, fish are complicated and there are a lot of dam related issues that affect fish passage. Just a few:
- Downstream passage would have to be through spillways. Survival rates are pretty good (95%+) [1], much better than turbine passage, but not as good as not having a dam in the way.
- Conventional spillways open from bottom, which fish have a hard time finding. [2] Granted, if the water levels are reduced this could be less of an issue.
- Time spent in slow moving water increases predation on salmon. [3] If you visit a dam you'll see ospreys all around. Slow water can also favor some species over others.
- There are a bunch of other water quality issues that dams cause, most notably water temperature. The 2002 Klamath fish kill [4] (the largest in history and a major impetus for un-damming the Klamath) was caused by high water temperatures. [5]
- Even shadows can cause significant issues, from structures as small as docks or piers. [6]
- Upstream passage is not solved by opening the spillway and would still be an issue, requiring fish ladders or transportation. All the existing problems with fish ladders apply. [7]
- Besides salmon and trout, other important species get blocked by dams, including sturgeon and lampreys [8], and each are affected by dams in their own way.
At a local dam they recently build a thing they call a "fish ladder" which is a winding stair-like concrete structure that allows fish to migrate up and down the dam.
Perhaps you'd talk about the connection between dams and a climate change movement a little. I'm a little familiar with both and don't see a connection.
Many of these dams are actually causing ecological damage and have also outlived their usefulness and are not sustainable to continue operating and may even cause significant environmental problems if left in place.
Do you know of an example of one of these dams being replaced with coal or gas plants?
> The vast majority of removed dams have been small, either check dams or those used for water diversions, said Warrick. Little dams can be taken down by a small team with a backhoe, Tullos said.
These dams aren't generating any electricity. Try to read the article before taking the headline as an opportunity to get cheap shots on the outgroup.
According to Wikipedia, the Elwha Dam had a hydroelectric capacity of 14.8 MW, which is about five wind turbines. For reference, the US currently has more than 71,000 wind turbines, and on average the US installs 3,000 wind turbines per year, which is 8 per day.
I thought comparing capacity factor instead of capacity would be more fair, but I got roughly the same result. Elwha's capacity factor was, at one point, 39% [0], and capacity factor for wind turbines in the US is ~35% [1]. However, we're still comparing a source of on-demand power to a source of intermittent power.
This is another case where some environmentalists can be more emotional than rational, similar to opposition to nuclear energy.
Dams provided the cleanest, most consistent energy of any source. They also are very effective at energy storage via pumping. We can try to mitigate damage to salmon, but honestly, we're just going to have to let some salmon die to not cook the earth.
I doubt the US will ever be able to build another dam due to NIMBYs and other red tape. So when we get rid of a dam it's gone forever.
America isn't the kind of country that would remove dams for purely environmental reasons.
The fact is, a lot of these dams have long passed their designed lifespan and they're crumbling, a disaster waiting to happen. And though somewhat productive, they're not so productive anyone is about to write a check to cover the maintenance.
In your rush to dunk on your political enemies, you neglected to read the part of the article where it says the vast majority of these dams being removed do not generate any power and were constructed for water diversion or erosion control.
You might want to look at the quantity of power involved before drawing such a conclusion. The article begins with a mention of the dam removal project on the Elwha River: these were the second- and third-smallest hydroelectric plants in the state, generating only 28 megawatts together. In the year that the larger of the two dams was demolished, Washington State installed ten times that capacity in wind power alone. Two thirds of the state's electricity still comes from hydro.
The four dams being removed in the Klamath project offer similarly diminutive capacities: 18, 20, 27, and 98 megawatts respectively. By way of comparison, California is currently installing about 4000 megawatts of solar per year. The dams will not be missed.
Solar and wind are great when it’s sunny or windy. We need dams for green energy the rest of the time.
Comparing max wind capacity to actual outputs from dams is nonsensical. Wind typically produces 30% or less of its max capacity over any period of time and it does so unreliably. The energy from damns is much more valuable.
In addition I see no studies or cited research about how many birds were killed by the increase of wind power, or other environmental impacts that the massive increase in wind turbines may have caused.
You'd have a point if someone were proposing to demolish the Grand Coulee Dam, which generates 6.8 terawatts, or Hoover Dam, which generates a little over 2 terawatts, but that just isn't what's happening here. Removing the Elwha River dams reduced Washington State's hydroelectric capacity by a whopping 0.09%, and removing the four Klamath River dams will reduce California's hydro capacity by 0.76%. These are minor rural dams built a century ago, when the long-distance grid was not what it is today, and they simply do not matter anymore.
1. Your reply to parent said dams’ output is small
2. parent refutes the data
3. You reply again with same message
Can you address the parent’s concern that the data you’re reporting is incorrect? (Solar metrics are based on max / theoretical output and not real output)
Parent did not refute the data, parent said they did not care that a vastly greater quantity of renewables were being installed than the hydro capacity being removed, due to concerns about capacity factor. My second comment therefore showed that the hydro capacity being removed is insignificant relative to hydro alone, without reference to other renewables.
“Comparing max wind capacity to actual outputs from dams is nonsensical. Wind typically produces 30% or less of its max capacity over any period of time and it does so unreliably. The energy from damns is much more valuable.”
Still absolute amount is a factor. A small river dam with 0.09% power can absolutely not be worth it if it is old, in the wrong spot, has huge detrimental effects on downstream areas etc. Everything has to be taken into account.
Sure hydro powers well with wind and solar, but a dam can still be overall a bad thing. And I say this as a guy who grew up next to a dam which is one of 12 dams on that river and I don't have a problem with any single one of them.
Building structures that guide rivers is never a thing where the thing you did decades ago will turn out to be the most clever, most efficient and environmentally best solution. That means people who live with and around rivers have to be able to adapt their plans to what they learned. And sometimes that means realizing a particular dam in a particular place does more harm than good, while this is the polar opposite for some other structure.
The person you quote was mistaken; I cited nameplate capacity, not production output, for both hydro and wind. (My wording could have been clearer.) Furthermore, capacity factors are almost identical: US wind production in 2022 was 35.9% of capacity, while the corresponding figure for hydro was 36.3%.
> Solar and wind are great when it’s sunny or windy. We need dams for green energy the rest of the time.
Dams rely on rainfall and snowmelt to generate power. They are not magically immune from yearly or seasonal variance, and in fact they are quite susceptible to climate change as precipitation patterns shift.
I think energy created through a massive, man-made ecological disaster is not really "clean." Maybe low in carbon, but there's more to the environment than the atmosphere.
I come from an alpine province with 90% water power. Most environmentalists that have criticism of any particular dam are not against dams per se. They might be against a specific dam because it has significant impact on specific areas above or below it.
And those concerns can be very valid. Biodiversity isn't killed in one big action, it is killed by many small ones over centuries. And you can't unkill it easily once it is gone.
I'm finishing up reading Cadillac Desert, a book describing the history of dam building and irrigation project in the US. It goes deep into all aspects of irrigation projects from environmental to economic to political.
Very cool to hear that this dam is getting torn down just 30 years after the book was published.
That book’s a classic for a reason! It’s a fascinating read, whether you’re a water nerd like I am or not - very accessible. I tell people to check it out if they enjoyed Chinatown, since the historical episode it drew inspiration from is so much wilder
It's not even a big loss in clean energy. Oregon solar has been on a roll, their total solar capacity graph[1] shows a very hockey stick-shaped line for the past few years with no sign of letting up. I would wager the state will add more solar generation capacity than it lost from this dam in a matter of months if the trend (the graph ends in 2021) has held up. The eastern half the state is high desert and has plenty of sun.
Just for my own reference, is transferring power from Eastern Oregon to Western Oregon a reasonably efficient thing to do? How much power is lost when we move it across an area the size of Oregon?
"For example, a 100 mi (160 km) span at 765 kV carrying 1000 MW of power can have losses of 0.5% to 1.1%. A 345 kV line carrying the same load across the same distance has losses of 4.2%."
Wikipedia tells me that high voltage lines transmitting 1GW at normal grid voltages will have losses of about 1% over a distance of 100 miles, which is honestly quite a lot. That's 100kW per mile.
Oregon is only a couple hundred miles across, so it's feasible, but with more losses than I thought when I looked it up to answer you.
Isn't the Canadian government currently building and refurbishing some of the largest dams in the world just north of there in British Columbia? I wonder how the impacts compare to the dams being decommissioned in the article.
I only learned about the significance of dam removal when I started fly fishing in WA. This is great news. Very hard to get this kind of unnecessary damage to the ecosystem reversed. The rivers and streams are the vascular system of our environment!
There’s an amazing effort by a nonprofit to sponsor the first Kayak descent of this river by children from indigenous peoples of the region. This is a seriously intense adventure with anticipated class VI rapids.
The Klamath River flows through some amazing areas - starting in the high/dry area east of the Cascades, going through beautiful oak woodlands and then the temperate rainforests on the northern California coast. A really beautiful part of the world.
Orca whales off the coast of Washington (j,k,l pods) are endangered IN NO SMALL PART due to the existence of the Snake River Dam. If the salmon cannot survive then neither can the whales.
73 comments
[ 4.5 ms ] story [ 104 ms ] threadA dam not holding any water back has far more strength than necessary and will probably last thousands of years.
It's obviously far cheaper.
You get many of the same environmental benefits (lake area no longer flooded, fish can traverse the base of the dam).
would that be step 1 perhaps?
without much thinking about it, I would expect that the shape of the waterway structure may not really match a natural water course at all. For example, quite a lot of the release mechanisms would be at the top third of the dam wall, etc. Probably very specific to each dam?
> A dam not holding any water back has far more strength than necessary and will probably last thousands of years.
And, actually isn't true, there's a lot of complicated factors when building a dam, and having a consistent, low lying waterflow (like a river). Depending on the type of damn, soil conditions, etc, it can actually cause disproportionate erosion that will cause the damn to collapse in on itself (occasionally in a surprisingly short time frame, sometimes under a decade even - or in the case of heavy waterflow, hours or days).
So, engineers will sometimes do what you suggested when it's feasible. But, it's not always.
It will deteriorate with age and eventually break in an uncontrolled/unplanned manner anyways.
At least this way you tear it down gracefully with a gradual discharge of the water, and enable restoration of the environment/salmon breeding etc.
This short video[0] describes the process used for the Hoover Dam... sSounds like the blasted diversion tunnels were above the river level, then ad-hoc "cofferdams" were filled in both upstream and downstream of the construction site. So even if you reopened the diversion tunnels, it still wouldn't be down to the original level.
It certainly doesn't seem like it'd be a controlled release of the water if you could manage to unseal them. There's no gate...
[0] https://www.youtube.com/watch?v=n9Gy_1Ppw5U
Exactly right! I was involved in a 'lake tap' project in Oregon where the concrete plug in the diversion tunnel was mechanically demolished down to the minimum safe thickness, then we came in and finished it off with explosives.
A gate structure was first built farther down the tunnel, to allow the operators to again close off the tunnel or chose a given flow level and let me tell you, having to sidle sideways through that partially open gate to go place explosives into the remnants of the tunnel plug was an interesting experience.
Here is a presentation put together on the project: https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2005/tr...
Dude, this has to be one of my favorite and most relevant HN responses ever. Thanks for digging up and sharing that link!
"Water Hammer Equation" "Gate Openings 6'x2' (25% of blast area)" this is bonkers.
And wow, I'd never thought about the effects of a dam on waterway temperature. :-O
The river Tamar largely delineates Devon and Cornwall in England, UK. It is mostly run off from Dartmoor and hits the sea at Plymouth (which is named after the river Plym). The Tamar is joined by the river Tavy (hence Tavistock, which is a few miles north of Plymouth). The Tamar and Plym run into Plymouth Sound which is the name for the area of sea just south of Plymouth, inside the breakwater. Right, its sodding complicated!
The original dam and reservoir for Plymouth and the surrounding areas was Burrator Reservoir. In the 1980s - Roadford Dam and reservoir was built. I studied Civil Engineering from 1989 to 1991 at Plymouth Polytechnic/Poly South West/Uni of Plymouth - it went through a few changes in a short time!
Roadford has a bellmouth spillway. Basically there is a plughole with a tube to the Tamar in the base of the reservoir with a concrete tower with slits at a set level. Water is heavy stuff and needs to be treated with care so the spill way attempts to dump as much energy as possible, whilst still shifting as much water as possible to down stream.
I left Plymouth in 1996 but I do recall that in 1994 or 5 when there was a dry summer, that a spate was released from Roadford for the salmon. That spate was equivalent to three Burrator reservoirs capacity and it happened over a few days.
Oh and Roadford has the river Wolf downstream 8)
They're not generally capable of discharging water down to the original river's level, as they're intended for flood conditions where the reservoir behind the dam is too high. It's the opposite role of what we're talking about.
i.e. not a single spillway here[0] is capable of achieving the equivalent of destroying the dam...
[0] https://en.wikipedia.org/wiki/Spillway
That's a broad statement that doesn't apply as generally as you suggest. For example, low-head dams generally don't have spillways though in essence function as a spillway. They're entirely passive structures with no mechanism for the owner/operator to change the water impoundment or flow rate.
Some dams don't even have gates and are entirely passive structures.
Anyway, water at scale is a scary thing. A cubic meter of water is a tonne - 1000 Kg. Look at any river or even a stream and try and mentally construct a cross-section. Say 30m wide and say 3m deep, and assume a 75% section - that's 30x3 = 90x0.75 = 67.5m^2. Let's call it 70m^2.
If the flow in this river is 1 ms-1 then 70 tonnes of water flows per second. That's roughly one and a bit main battle tanks per second!
1 m/s = 2.2 mi/h Let's set walking speed at 3 mph and a river in spate at say 15mph (6.7m/s). Far worse has been seen.
Now you have 70m^2 x 6.7ms-1 = 469 tonnes of water per second. Let's call it 500 tonnes per second.
Besides the fact that the lake area will still be partially flooded, as other replies have said, fish are complicated and there are a lot of dam related issues that affect fish passage. Just a few:
- Downstream passage would have to be through spillways. Survival rates are pretty good (95%+) [1], much better than turbine passage, but not as good as not having a dam in the way.
- Conventional spillways open from bottom, which fish have a hard time finding. [2] Granted, if the water levels are reduced this could be less of an issue.
- Time spent in slow moving water increases predation on salmon. [3] If you visit a dam you'll see ospreys all around. Slow water can also favor some species over others.
- There are a bunch of other water quality issues that dams cause, most notably water temperature. The 2002 Klamath fish kill [4] (the largest in history and a major impetus for un-damming the Klamath) was caused by high water temperatures. [5]
- Even shadows can cause significant issues, from structures as small as docks or piers. [6]
- Upstream passage is not solved by opening the spillway and would still be an issue, requiring fish ladders or transportation. All the existing problems with fish ladders apply. [7]
- Besides salmon and trout, other important species get blocked by dams, including sturgeon and lampreys [8], and each are affected by dams in their own way.
[1] https://www.salmonrecovery.gov/Hydro/Structuralimprovements/...
[2] https://www.fisheries.noaa.gov/west-coast/endangered-species...
[3] https://www.fisheries.noaa.gov/west-coast/endangered-species...
[4] https://en.wikipedia.org/wiki/2002_Klamath_River_fish_kill
[5] https://www.waterboards.ca.gov/waterrights/water_issues/prog...
[6] https://wdfw.medium.com/casting-shadows-on-the-sound-3a9a555...
[7] https://medium.com/re-form/whats-the-dam-problem-3b5cd839ae7...
[8] https://e360.yale.edu/features/sea-lampreys-pacific-lampreys...
Do you know of an example of one of these dams being replaced with coal or gas plants?
These dams aren't generating any electricity. Try to read the article before taking the headline as an opportunity to get cheap shots on the outgroup.
[0] https://www.osti.gov/servlets/purl/6536093 (page 14)
[1] https://www.eia.gov/todayinenergy/detail.php?id=52038
Dams provided the cleanest, most consistent energy of any source. They also are very effective at energy storage via pumping. We can try to mitigate damage to salmon, but honestly, we're just going to have to let some salmon die to not cook the earth.
I doubt the US will ever be able to build another dam due to NIMBYs and other red tape. So when we get rid of a dam it's gone forever.
The fact is, a lot of these dams have long passed their designed lifespan and they're crumbling, a disaster waiting to happen. And though somewhat productive, they're not so productive anyone is about to write a check to cover the maintenance.
https://www.government-fleet.com/10193319/military-charging-...
The four dams being removed in the Klamath project offer similarly diminutive capacities: 18, 20, 27, and 98 megawatts respectively. By way of comparison, California is currently installing about 4000 megawatts of solar per year. The dams will not be missed.
Comparing max wind capacity to actual outputs from dams is nonsensical. Wind typically produces 30% or less of its max capacity over any period of time and it does so unreliably. The energy from damns is much more valuable.
2. parent refutes the data
3. You reply again with same message
Can you address the parent’s concern that the data you’re reporting is incorrect? (Solar metrics are based on max / theoretical output and not real output)
Sure hydro powers well with wind and solar, but a dam can still be overall a bad thing. And I say this as a guy who grew up next to a dam which is one of 12 dams on that river and I don't have a problem with any single one of them.
Building structures that guide rivers is never a thing where the thing you did decades ago will turn out to be the most clever, most efficient and environmentally best solution. That means people who live with and around rivers have to be able to adapt their plans to what they learned. And sometimes that means realizing a particular dam in a particular place does more harm than good, while this is the polar opposite for some other structure.
Dams rely on rainfall and snowmelt to generate power. They are not magically immune from yearly or seasonal variance, and in fact they are quite susceptible to climate change as precipitation patterns shift.
And those concerns can be very valid. Biodiversity isn't killed in one big action, it is killed by many small ones over centuries. And you can't unkill it easily once it is gone.
Very cool to hear that this dam is getting torn down just 30 years after the book was published.
[1] https://www.oregon.gov/energy/energy-oregon/Pages/Oregon-Sol...
Edit:
Much more information generally: https://en.wikipedia.org/wiki/Electric_power_transmission#Lo...
"For example, a 100 mi (160 km) span at 765 kV carrying 1000 MW of power can have losses of 0.5% to 1.1%. A 345 kV line carrying the same load across the same distance has losses of 4.2%."
Oregon is only a couple hundred miles across, so it's feasible, but with more losses than I thought when I looked it up to answer you.
https://www.riostorivers.org/
Obviously I’m biased to say this as these constructions also prevent me doing my favorite sport in many places