Large Scottish Pumped Storage Hydroelectric Reservoir and Dam (@ Coire Glas)

[Peter Dow]

I am presenting here my vision for a large pumped storage hydroelectric 2-square kilometres surface-area reservoir and 300+ metre tall dam which I have designed for the Coire Glas site, Scotland.

 

(View site using Google Earth where the convenient label is "Loch a' Choire Ghlais" - or, http://tinyurl.com/coireglas)

 

I was inspired to conceive and to publish my vision by learning of the Scottish and Southern Energy (SSE) proposal to build a smaller hydroelectric pumped-storage scheme at Coire Glas which has been presented to the Scottish government for public consultation.

 

I have not long been aware of the SSE plan for the Coire Glas scheme, not being a follower of such matters routinely, but I was prompted by an earlier tangentially-related news story (about energy storage technology for renewable energy generators such as wind farms) to write to Members of the Scottish Parliament on the merits and urgency of new pumped storage hydroelectric power for Scotland on 14th February and a reply from Ian Anderson, the parliamentary manager for Dave Thomson MSP received the next day, the 15th February informed me about the SSE plan and Ian added "initially scoped at 600MW but, to quote SSE, could be bigger!"

 

I replied to Ian "So the schemes proposed by the SSE are welcome and ought to be green-lighted and fast-tracked, but I am really proposing that Scots start thinking long term about an order of magnitude and more greater investment in pumped storage hydroelectric capacity than those SSE plans."

 

So I had in mind "bigger would be better" but it was not until the next day on the 16th February when a news story informed me that the SSE plans had been submitted to the Scottish government for public consultation that I thought "this needs consideration now".

 

So starting late on the night of the 17th, early 18th February and all through the weekend, I got busy, outlining my alternative vision for a far bigger dam and reservoir at the same location.

 

So this is my vision as inspired by the SSE plan. If my vision is flawed then the fault is mine alone. If my vision is brilliant, then the brilliance too is mine.

 

Image also hosted on postimage

 

The black contour line at 550 metres elevation shows the outline of the SSE proposed reservoir of about 1 square kilometre surface-area and the grey thick line shows the position of the proposed SSE dam which would stand 92 metres tall and would be the tallest dam in Scotland and indeed Britain to date though it seems our dams are several times smaller than the tallest dams elsewhere in the world these days.

 

Part of the red contour line at 775 metres elevation, where the red line surrounds a blue shaded area, blue representing water, shows the outline of my larger reservoir of about 2 square kilometres surface-area and the thicker brown line shows the position of my proposed dam which would stand 317 metres tall which would be one of the tallest man-made dams in the world.

 

Excavated Reservoir Bed

 

The green ellipse of major diameter of 1.5 kilometres and minor diameter of 1 kilometre represents an excavated reservoir bed, as flat and as horizontal as practical, at an elevation of 463 metres.

 

Since an excavated reservoir bed is not, that I can see, part of the SSE plan, at any size, I will provide some more information about my vision for that now.

 

The basic idea of excavating a flat or flattish reservoir bed is to increase the volume of the water stored in the reservoir because more water means more energy can be stored.

 

Depending on the geology and strength of the rock of Coire Glas the walls of the reservoir bed perimeter could be as steep as vertical from the reservoir bed up to the natural elevation of the existing rock surface which would mean, presumably, blasting out rock to create a cliff which at places could be as much as about 290 metres tall.

 

Near the dam, the reservoir bed perimeter wall would be only 40 metres or less tall. The further from the dam, the higher the wall will be and the more rock needs to be excavated.

 

A vertical reservoir bed perimeter wall would be ideal to maximise reservoir volume wherever the geology provides a strong stone which can maintain a vertical wall face without collapse, (a stone such as granite perhaps).

 

Where the geology only provides a weaker stone then a sloping perimeter wall at a suitable angle of repose for reliable stability would be constructed.

 

So the reservoir perimeter wall could be as sloped as shallow as 45 degrees from the natural elevation at the perimeter of the eclipse sloping down to the reservoir bed at 463 metres elevation in the case of the weakest and most prone to collapse kinds of stone.

 

Exactly how strong the stone is at each location I guess we'll only find out absolutely for sure if and when engineers start blasting it and testing the revealed rock wall face for strength.

 

The shape of the perimeter of the excavated reservoir bed is not absolutely critical. So long as it ends up as a stable wall or slope, however it is shaped by the blasting, it will be fine. There is no need to have stone masons chip the perimeter smooth and flat! The ellipse is simply the easiest approximate mathematical shape to describe and to draw. If the end result is not a perfect ellipse, don't worry, it will be fine!

 

OK, well I guess that's the vision part over. The rest is fairly straight-forward engineering I hope. Oh, and there is always getting the permission and the funding to build it of course which is never easy for anything this big.

 

OK, well if anyone has any questions or points to make about my vision or can say why they think the SSE plan is better than mine, or if you don't see why we need any pumped storage hydroelectric scheme at Coire Glas, whatever your point of view, if you have something to add in reply, please do.

Edited February 20, 2012 by Peter Dow

[CaptainPanic]

Let me start with a compliment and an expression of happiness, before going into my comments (comments always sound so negative). It's a good post... and I am really happy that the Scots are building an energy storage. Hopefully this will shut up the critics who say you cannot store wind energy. It's always been possible... but for some reason the anti-wind lobby has always managed to direct the attention to crappy hydrogen storage or batteries, and just omitted cost-effective hydro-electric storage from the analysis. I'm happy to see this on the forum

 

Comments:

 

What matters mostly is the difference in height between the stored water and the bottom reservoir (Loch Lochy). So, in a nutshell, a cubic meter of water stored at the max. height can store more energy than a cubic meter at the bottom... and you can express that in euros or pounds.

But to store it at a higher altitude, you need a bigger dam. The question is: is it worth the extra investment to store those extra cubic meters?

 

And in addition, in your case, it is worth the money to dig a pit in the middle of the lake to store more water at lower elevation? I am just guessing that it is simply too costly to excavate a big hole to store more water, because the excavation itself costs money, but it will also (slightly) increase the cost of the dam itself. And that's for some cubic meters of water that you should only need when the dam is nearly empty.

 

A risk analysis should show how often a long period without any wind occurs, when you would need every cubic meter of water to compensate the lack of wind (the dam stores wind energy after all). Also for this reason, it might not be necessary to dig a big hole in the ground.

 

So, in short, the costs of the water stored should be competitive in terms of money per energy stored. And the size of the lake should be proportional to the amount of energy you expect to store, based on the capacity of the wind farms, the general weather patterns, and the risk you're willing to take that the weather is temporarily very un-Scottish.

 

There is no doubt that you can store far more energy in the plan you present. The big question is: is there any use for such a large dam?

 

[edited: fixing typos and adding another comment]

Edited February 21, 2012 by CaptainPanic

[Peter Dow]

Let me start with a compliment and an expression of happiness, before going into my comments (comments always sound so negative). It's a good post... and I am really happy that the Scots are building an energy storage. Hopefully this will shut up the critics who say you cannot store wind energy. It's always been possible... but for some reason the anti-wind lobby has always managed to direct the attention to crappy hydrogen storage or batteries, and just omitted cost-effective hydro-electric storage from the analysis. I'm happy to see this on the forum

Thank you.

 

Comments:

 

What matters mostly is the difference in height between the stored water and the bottom reservoir (Loch Lochy). So, in a nutshell, a cubic meter of water stored at the max. height can store more energy than a cubic meter at the bottom... and you can express that in euros or pounds.

But to store it at a higher altitude, you need a bigger dam. The question is: is it worth the extra investment to store those extra cubic meters?

Yes it is worth it.

 

And in addition, in your case, it is worth the money to dig a pit in the middle of the lake to store more water at lower elevation? I am just guessing that it is simply too costly to excavate a big hole to store more water, because the excavation itself costs money, but it will also (slightly) increase the cost of the dam itself. And that's for some cubic meters of water that you should only need when the dam is nearly empty.

Yes excavating the reservoir bed is worth it.

 

A risk analysis should show how often a long period without any wind occurs, when you would need every cubic meter of water to compensate the lack of wind (the dam stores wind energy after all).

Also for this reason, it might not be necessary to dig a big hole in the ground.

All the additional energy storage capacity created by excavating the reservoir bed will be utilised and indeed much more storage capacity will be needed requiring additional reservoirs and dams.

 

So, in short, the costs of the water stored should be competitive in terms of money per energy stored. And the size of the lake should be proportional to the amount of energy you expect to store, based on the capacity of the wind farms, the general weather patterns, and the risk you're willing to take that the weather is temporarily very un-Scottish.

 

There is no doubt that you can store far more energy in the plan you present. The big question is: is there any use for such a large dam?

The simple answer is "yes".

 

The smaller dam proposed by the SSE only stores about 30 Gigawatt hours and they will only be able to supply say their planned 0.6 Gigawatts for 50 hours before the dam empties. Now 0.6 gigawatts is not to be sneezed at but it is insufficient by a long way to supply all the power needs.

 

If you want some figures then here are some for Britain as a whole which has an integrated electricity supply grid.

 

Wikipedia: National Grid (Great Britain)

 

Maximum demand (2005/6): 63 GW (approx.) (81.39% of capacity)

Annual electrical energy used in the UK is around 360 TWh (1.3 EJ)

 

There is an average power flow of about 11 GW from the north of the UK, particularly from Scotland and northern England, to the south of the UK across the grid. This flow is anticipated to grow to about 12 GW by 2014.

 

So it is clear that 30 giga-watt-hours could supply British 63 giga-watts for about half an hour.

 

Now if my proposed far larger dam stored 6 times the energy (twice the area and 3 times the depth of water equals 6 times the volume of water) that would still only be 3 hours supply at 63 gigawatts and the wind is becalmed for far longer than that.

 

So there is no risk that this will be too big. There is a certainty that it will not be enough but it is a start.

 

The reason for building bigger while we are at it is to make an efficient use of the site because there will be a limited number of suitable sites and if the site is used up with a smaller dam then that is a possible opportunity to increase capacity lost.

 

Image also hosted on postimage

Edited February 21, 2012 by Peter Dow

[CaptainPanic]

So it is clear that 30 giga-watt-hours could supply British 63 giga-watts for about half an hour.

That's a little too simplistic for my taste...

 

You only need to store the energy from non-continuous sources of electricity, like wind and solar. Since we can say that solar is negligible, you should look at wind only.

 

Also, by managing the grid efficiently, some fluctuations in wind power can be absorbed without such an energy storage.

 

So, looking at the total wind power in the UK (6 GW at peak performance), you can make an estimate of what the capacity of 30 GWh means. It means you can store a good 5 hours of all the UK's wind power at peak performance...

 

But since the grid can compensate for fluctuations too, and there may be other storages too, your grid can go without any wind for quite a significant time. Perhaps a day or so. And that's the goal: to compensate for relatively short term fluctuations.

 

Your bigger dam can store 6 times as much: 30 hours of all the UK's wind energy at peak performance. And given that the grid can absorb fluctuations, and that there may be other storages too, with such a giant dam, the grid can go without any wind for perhaps up to a week... But when does that happen in the UK, especially not in Scotland??

 

Maybe the time frames (a day vs. a week) are off. But this is the type of argument that matters, imho.

 

There is less interest to store any other energy (coal power can switch up or down within the hour, gas power plants in a matter of minutes or seconds)... so I have left that out of the equation.

Edited February 21, 2012 by CaptainPanic

[michel123456]

If I understand well (please correct me) the main goal is to produce electricity as a backup when wind is unavailable (or too intense). Water does not come naturally into the lake, it would have to be pumped (using electricity from wind).

The calculated capacity should be of about 24h of backup for the initial SSE project.

 

There are already negative reactions to the SSE dam.

 

Your dam looks out of size.

It will be one of the highest dam in the world. The dimension of the artificial lake are far too small for a so big project.

You should make an elevation drawing of your dam.

It would look like this:

1km wide, 300m high (the Eiffel tower).

That looks too much to me.

[Peter Dow]

That's a little too simplistic for my taste...

 

You only need to store the energy from non-continuous sources of electricity, like wind and solar. Since we can say that solar is negligible, you should look at wind only.

Sure wind power is the favourite for planned future investment in renewable energy generating capacity.

 

Wikipedia: Wind power in the United Kingdom

 

RenewableUK estimates that this will require 3540% of the UKs electricity to be generated from renewable sources by that date,[11] to be met largely by 3335 GW of installed wind capacity.

 

Also, by managing the grid efficiently, some fluctuations in wind power can be absorbed without such an energy storage.

You mean when the wind isn't blowing in the south / north but it is blowing in the north / south then the grid can distribute power to where it is to where it is needed?

 

Sure that goes without saying but there are going to be many days when the wind isn't blowing appreciably anywhere on mainland Britain and that's when you need to have stored energy available, or else you'll be forced to fire up your back-ups, gas / coal / nuclear / whatever.

 

So, looking at the total wind power in the UK (6 GW at peak performance),

 

Oh, we've used the same reference. That'll cut down on the arguments then.

 

you can make an estimate of what the capacity of 30 GWh means. It means you can store a good 5 hours of all the UK's wind power at peak performance...

And when future installed wind power capacity goes up to 33-35 GigaWatts then the SSE plan will last less than one hour before you are reaching for the start up button for the back-ups.

 

But since the grid can compensate for fluctuations too, and there may be other storages too, your grid can go without any wind for quite a significant time. Perhaps a day or so. And that's the goal: to compensate for relatively short term fluctuations.

Sure if we want to burn fossil fuels or use nuclear then we can but we don't want to - we want to use renewable sources only.

 

Your bigger dam can store 6 times as much: 30 hours of all the UK's wind energy at peak performance. And given that the grid can absorb fluctuations, and that there may be other storages too, with such a giant dam, the grid can go without any wind for perhaps up to a week... But when does that happen in the UK, especially not in Scotland??

Well right now, my 6 times the SSE's 30 GWhrs would be 180 Gigawatt-hours which would last a respectable 180 / 6 = 30 hours compensating for all current wind capacity when becalmed but as wind generating capacity rises to 33-35 GWhrs then we are back to 180 / 34 = 5.5 hours, useful but by no means enough for weather patterns that tend to stick around for days at a time.

 

Maybe the time frames (a day vs. a week) are off. But this is the type of argument that matters, imho.

 

There is less interest to store any other energy (coal power can switch up or down within the hour, gas power plants in a matter of minutes or seconds)... so I have left that out of the equation.

 

OK I think you are concentrating on the current needs for storage but you need to look to the future of wind power. Perhaps if I may quote a recent email I wrote explaining the strategic needs in the future.

 

Scotland best for pumped-storage hydroelectricity energy economy

 

This is a statement of the obvious as far as Scottish electrical power-generation engineers and scientists are concerned I expect but I am making this statement anyway, not for the benefit of our scientists or engineers but to inform the political debate about the potential of the Scottish economy "after the North Sea oil runs out" because political debate involves mostly non-scientists and non-engineers who need to have such things explained to them.

 

The Scottish economy has a profitable living to make in future in the business of electrical energy import/export from/to English electrical power suppliers and perhaps even to countries further away one day.

 

The tried and tested engineering technology we Scots can use in future to make money is pumped-storage hydroelectricity.

 

 

Wikipedia: Pumped-storage hydroelectricity

 

"The technique is currently the most cost-effective means of storing large amounts of electrical energy on an operating basis, but capital costs and the presence of appropriate geography are critical decision factors."

 

In Scotland, the Cruachan Dam pumped-storage hydroelectric power station was first operational in 1966 and was built there to take advantage of Scotland's appropriate geography and available capital.

 

So Scotland has the appropriate geography for pumped-storage hydroelectric power and we have the capital particularly if we invest some of the taxes on North Sea oil before it all runs out and it is all spent.

 

Investment in wind-power energy generation is proceeding apace, in Scotland, in England, on and offshore, and that's very "green" and quite clever, though wind power is not as dependable as tidal power, but unless and until sufficient capacity to store energy becomes available to supply needs when the wind isn't blowing then conventional, and perhaps increasingly expensive, coal, gas or oil burning or nuclear energy power will still be needed to keep the lights on when the wind doesn't blow.

 

Scottish opportunity

 

Here is the opportunity for the Scottish economy in a future where wind-power generation is increasingly rampant: if we Scots build a large capacity of new pumped-storage hydroelectric power stations, not only can we supply all our own Scottish energy needs from "green" renewable energy schemes, but we could provide energy storage capacity for customers outside Scotland, particularly in England, who live in a land not so well endowed with appropriate geography for hydroelectric power.

 

 

In future, a Scotland with investment in a massive pumped-storage hydroelectric capacity could buy cheap English wind-power while the wind is blowing then sell the same energy back to English power suppliers, at a profit, when the wind isn't blowing and the English will pay more for energy.

 

So everyone wins, the energy is all green, the electricity supply is always available when it is needed and that is how the Scottish energy economy does very well after the North Sea oil runs out.

 

So problem solved but not job done as yet. We Scots do actually need to get busy investing and building pumped-storage hydroelectric power generation and supply capacity in Scotland now.

Edited February 21, 2012 by Peter Dow

[Peter Dow]

If I understand well (please correct me) the main goal is to produce electricity as a backup when wind is unavailable (or too intense).

Unavailable, yes, (too intense, no comment).

 

Water does not come naturally into the lake, it would have to be pumped (using electricity from wind).

That's the general idea.

 

The calculated capacity should be of about 24h of backup for the initial SSE project.

SSE say about 30 giga-Watt-hours of energy stored and they intend a 0.6 giga-Watts generator, and 30 / 0.6 = 50 hours, so twice your "24h" comfortably.

 

My point is that 0.6 gW is much less than the currently installed wind-power in Britain which is about 6gW.

 

There is a need for more power and therefore a bigger reservoir than the SSE plan now and even more so in future.

 

There are already negative reactions to the SSE dam.

Someone is always going to have a negative reaction. Name me one project ever that someone didn't have a negative reaction to.

 

Your dam looks out of size.

Define "out of size". It is as big as it needs to be.

 

It will be one of the highest dam in the world.

Yes I did mention that in my original post.

 

The dimension of the artificial lake are far too small for a so big project.

 

I am working with the dimensions of the site which the SSE plan to use. I don't have a free choice of sites or land which I can flood. If I propose to flood land other than than the land the SSE plan to flood this is will not even be considered seriously coming from an independent author like myself.

 

You should make an elevation drawing of your dam.

It would look like this:

1km wide, 300m high (the Eiffel tower).

That looks too much to me.

That is an excellent idea. Thank you.

 

Cross section of the Dow-dam reservoir

 

 

Cross section along the major diameter of the elliptical excavation of the reservoir bed

 

Also hosted on PostImage.org

Edited February 21, 2012 by Peter Dow

[CaptainPanic]

And when future installed wind power capacity goes up to 33-35 GigaWatts then the SSE plan will last less than one hour before you are reaching for the start up button for the back-ups.

 

[...]

 

OK I think you are concentrating on the current needs for storage but you need to look to the future of wind power. Perhaps if I may quote a recent email I wrote explaining the strategic needs in the future.

Yep. This is the core of what we disagree about.

It's pretty hard to make an investment which you will only need in a decade from now.

 

I would advise all countries to consider the issue of energy storage though, and to scout for other locations for similar plans. The future will come eventually, so we will need additional storage.

 

I just don't think that the 1st purpose-built energy storage lake in Scotland should immediately solve all future problems. Take it one step at a time. Surely there is some other glen, valley or lake in Scotland which you can use too?

[michel123456]

Cross section of the Dow-dam reservoir

 

I ment an elevation (or longitudinal section) of the dam.

 

It has to be expected that your dam will have a vertical surface of about 5 times that of the original project. If you expect twice the thickness (very conservative approach) your dam will be 10 times that of SSE.

 

Also you must take into account that the water used to refill the damp must come from somewhere in the surroundings.

Have a look at the Grande Dixence dam in Switzerland, it is smaller than yours.

 

The Grande Dixence Dam is a 285 m (935 ft) high, 700 m (2,297 ft) long concrete gravity dam. The dam is 200 m (656 ft) wide at its base and 15 m (49 ft) wide at its crest. The dam's crest reaches an altitude of 2,365 m (7,759 ft). The dam structure contains approximately 6,000,000 m3 (211,888,000 cu ft) of concrete.[1] To secure the dam to the surrounding foundation, a grout curtain surrounds the dam, reaching a depth of 200 m (656 ft) and extending 100 m (328 ft) on each side of the valley.[3]

 

Although the dam is situated on the relatively small Dixence River, water supplied from other rivers and streams is pumped by the Z’Mutt, Stafel, Ferpècle and Arolla pumping stations. The pumping stations transport the water through 100 km (62 mi) of tunnels into its reservoir, Lac des Dix. Water from the 87 m (285 ft) high Cleuson Dam, located 7 km (4 mi) to the northwest, is also transported from its reservoir, the Lac de Cleuson. Three penstocks transport water from Lac des Dix to the Chandoline, Fionnay, Nendaz and Bieudron power stations, before being discharged into the Rhône River below.[4] All the pumping stations, power stations and dams form the Cleuson-Dixence Complex. Although the complex operates with water being pumped from one reservoir to another, it does not technically qualify as a pumped-storage scheme. [5]

 

Most of the water comes from glaciers when they melt during the summer. The lake is usually at full capacity by late September, and empties during the winter, eventually reaching its lowest point around April.

 

Also i suspect a technical issue.

The project for the SSE dam must be based upon a geological survey.

The way the contour lines are displayed around the area in red in the following may suggest the rocks are not stable. i say that because the project water level stops where this kind of area begins.

 

 

And i cannot figure what the black dots represent.

Edited February 22, 2012 by michel123456

[Peter Dow]

Yep. This is the core of what we disagree about.

It's pretty hard to make an investment which you will only need in a decade from now.

Well the Bank of England is finding it very easy it seems to hand out free cash ("investment" is not quite the right word) to banks to try to breathe life into a UK stalled economy with plenty of spare productive capacity and high unemployment.

 

Quantitative easing

 

In October 2011, the Bank of England announced it would undertake another round of QE, creating an additional £75 billion,[46] and in February 2012 it announced an additional £50 billion,[47] bringing the total amount to £325 billion.

 

Now instead of wasting that on banker's bonuses and their jet-set life-style, I'll take oh £20 billion or so of government money to build this pumped-storage hydroelectric dam and there will be something to show for the money that will be of use not just in 10 years but for future generations.

 

I would advise all countries to consider the issue of energy storage though, and to scout for other locations for similar plans. The future will come eventually, so we will need additional storage.

 

I just don't think that the 1st purpose-built energy storage lake in Scotland should immediately solve all future problems.

Well my scheme won't solve all future problems but it helps more than the SSE scheme which in future will look like a missed opportunity because it occupies a site that could produce so much more.

 

Take it one step at a time.

My scheme is one step, it is just that it is a bigger, better step than the SSE scheme.

 

Surely there is some other glen, valley or lake in Scotland which you can use too?

This is the site up for public consultation. This is the time when a better plan for this site can be considered. Otherwise the SSE plan will be the only option for Coire Glas on the table.

 

The fair maiden Coire Glas is at the altar with her SSE suitor. So this is the time "to speak now or forever hold your peace".

Edited February 22, 2012 by Peter Dow

[Peter Dow]

I ment an elevation (or longitudinal section) of the dam.

 

Ah. How's this?

 

Cross section of the Dow-dam

The Dow-dam is more than 3 times higher than the SSE-dam. A horizontal line one third of the way up the Dow-dam indicates the relative height of the SSE dam although it is not aligned with this cross-section.

 

 

Image also hosted on PostImage.Org

 

Maps showing the line of cross-section viewed from each side

 

 

Image also hosted on PostImage.Org

 

 

Image also hosted on PostImage.Org

 

I'll answer your other points after I get some sleep.

[Peter Dow]

It has to be expected that your dam will have a vertical surface of about 5 times that of the original project.

Well without measuring the vertical surface areas I would estimate that a dam more than 3 times higher and twice as wide would be at least 6 times greater surface area.

 

If you expect twice the thickness (very conservative approach) your dam will be 10 times that of SSE.

No, I would expect a dam 3 times as high to be 3 times as thick, so the transverse cross-section would be 9 times the area. So then a dam twice as long would be 2 x 9 = 18 times the volume, 18 times the mass, 18 times the cost.

 

Also you must take into account that the water used to refill the damp must come from somewhere in the surroundings.

Loch Lochy. "Loch" is Scottish for "lake". There are many lochs in Scotland and the nearest one to Coire Glas happens to be called "Loch Lochy" which will be used as the lower reservoir for the SSE scheme and for my scheme though the additional volume of water in my scheme might require additional work on the Loch to facilitate the additional flows.

 

Have a look at the Grande Dixence dam in Switzerland, it is smaller than yours.

Nice.

 

Also i suspect a technical issue.

The project for the SSE dam must be based upon a geological survey.

The way the contour lines are displayed around the area in red in the following may suggest the rocks are not stable. i say that because the project water level stops where this kind of area begins.

 

 

And i cannot figure what the black dots represent.

Well here is an enhanced satellite photograph which will help to identify the geology of interest.

 

Enhanced satellite photograph

 

 

Image also hosted on PostImage.Org

 

From what you are saying Michel, it sounds like you have not looked at the site using Google Earth which provides a three dimensional view you can move around in, zooming in, rotating, very much like a video game. It is a very impressive tool.

 

I might be posting a video in future showing some views from Google Earth for those who can't manage to get it to work.

 

I suggest you have a good look if you can. I gave the Google Earth link for the site in my original post but here it is again.

 

Google Earth 3-D Coire Glas

Edited February 23, 2012 by Peter Dow

[michel123456]

No, I would expect a dam 3 times as high to be 3 times as thick, so the transverse cross-section would be 9 times the area. So then a dam twice as long would be 2 x 9 = 18 times the volume, 18 times the mass, 18 times the cost.

 

It does not seem to shock you. It even looks as if you liked that.

 

From what you are saying Michel, it sounds like you have not looked at the site using Google Earth which provides a three dimensional view you can move around in, zooming in, rotating, very much like a video game. It is a very impressive tool.

 

I might be posting a video in future showing some views from Google Earth for those who can't manage to get it to work.

 

I suggest you have a good look if you can. I gave the Google Earth link for the site in my original post but here it is again.

 

No, what you need is a geological map, most precisely a geological survey of the site.

 

-----------------

This is an example from a site for one of our projects. The yellow zone is practically (economically) a no-constructible area because the ground is unstable for a depth of 17 metres approx. I had no clue of that when looking at aerophotographs or even when visiting the site. The consulting geologist was very excited about the beauty of the phenomena...

 

The small black circles with a square are the points where the drilling took place. The black straight lines are section lines.

 

Edited February 24, 2012 by michel123456

[Peter Dow]

It does not seem to shock you. It even looks as if you liked that.

 

What's not to like about it?

 

I like spending money on something worthwhile like a big hydro scheme whereas I dislike the government wasting good public money on stupid bankers like this.

 

Quantitative easing

 

In October 2011, the Bank of England announced it would undertake another round of QE, creating an additional £75 billion,[46] and in February 2012 it announced an additional £50 billion,[47] bringing the total amount to £325 billion.

 

As I said to CaptainPanic.

Now instead of wasting that on banker's bonuses and their jet-set life-style, I'll take oh £20 billion or so of government money to build this pumped-storage hydroelectric dam and there will be something to show for the money that will be of use not just in 10 years but for future generations.

 

 

No, what you need is a geological map, most precisely a geological survey of the site.

-----------------

This is an example from a site for one of our projects. The yellow zone is practically (economically) a no-constructible area because the ground is unstable for a depth of 17 metres approx. I had no clue of that when looking at aerophotographs or even when visiting the site. The consulting geolog was very excited about the beauty of the phenomena...

 

The small black circles with a square are the points where the drilling took place. The black straight lines are section lines.

 

 

I don't need a geological map at the early stage of presenting a vision for building a dam and excavating a reservoir bed.

 

I think it reasonable to assume that the geology would be favourable for my scheme since the SSE have determined that the geology is favourable for their scheme on the same site.

 

I did clearly say in an earlier post that my vision for the excavated reservoir bed considered both the case of very stable bed rock and unstable ground. Remember?

 

Excavated Reservoir Bed

 

The green ellipse of major diameter of 1.5 kilometres and minor diameter of 1 kilometre represents an excavated reservoir bed, as flat and as horizontal as practical, at an elevation of 463 metres.

 

Since an excavated reservoir bed is not, that I can see, part of the SSE plan, at any size, I will provide some more information about my vision for that now.

 

The basic idea of excavating a flat or flattish reservoir bed is to increase the volume of the water stored in the reservoir because more water means more energy can be stored.

 

Depending on the geology and strength of the rock of Coire Glas the walls of the reservoir bed perimeter could be as steep as vertical from the reservoir bed up to the natural elevation of the existing rock surface which would mean, presumably, blasting out rock to create a cliff which at places could be as much as about 290 metres tall.

 

Near the dam, the reservoir bed perimeter wall would be only 40 metres or less tall. The further from the dam, the higher the wall will be and the more rock needs to be excavated.

 

A vertical reservoir bed perimeter wall would be ideal to maximise reservoir volume wherever the geology provides a strong stone which can maintain a vertical wall face without collapse, (a stone such as granite perhaps).

 

Where the geology only provides a weaker stone then a sloping perimeter wall at a suitable angle of repose for reliable stability would be constructed.

 

So the reservoir perimeter wall could be as sloped as shallow as 45 degrees from the natural elevation at the perimeter of the eclipse sloping down to the reservoir bed at 463 metres elevation in the case of the weakest and most prone to collapse kinds of stone.

 

Exactly how strong the stone is at each location I guess we'll only find out absolutely for sure if and when engineers start blasting it and testing the revealed rock wall face for strength.

 

The shape of the perimeter of the excavated reservoir bed is not absolutely critical. So long as it ends up as a stable wall or slope, however it is shaped by the blasting, it will be fine. There is no need to have stone masons chip the perimeter smooth and flat! The ellipse is simply the easiest approximate mathematical shape to describe and to draw. If the end result is not a perfect ellipse, don't worry, it will be fine!

 

And in a later post I illustrated the options for the reservoir perimeter wall - vertical, sloping at 45 degrees or somewhere in between with a diagram.

 

Cross section of the Dow-dam reservoir

 

 

Cross section along the major diameter of the elliptical excavation of the reservoir bed

 

Also hosted on PostImage.org

 

I hope that is clear now.

Edited February 24, 2012 by Peter Dow

[Peter Dow]

Now if my proposed far larger dam stored 6 times the energy (twice the area and 3 times the depth of water equals 6 times the volume of water) that would still only be 3 hours supply at 63 gigawatts and the wind is becalmed for far longer than that.

 

So there is no risk that this will be too big. There is a certainty that it will not be enough but it is a start.

I need to update my estimates for the energy stored by my scheme. Now I'm thinking 20 times more energy could be stored than the SSE plan offers.

 

It now looks like 600 Giga-Watt-Hours is achievable!

 

My dam is more like 3.44 times higher not just "3 times" higher than SSE's dam.

My dam is more like 2.27 times longer not just "2 times" longer than SSE's dam.

 

A greater percentage of the water in my reservoir achieves maximum depth because of the excavated reservoir bed.

 

My calculations indicate that the volume of water in my reservoir when full would be about 400 million cubic metres and its centre of mass would be 569 metres above the lower reservoir which gives a theoretical potential energy in excess of 600 GW-Hrs!

 

Now allowing for turbine efficiency of 90% but remembering that more rock could be excavated perhaps around the perimeter to further increase water volume then it is possible that a genuine 600 GW-Hours could be available as supplied power at Coire Glas!

 

My bigger plan for Coire Glas offers about 20 times more energy stored, than the SSE's plan of only 30 GW-Hrs.

 

600 GW-hours is enough for 100 hours of supply at 6 GW - keeping the lights on in Scotland, using only renewable energy.

 

 

See this power-flow map for Britain I found recently which gives peak power flows and I assume the figures are MegaWatts.

 

Power flow map source - National Grid. Effect on Power Transfers

 

But a 600 GW-hr energy store at Coire Glas could also supply 8.5 GW for 70 hours or 12 GW for 50 hours - and that would be very useful too, for two reasons.

 

1. Providing an energy store for the grid in England.

 

2. Providing more heat energy in Scotland from renewables as well, so that we can offer consumers a cheaper alternative to gas, coal and oil heating of homes, offices etc.

 

For those two reasons, I would install 12 GW generators and transmission capacity for my Coire Glas hydro scheme alone.

 

After my Coire Glas project next we'd have the option of building a few more pumped-storage schemes the size of my plan for Coire Glas and then Scotland could provide energy storage facilities -

 

• Either for all of the "British national" grid
  
• Or to make profits for an independent Scottish economy by energy import/export.

 

Whatever the politics, Scotland has the geography to site pumped storage hydro dam schemes to supply renewable energy 100% of the time.

 

The investment required can come from re-allocating Bank of England "quantitative easing" cash and this is the way to go to get 100% renewable energy supplied under all circumstances.

 

No, I would expect a dam 3 times as high to be 3 times as thick, so the transverse cross-section would be 9 times the area. So then a dam twice as long would be 2 x 9 = 18 times the volume, 18 times the mass, 18 times the cost.

I need to update that too. My dam would be 3.44 times as high and as thick, 11.8 times the cross-sectional area, 2.27 times as long so about 27 times the volume, the mass and the cost.

 

Loch Lochy. "Loch" is Scottish for "lake". There are many lochs in Scotland and the nearest one to Coire Glas happens to be called "Loch Lochy" which will be used as the lower reservoir for the SSE scheme and for my scheme though the additional volume of water in my scheme might require additional work on the Loch to facilitate the additional flows.

 

It turns out the additional flows to and from the Loch is a much bigger issue than I first thought. The volume in the dam is more than I thought and the surface area of Loch Lochy is less than I had assumed, only some 16 kilometres squared. This means I'd need the top 25 metres of water (at least) from the Loch to fill my dam! Hmm.

Edited March 5, 2012 by Peter Dow

[Peter Dow]

It turns out the additional flows to and from the Loch is a much bigger issue than I first thought. The volume in the dam is more than I thought and the surface area of Loch Lochy is less than I had assumed, only some 16 kilometres squared. This means I'd need the top 25 metres of water (at least) from the Loch to fill my dam! Hmm.

 

Loch Lochy and vicinity water flow control works

 

Here is an annotated satellite photograph of the land south from Coire Glas showing Loch Lochy, Loch Arkaig, the isthmus between the lochs, Mucomir where Loch Lochy empties into the River Spean before it flows on as the River Lochy, the Caledonian Canal and Fort William where the river flows into a sea loch.

 

 

Click to see larger image

 

New waterway

 

Loch Lochy is separated from a neighbouring loch, Loch Arkaig, by a 2 km wide isthmus, which I have identified on this map as "the Achnacarry Bunarkaig isthmus", after the local place names.

 

It ought to be quite straight forward to build a canal or culvert, to connect those two lochs. The idea is that the new waterway would be wide and deep enough, enough of a cross section area under water, perhaps hundreds of square metres, so as to allow free flow from one loch to the other, so as to equalise the surface elevations of the two lochs, so as to increase the effective surface area of Loch Lochy so as to decrease the depth changes to Loch Lochy when water flows in from the Coire Glas reservoir when it discharges water when supplying power.

 

Now, Loch Arkaig has a natural surface elevation of 43 metres and this would be lowered to that of Loch Lochy. The surface area of Loch Arkaig is given by wikipedia as 16 km^2 also, (though it looks to me somewhat smaller than Loch Lochy). In addition, partially draining Loch Arkaig to bring its level down to that of Loch Lochy will also reduce its surface area.

 

If say, the additional surface area of Loch Arkaig is about 10 km^2 added to Loch Lochy's 16 km^2 this would give an effective surface area of 26 km^2 and reduce the potential depth variation to

 

Potential depth variation of Loch Lochy + Loch Arkaig = 400 000 000 m^3 / 26 000 000 m^2 = 15.3 metres.

 

Without equalising the loch levels, the depth changes to Loch Lochy that would require to be managed may be potentially more like 25 metres than 15 metres. So the new waterway is an important part of the new water flow control works that Coire Glas/Dow requires to be constructed.

 

Additional Loch Lochy water level control measures

 

When the Coire Glas reservoir is full, then the water level of Loch Lochy should be prevented, by new water works - drains, dams, flood barriers etc. - from rising due to rainfall and natural flow into the loch above a safe level which allows for the reservoir to empty into the loch without overflowing and flooding.

 

The safe "upper-reservoir-full" loch level will likely turn out to be around about 15 metres below the maximum loch level.

 

The next diagram showing the new loch drain and the reservoir pump inlets indicates how this might be achieved.

 

 

Click to see larger image

 

The drain from Loch Lochy to the sea which goes underground from the 14 m elevation level in the loch would need capacity for the usual outflow from Loch Lochy which currently goes through the Mucomir hydroelectric station.

 

I have estimated the flow through Mucomir from its maximum power of 2MegaWatts and its head of 7m as somewhere near 0.2 Mega-cubic-metres-per-hour and compared that value using a spreadsheet I have written to predict the capacity of water flow through different sizes of drains using the empirical Manning formula and this is also useful for determining the appropriate size of the new water channel between the lochs.

 

 

Ease my quantity

 

To construct Coire Glas/Dow/600GW.Hrs/12GW may cost of the order of around £20 billion, but that would be my order of magnitude educated guess more than a professional cost estimate.

 

In other words, I'm only really confident at this early "vision" stage that the cost would be closer to £20 billion than it would be to £2 billion or to £200 billion but I'm not claiming to be able to quote an accurate cost estimate at this stage.

 

I have not itemised my costs - how much for land, how much for labour, how much for trucks, how much for diggers, how much for cement, how much to install the generators etc. and the SSE have not published itemised costs for theirs either so I can't calculate my costs in a proportion to the SSE's costs.

 

Although my version offers 600 GigaWatt-Hours energy and 12 GigaWatts power (or 20 times the capacity and performance) some of the items in my version would cost more than "in proportion", in other words more than 20 times the SSE's cost.

 

For example, the cost of my dam will be more like 27 times the cost of the SSE's dam. (3.44 times higher and thicker and 2.27 times longer).

 

For example, the cost of excavating 400 million tonnes of rock from the reservoir bed to increase the capacity of the reservoir to hold water (and energy) in my version won't be in proportion to the SSE costs for excavating their reservoir bed because, as far as I know, they don't plan to excavate their reservoir bed at all.

 

On the other hand, my land costs are about the same as the SSE's - much less than in proportion. I may well need to use more land to dispose of the additional excavated rock spoil but perhaps when that additional land has been landscaped over it could be resold?

 

So it depends how much the land is as a proportion of the SSE's costs. If land is a small part of their costs, if 20 similar sites to build on are just as cheap and easy to buy then my costs will be much more than proportional, since saving land won't save much money.

 

If land is scare and valuable and the cost to purchase suitable land with a good chance to get permission to build on it is a significant proportion of the SSE's or anyone's costs to build 20 of their size of hydro dam schemes then my costs may be better than proportional. Sometimes securing suitable land for development can be very problematic, very expensive. Sometimes people won't sell their land. Sometimes the authorities won't agree that the land can be used in this way.

 

The SSE say that suitable sites for such pumped storage schemes are rare indeed, so land costs may be very significant and my scheme good value for money.

 

If indeed the cost of my scheme is somewhere around £20 billion it is likely to cost far more than the SSE or any electrical power supply company looking to their annual profits for the next few years could possibly afford.

 

Something like £20 billion I expect could only be found as a national public infrastructure project, spending government money, like the building of a large bridge or motorway would be.

 

A £20 billion government project would require Treasury approval, at least while Scotland is ruled as part of the UK.

 

I have suggested funding my much larger hydro dam scheme by re-allocating of some of the Bank of England's "Quantitative Easing" funds which amount to some £300 billion of new money printed with not much to show for it.

[Peter Dow]

No, what you need is a geological map, most precisely a geological survey of the site.

 

 

Geology of the Coire Glas site

I have been able to extract this information from the British Geological Survey (BGS) Geology of Britain viewer, from the 1:50 000 scale map.

 

 

Click to see larger image

 

According to this map, the bedrock at the site which would be used to build the dam on top of and to extract rock from to create the tunnels for the underground complex seems to be a rock geologists call "psammite" which I understand to mean here "a metamorphic rock whose protolith was a sandstone".

 

What neither the map nor the "psammite" name is telling us is how fractured the psammite rock there is and therefore how strong and also how impermeable or otherwise to water this rock is likely to prove to be, both of which would be interesting for any engineers building a pumped-storage hydro dam scheme there to know.

 

What does look fairly obvious to me is that the superficial deposit of what the map calls "hummocky (moundy) glacial deposits - diamicton, sand and gravel" would not be strong enough, nor impermeable enough to build any dam on top of and at least along the line of the dam, this glacial deposit ought to be removed to get down to the bedrock within which to establish the foundations of the dam, although I would think that this glacial deposit might be made into aggregate to make the concrete for the dam by the sounds of it.

Edited March 16, 2012 by Peter Dow

[Peter Dow]

Dam foundations and height of the dam above the bedrock

The top of the Dow-Dam has an elevation of 780 metres by design.

 

 

Image also hosted here

 

The lowest elevation of the current ground surface of Coire Glas along the line of the proposed dam is 463 metres and subtracting 463 from 780 is how the initial value of 317 metres for the nominal height of the dam above the existing surface used in previous diagrams was arrived at.

 

However, the glacial deposit of as yet unknown thickness is to be removed before building the foundations of the dam within and upon the bedrock.

 

Although the lowest surface elevation along the line of the dam of the bedrock too is unknown a formula relating the Height of the Dam Above the Bedrock (HDAB) to the Glacial Deposit Depth (GDD) can be easily stated.

 

HDAB = 317 + GDD

 

Examples.

 

If the GDD turns out to be 13 metres then the dam will be 330 metres tall.

If the GDD turns out to be 83 metres then the dam will be 400 metres tall.

 

 

Image also hosted here

 

I propose that the height of the Dow-Dam be as tall above the bedrock as it needs to be to keep the top of the dam at an elevation of 780 metres no matter how deep the removed glacial deposit layer turns out to be.

 

My approach may well differ from the SSE's approach. The SSE have said that their dam will be "92 metres" high and they may stick to that without having any goal for the elevation of the top of their dam.

 

As the diagram indicates, I propose to secure the Dow-Dam to the bedrock by massive piles inserted and secured into shafts which would be drilled into the bedrock.

Edited March 17, 2012 by Peter Dow

[Peter Dow]

http://www.youtube.com/watch?v=asUa1PFix1A

Video which illustrates the principle of using wind turbines and pumped storage hydro dam schemes together.

[Peter Dow]

"Dow" equation for the power and energy output of a wind farm.

 

"The power and energy of a wind farm is proportional to (the square root of the wind farm area) times the rotor diameter".

 

In his book which was mentioned to me on another forum and so I had a look, David MacKay wrote that the power / energy of a wind farm was independent of rotor size which didn't seem right to me considering the trend to increasing wind turbine size.

 

Now I think the commercial wind-turbine manufacturing companies know better and very possibly someone else has derived this equation independently of me and long ago - in which case by all means step in and tell me whose equation this is.

 

Or if you've not see this wind farm power/energy equation before, then see if you can figure out my derivation!

[Peter Dow]

No takers for the derivation challenge huh? OK then.

 

Derivation

 

Assume various simplifications like all turbine rotors are the same size and height, flat ground and a rotationally symmetrical wind turbine formation so that it doesn't matter what direction the wind is coming from.

 

Consider that an efficient wind farm will have taken a significant proportion of the theoretically usable power (at most the Betz Limit, 59.3%, apparently, but anyway assume a certain percent) of all the wind flowing at rotor height out by the time the wind passes the last turbine.

 

So assume the wind farm is efficient or at least that the power extracted is proportional to the energy of all the wind flowing through the wind farm at rotor height.

 

This defines a horizontal layer of wind which passes through the wind farm of depth the same as the rotor diameter. The width of this layer which flows through the wind farm is simply the width of the wind farm which is proportional to the square root of the wind farm area.

 

Wind farm turbine formations

 

Therefore the width or diameter of a rotationally symmetrical wind farm is a critically important factor and arranging the formation of wind turbines to maximise the diameter of the wind farm is important.

 

Consider two different rotationally symmetrical wind turbine formations, I have called the "Ring formation" and the "Compact formation".

 

Let n be the number of wind turbines in the wind farm

Let s be the spacing between the wind turbines

 

Ring formation

 

 

Larger image also hosted here

 

The circumference of the ring formation is simply n times s.

 

Circumference = n x s

 

The diameter of the ring formation is simply n times s divided by PI.

 

Diameter = n x s / PI

 

Compact formation

 

 

Larger image also hosted here

 

The area of the compact formation, for large n, is n times s squared. This is slightly too big an area for small n.

 

Area = n x s^2 (for large n)

 

The diameter of the compact formation, for large n, is 2 times s times the square root of n divided by PI. This is slightly too big a diameter for small n.

 

Diameter = 2 x s x SQRT(n/PI)

 

This is easily corrected for small n greater than 3 by adding a "compact area trim constant" (CATC) (which is a negative value so really it is a subtraction) to the s-multiplier factor.

 

The CATC is 4 divided by PI minus 2 times the square root of 4 divided by PI.

 

CATC = 4/PI - 2 x SQRT(4/PI) = - 0.9835

 

This CATC correction was selected to ensure that the compact formation diameter equation for n=4 evaluates to the same value as does the ring formation equation for n = 4, that being the largest n for which the ring and compact formations are indistinguishable.

 

The CATC works out to be minus 0.9835 which gives

 

Diameter = s x ( 2 x SQRT(n/PI) - 0.9835) (for n > 3)

 

Ratio of diameters

 

 

Larger image also hosted here

 

It is of interest to compare the two formations of wind farm for the same n and s.

 

The diameter of the ring formation is larger by the ratio of diameter formulas in which the spacing s drops out.

 

Ring formation diameter : Compact formation diameter

 

n/PI : 2 x SQRT (n/PI) - 0.9835

 

This ratio can be evaluated for any n > 3 and here are some ratios with the compact value of the ratio normalised to 100% so that the ring value of the ratio will give the ring formation diameter as a percentage of the equivalent compact formation diameter.

 

Here are some examples,

 

n = 4, 100 : 100

n = 10, 123 : 100

n = 18, 151 : 100

n = 40, 207 : 100

n =100, 309 : 100

n =180, 405 : 100

n =300, 514 : 100

n =500, 656 : 100

 

As we can see that for big wind farms, with more turbines, the ratio of diameters increases.

 

Since the Dow equation for the power and energy of a wind farm is proportional to the diameter of the wind farm then it predicts that the power and energy of the ring formation wind farms will be increased compared to the compact formation wind farms by the same ratio.

 

In other words, the Dow equation predicts, for example, that a 100 turbine wind farm in the ring formation generates 3 times more power and energy than they would in the compact formation, assuming the spacing is the same in each case.

 

Practical application when designing a wind farm

 

My recommendation would be to prefer to deploy wind turbines in a wind farm in the ring formation in preference to the compact formation all other things being equal.

 

The compact formation can be improved up to the performance of a ring formation by increasing the turbine spacing so that the circumference is as big as the ring but then if a greater turbine spacing is permitted then the ring formation may be allowed to get proportionally bigger as well keeping its advantage, assuming more area for a larger wind farm is available.

 

The ring formation may be best if there is a large obstacle which can be encircled by the ring, such as a town or lake where it would not be possible or cost effective to build turbines in the middle of it and so a compact formation with larger spacing may not be possible there.

 

Where it is not possible to install a complete ring formation then a partial ring formation shaped as an arc of a circle would do well also.

[Peter Dow]

Reservoir bed drain

 

The high pressure of water which is deeper than 100 metres has the potential to induce seismic activity or earthquakes in susceptible rock in which a new reservoir has been constructed.

 

Wikipedia: Induced seismicity - Causes - Reservoirs.

 

The mass of water in a reservoir alters the pressure in the rock below and through fissures in the rocks' date=' lubricates the fault, which can trigger earthquakes.

...

Unfortunately, understanding of reservoir induced seismic activity is very limited. However, it has been noted that seismicity appears to occur on dams with heights larger than 100 meters. The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity.[/quote']

 

Coire Glas/SSE/92 m

 

Hopefully, reservoir induced seismicity was an issue considered by the SSE when selecting Coire Glas for their hydro dam project.

 

I am speculating that this issue may be why the SSE have limited their dam to a height and their reservoir to a depth of 92 metres?

 

I would note however that the pressure in the head race tunnels which supply water from the reservoir to the turbines would be proportional to their depth below the surface of the reservoir and this could be as much as 500 metres deep, so there would seem to be some potential for water to penetrate the bed rock from the high pressure water tunnels and induce seismic activity even in the SSE case.

 

This is an issue which ought to have been addressed in the many previous pumped-storage hydro scheme projects, most of which seem to have a difference in head of more than 100 metres.

 

Given that "understanding ... is very limited" according to Wikipedia, though, I do wonder if the reservoir induced seismicity issue has not always been properly addressed in all previous dam and reservoir construction schemes where the great depth of water and susceptible geology ought to make it a relevant concern?

 

Coire Glas/Dow/317+m

 

I am proposing measures to counter the reservoir induced seismicity effect in the case that the geology of Coire Glas is susceptible to it and in the general case.

 

I propose the construction of a large reservoir surface drain to cover the whole reservoir bed and the reservoir sides too to try to stop the penetration of water under high pressure into fractures in the bedrock and so thereby stop this high pressure water from widening and extending bedrock fractures.

 

To illustrate my "reservoir bed drain" concept, I have drawn a diagram comparing the usual no drain on the left, with my proposed reservoir bed drain on the right.

 

 

Image also hosted here.

 

So my idea is that the top layer of the drain is as impermeable as practical, using perhaps a layer of reinforced asphalt concrete.

 

In engineering practice I believe that impermeable reservoir bed layers have used clay or clay with asphalt or even rubberised asphalt mixed with sand.

 

My basic idea is to construct an impermeable layer and to use whatever material is best for that.

 

Then working downwards, the permeable drain layers are increasingly bigger loose particles, with sand at the 2nd top then beneath that grit, then gravel, then small stones and finally below all those a layer of large stones.

 

The higher layers support the top impermeable layer which is under high pressure from the reservoir water and the lower permeable layers provide many small channels for any (hopefully tiny amounts of) water which forces its way through the supposedly impermeable top layer to drain down the slope of the reservoir bed out under the dam.

 

The bottom layer is another impermeable layer to try to make doubly sure that the relatively low pressure water that gets into the drain will find its way out under the dam by following the course of the drain.

 

These kinds of layers of different sized loose particles have previously been used to make simple narrow drains and impermeable layers have been added to reservoir beds before now but whether professional dam engineers have ever covered the entire reservoir bed and sides with one large drain I don't know. If not, this could be named the "Dow drain" solution to reservoir induced seismicity!

[Peter Dow]

My second take is to use drain-pipes through the base of the dam which now extends all the way down to the bed rock with the drain-pipes built in, instead of continuing the bed drain under the dam as I had at first.

 

The large embedded image in the above post is remotely hosted on my forum so I was able to change that there. However, it is too late now to edit the above post to change the small image and the link to the postimage.org host and neither can I change the attached image.

 

So I am posting the new versions now.

 

Image also hosted here.

 

Why not add a simple impermeable layer to the reservoir bed?

 

I think the additional complexity and expense of a bed drain (and drains for the sides too) is better than simply adding an impermeable layer.

 

Consider the fault condition of the two possible solutions.

 

If a simple impermeable layer fails, if it cracks or ruptures or disintegrates under the pressure changes, how would anyone know? It may look fine but be leaking high pressure water into the bedrock and inducing seismicity which OK the engineers would notice any earthquakes but so would everyone else, the earthquakes could cause damage or loss of life and it could lead to a loss of confidence in the project and in the engineers who built it. They could go to jail!

 

If the top impermeable layer of the bed drain fails then there would be some water pouring out of the drainpipes through the base of the dam when at most it should only be a tiny trickle of water. So the engineers would know there was a problem with the bed drain and they'd know to drain the reservoir and fix or replace the top supposedly "impermeable" layer, fix the bed drain so that it operated as it should.

 

So failure with the bed drain is noticed right away and it is not a catastrophic failure. Whereas failure with the simple impermeable layer may not be noticed until a catastrophic earthquake happens.

 

So this is why I think the bed drain is worth the extra complexity and expense. It is a more fault tolerant engineering solution.

Edited March 30, 2012 by Peter Dow