Observations Dam Levels & Water Usage; A Discussion

Ken Kato

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Just thought I'd create a new thread as a single place for people to discuss anything to do with dam levels, water usage, etc in QLD.

I probably won't be a regular contributor to this thread but it's here for anyone who wants to talk about it.
 

Ken Kato

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@Ken Kato geographics might be a bit narrow? I know @Snow Blowey knows a bit about this but is usually found a bit further south.
It was actually my original intention to have it focus on QLD and NE NSW @Fozzie Bear because there's been a lot of talk about it in the day to day thread for SE QLD/NE NSW (which now also has a number of Central QLD people in it). And also so the convo doesn't get too disjointed and hard to follow if there's lots of posts from vastly different regions.

But if you or others think that it should be expanded to cover all of NSW as well as QLD, or the entire country for that matter, I'm more than willing to change the title if you like?
 

Fozzie Bear

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It was actually my original intention to have it focus on QLD and NE NSW @Fozzie Bear because there's been a lot of talk about it in the day to day thread for SE QLD/NE NSW (which now also has a number of Central QLD people in it). And also so the convo doesn't get too disjointed and hard to follow if there's lots of posts from vastly different regions.

But if you or others think that it should be expanded to cover all of NSW as well as QLD, or the entire country for that matter, I'm more than willing to change the title if you like?

I guess there is a lot of interaction from what happens in Queensland with the Murray Darling basin (for one), hence the state borders being a bit redundant?
 
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Snow Blowey

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I guess the main separation and biggest point of confusion for people on the coast is the difference between the coastal dams and the inland ones. The coastals being primarily for town water supply and the inland dams being for primary industries, as well as supplying plenty of water for towns that rely on them.

For example, it came up in the drought a couple of years back that Dubbo was in dire straights because Burrendong Dam was at 3%. But that was a few years town supply for Dubbo and other reliant downstream towns. Not to mention supplimentry sources of groundwater along the major river systems.
 

Flowin

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I guess the main separation and biggest point of confusion for people on the coast is the difference between the coastal dams and the inland ones. The coastals being primarily for town water supply and the inland dams being for primary industries, as well as supplying plenty of water for towns that rely on them.
It is quite different in Qld - there are many coastal dams east of the GDR for irrigation and industry - and some west of the GDR for town water supply - so it is a real mixed bag.
It was actually my original intention to have it focus on QLD and NE NSW @Fozzie Bear because there's been a lot of talk about it in the day to day thread for SE QLD/NE NSW (which now also has a number of Central QLD people in it). And also so the convo doesn't get too disjointed and hard to follow if there's lots of posts from vastly different regions.

But if you or others think that it should be expanded to cover all of NSW as well as QLD, or the entire country for that matter, I'm more than willing to change the title if you like?
I agree the water situation discussed in the SEQ NE NSW thread needed another topic.

@Ken Kato geographics might be a bit narrow? I know @Snow Blowey knows a bit about this but is usually found a bit further south.
If broader scale, this discussion could get quite lively (a good thing), maybe difficult to follow ( a not so good thing), and could possibly even overtake the marathon 335 pages (as at today) of the NSW/Qld weather thread LOL
 
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Legs Akimbo

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We could start with over allocation along the MDB.
Richard Beasley, who was counsel assisting Bret Walker in the SA Royal Commission into the Murray Darling, has written a book about the river called Dead In the Water about the circus that is water allocation. Surprisingly entertaining and quite devastating in its criticism.
 

warrie

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Current level of the Darling at Bourke - behind the weir, that's just a small dam and totally apolitical http://www.bom.gov.au/fwo/IDN60238/IDN60238.548004.plt.shtml

Post by Legs quite helpful actually. IMO
IDN60238.548004.png
 

Snow Blowey

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Data without context is meaningless.

Not sure what your point is.

Its summer and there hasn't been any significant widespread rain events. Lots of regular smaller events well spaced. So all the water is staying in the landscape. Even in the Macquarie we are having a cracker summer but the rain keeps coming in fortnightly intervals with falls of around 20-30mm. Enough for the ground and plants to use without major runoff.

Not much flow in any of the major contributors to the Darling (Namoi, Gwydir, Border Rivers, Condamine Ballone, Warrego etc.)

There has been very little inflow to the northern NSW dams that feed the Darling. Basically there is no substantial natural flow in any of the basin at present. Likely to be different this time next week.
 
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Flowin

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Wivenhoe Dam for SEQ is currently around 36% and needs around 600,000 ML to fill the water supply portion of the dam.
Today's BoM update of seasonal streamflow forecast for Gregor Creek gauge on the upper Brisbane River doesn't show much hope of filling.
Only about 10% chance of exceeding 50,000 ML for March to May 2021.
Gregor's Creek gauge catchment is about 70% of the upper Brisbane River catchment to Wivenhoe Dam (excluding the catchment of Somerset Dam)

143009A_FC_12_2021_03.png
 

Locke

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When the FSL was changed to 75% for Wivenhoe following the 2011 Brisbane floods I thought at the time this was a terrible idea that was failing to take into account the lessons of the past regarding how frequently major inflow events occur within the Somerset and Wivenhoe catchments.

I saw a paper, which is no longer available online, that noted on 3 occasions in the 20th century, the Wivenhoe catchment area went for a period in excess of 10 consecutive years without significant inflow events. Given the Wivenhoe currently uses 10-15% of its capacity each year if there is no significant inflow that raised a massive risk of the dam running dry in the absence of crippling water restrictions.
 

warrie

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Currently it is over 96% full, if the forecast's come off I would expect quite a substantial spill by some time Friday or Saturday.
Katoomba forecast is 108 mm min to a max of 190 mm thru till Tuesday, but Goulburn only 32 to 72 mm. One assumes that somewhere in the Sydney Water hydrology office someone is sweating over these and other numbers. Will a pre-release occur since there's only 80 GL of airspace?
 
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Mogul

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Katoomba forecast is 108 mm min to a max of 190 mm thru till Tuesday, but Goulburn only 32 to 72 mm. One assumes that somewhere in the Sydney Water hydrology office someone is sweating over these and other numbers. Will a pre-release occur since there's only 80 GL of airspace?
Water NSW have always said Warragamba is for drinking water storage and not flood mitigation, so what happens downstream during release's is not their problem. One would think there has to be some pre planning for these sorts of events, but how much do you let out prior is the big question.
 

Flowin

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Katoomba forecast is 108 mm min to a max of 190 mm thru till Tuesday, but Goulburn only 32 to 72 mm. One assumes that somewhere in the Sydney Water hydrology office someone is sweating over these and other numbers. Will a pre-release occur since there's only 80 GL of airspace?

Water NSW have always said Warragamba is for drinking water storage and not flood mitigation, so what happens downstream during release's is not their problem. One would think there has to be some pre planning for these sorts of events, but how much do you let out prior is the big question.

Warrie, Mogul, the issue of pre-release from a dam to potentially reduce flooding just before a flood event is a treacherous matter if there are significant catchments downstream of the dam.
The issue is not just about wasting water but equally, or more importantly, about significant potential to make flooding worse downstream of the dam compared to if no pre-releases occur.
Flooding downstream of Warragamba dam is not just from the dam outflows but also other catchments joining downstream as well.
Pre-releases free up dam space but also the released water is still travelling down the river when the rain comes - so if rain falls downstream of the dam on top of a river that has raised levels because of the pre-releases the flooding can be made worse.
Below is the Access G forecast 12Z for 3 day rain from 2200 AEST 18 March to 21 March with the Warragamba Dam catchment shown - it shows a significant area of the heaviest predicted rain being downstream of the dams - it would be potentially dangerous to pre-release in that situation.

But also I find such single images of forecast rainfall can be quite misleading, because the forecasts are often not accurate for where the heaviest rainfall will be.
The second animated image below is the same time period and same area (image is smaller to save file size) but instead shows each of fifty the EC ensemble members to demonstrate the uncertainty in the location and amount of the heaviest rainfall. When that is taken into account it is very difficult to be sure of rainfall upstream versus downstream of the dam.

Gotta say though you guys in NSW seem to have better consistency in forecasts with less location error than forecasts we get for SEQ which often resemble a "bingo board" (wide displacement error) for where heavy rain will be.
Anyway a lot of people think dams should pre-release based on forecasts, but unless the rain positioning is accurate it is a difficult matter to judge with the possibilities of worse flooding outcomes.

access G 2200 18 March to 2200 21 March with Warragamba Dam catchment.png

Warragamba EC 50member ensemble 20210318 12Z 3 day rain 2200 to 2200 AEST 21 March 2021.gif
 

Gimped

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Currently it is over 96% full, if the forecast's come off I would expect quite a substantial spill by some time Friday or Saturday.
It's spilling now (the dams will never fill again!).
 

Ding

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It's spilling now (the dams will never fill again!).

Serious question, if the government can impose water restrictions, ie can't water your plants or hose your car or yard, when the dam levels are sub 50% capacity, would it make sense to ask us to keep our taps on when the dams are close to spilling?

Like just ask people to fill their bath tubs and drain the water a number of times for no good reason other than to suck water out of system. Will that ease the dam levels?
 

Snow Blowey

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Serious question, if the government can impose water restrictions, ie can't water your plants or hose your car or yard, when the dam levels are sub 50% capacity, would it make sense to ask us to keep our taps on when the dams are close to spilling?

Like just ask people to fill their bath tubs and drain the water a number of times for no good reason other than to suck water out of system. Will that ease the dam levels?

Your pipes don't go directly to warragamba. Pipes to prospect res to treatment to plumbing. And the dribble out of your tap will be insignificant compared to the hundreds of thousands of megalitres that will be going down the Nepean tomorrow.
 
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Majikthise

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Warrie, Mogul, the issue of pre-release from a dam to potentially reduce flooding just before a flood event is a treacherous matter if there are significant catchments downstream of the dam.
The issue is not just about wasting water but equally, or more importantly, about significant potential to make flooding worse downstream of the dam compared to if no pre-releases occur.
Flooding downstream of Warragamba dam is not just from the dam outflows but also other catchments joining downstream as well.
Pre-releases free up dam space but also the released water is still travelling down the river when the rain comes - so if rain falls downstream of the dam on top of a river that has raised levels because of the pre-releases the flooding can be made worse.
Below is the Access G forecast 12Z for 3 day rain from 2200 AEST 18 March to 21 March with the Warragamba Dam catchment shown - it shows a significant area of the heaviest predicted rain being downstream of the dams - it would be potentially dangerous to pre-release in that situation.

But also I find such single images of forecast rainfall can be quite misleading, because the forecasts are often not accurate for where the heaviest rainfall will be.
The second animated image below is the same time period and same area (image is smaller to save file size) but instead shows each of fifty the EC ensemble members to demonstrate the uncertainty in the location and amount of the heaviest rainfall. When that is taken into account it is very difficult to be sure of rainfall upstream versus downstream of the dam.

Gotta say though you guys in NSW seem to have better consistency in forecasts with less location error than forecasts we get for SEQ which often resemble a "bingo board" (wide displacement error) for where heavy rain will be.
Anyway a lot of people think dams should pre-release based on forecasts, but unless the rain positioning is accurate it is a difficult matter to judge with the possibilities of worse flooding outcomes.

access G 2200 18 March to 2200 21 March with Warragamba Dam catchment.png

Warragamba EC 50member ensemble 20210318 12Z 3 day rain 2200 to 2200 AEST 21 March 2021.gif
Warragamba could operate at a lower FSL which is a much better strategy than short term pre release
 
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Snow Blowey

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Yep almost every other option is better than pre release just before a flood. With a lower FSL it would spill more often but there could be more scope to reduce magnitude of peak spill flows.


As with all things whoever makes any decision will be told they were wrong a week or so after the fact. Lower early and you'll get the blame for no water in storage if the rain doesn't come. Go late and you caused the flood. Same situation as the guys in Brisbane faced.

The upward opening gates offer some additional flood mitigation. By releasing at the bottom of the gate you raise the height of the dam.
 

art

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All running as it should be there is low risk of blame for those making decisions during an event. The dams have an operation plan and if it is followed then any blame ultimately gets directed to those that made and approved the plan.
If I recall correctly the plan was not followed in Brisbane.

The balance between flood mitigation and water supply storage is a decision made long ago and on the public record.
 
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art

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The upward opening gates offer some additional flood mitigation. By releasing at the bottom of the gate you raise the height of the dam.
I don't think this offers any more flood storage. When you raise the gate so they don't overtop water comes out under them. This would be roughly equivalent to what would flow over the top.
Yes there is flood storage beyond the top of the gates but no different than a fixed spillway at the same height.
The advantage of the gates is the operators can increase release if needed, I doubt they will be keen to do that today beyond what they may be forced to do to stop the gates being overtopped.
 
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Snow Blowey

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Problem with the Hawkesbury as well, with the bathtub effect. If they had done releases over a week before the rain came, a lot of that would still be hanging around above the choke points now, rather than having flowed out to sea. So no guarantee that it would have made any great difference.

It's very easy to point the finger at people and say there was a better way to do things in retrospect. In retrospect there is nearly always a better way. I wonder if there will be a class action for mass compensation from the government, as there was in the Brisbane floods? I'm almost certain people will try;) Having a government minister go on the record suggesting it should have been done differently will certainly be helpful:rolleyes:


People just want to blame other people for their problems. Its just a kick arse weather system that dumped so much water the river couldn't cope. Any pre-release would have made stuff all difference to peak heights. I'd guess half a meter at best.

When i was living in Wagga in 2010, people complained that the big flood that year was all Snowy Hydro's fault, because they released some pidly amount of water to generate power the day before the flood. From memory it was something like 10,000ML/day compared to the Murrumbidgee that was flowing in excess of 300,000ML/day. On the rating curve this would have made about 5cm difference. to the flood height. But because most people can't do basic maths it was reported in the news as if there was a credible arguement against SNowy Hydro. I think it even may have featured on 4 corners or 7.30.
 

Majikthise

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Problem with the Hawkesbury as well, with the bathtub effect. If they had done releases over a week before the rain came, a lot of that would still be hanging around above the choke points now, rather than having flowed out to sea. So no guarantee that it would have made any great difference.

It's very easy to point the finger at people and say there was a better way to do things in retrospect. In retrospect there is nearly always a better way. I wonder if there will be a class action for mass compensation from the government, as there was in the Brisbane floods? I'm almost certain people will try;) Having a government minister go on the record suggesting it should have been done differently will certainly be helpful:rolleyes:
There was a bit of opinion about in early January that they could have been maintaining 85 % FSL ..
 

robbo mcs

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There was a bit of opinion about in early January that they could have been maintaining 85 % FSL ..

Yes its a reasonable argument. That would make a difference in more minor floods, but bugger all in this circumstance. Currently legislation around the water catchment specifically prohibits them from doing that though. They have been doing regular releases down to 95% in recent months, which is all they are currently allowed to do.
 

Majikthise

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Yes its a reasonable argument. That would make a difference in more minor floods, but bugger all in this circumstance. Currently legislation around the water catchment specifically prohibits them from doing that though. They have been doing regular releases down to 95% in recent months, which is all they are currently allowed to do.
Yep mandated to maintain a storage volume
 
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echidna

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Been posted ?

https://www.9news.com.au/wild-weath...rainfall/7a8fc532-bf0e-4a48-886d-b1bd0d1277bc

Warragamba Dam likely to spill for at least another week
6:48pm Mar 22, 2021

Sydney's primary water supply Warragamba Dam is likely to spill for at least another week as engineers work to control extreme amounts of rainfall hitting NSW.
Currently the volume of water spilling from the dam is 300 gigalitres per day, down from an overnight peak of 500 gigalitres a day.
For context, it's estimated Sydney Harbour in its entirety holds around 500 gigalitres.

At its peak, Warragamba Dam was spilling more than double the daily rate of water that flows over Niagara Falls.

For the past 24 hours, Warragamba has effectively been the biggest waterfall in the world based on the volume of water being spilled from its gates.


https%3A%2F%2Fprod.static9.net.au%2Ffs%2F7a24d2e0-b246-4ddc-a1c4-adea42a728d8

The Warragamba Dam was at one point releasing the equivalent of Sydney Harbour in water every day. (9News)
 

echidna

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Had a browse of https://www.infrastructure.nsw.gov.au/media/1976/taskforce-options-assessment-report-2019-v2.pdf.

Raising Warragamba's wall 14 m gives an extra 1027 GL or a 50% increase. With the current 450 GL/day dump that equates to 2.25 days extra storage for a flood this size. i.e instead of releasing from 3 pm Sat it would be starting at 9 pm tonight. Just in time to meet the Upper Nepean spills. Well they would probably alter the spill regime.
So it's only a little extra grace. Anyone for desalination expansion? Or more dams upstream / downstream -it's all there in the report.
https://www.abc.net.au/news/2021-03...dam-after-sydney-flooding-explained/100021180

There's a controversial plan for Warragamba Dam — some say it could have slowed Sydney's floods
ABC Western Sydney
Posted 2hhours ago, updated 1hhour ago

The flood emergency in Sydney's west has raised questions about whether more could have been done to alleviate the risks.

Warragamba Dam began to spill on Saturday, causing major flooding issues for Western Sydney suburbs like Penrith, as well as impacts downstream for Windsor, Richmond and surrounding areas where evacuations are taking place.

It's sparked renewed interest in a controversial plan to raise the wall of the dam by up to 17 metres.

What is the proposal?
Warragamba Dam is the main water supply for Greater Sydney and the NSW government wants to raise its wall by 14m, with 17m abutments at either end.

It would mean additional water could be held back in a large rain event, like what's currently happening. It would not be for storing more drinking water.
3b40bd960f3774d3008e0ddc3ae76ea5

Water spills from Warragamba Dam after heavy rain over the the weekend.(
Supplied:
An environmental impact statement for the project is due this year, two years later than originally planned.

It was revealed in a recent NSW Parliamentary hearing that the project could cost as much as $1.6 billion.

Would this have made any difference?
It depends on who you ask.

etc
 

davidg

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https://www.abc.net.au/news/2021-03...dam-after-sydney-flooding-explained/100021180

There's a controversial plan for Warragamba Dam — some say it could have slowed Sydney's floods
ABC Western Sydney
Posted 2hhours ago, updated 1hhour ago

The flood emergency in Sydney's west has raised questions about whether more could have been done to alleviate the risks.

Warragamba Dam began to spill on Saturday, causing major flooding issues for Western Sydney suburbs like Penrith, as well as impacts downstream for Windsor, Richmond and surrounding areas where evacuations are taking place.

It's sparked renewed interest in a controversial plan to raise the wall of the dam by up to 17 metres.

What is the proposal?
Warragamba Dam is the main water supply for Greater Sydney and the NSW government wants to raise its wall by 14m, with 17m abutments at either end.

It would mean additional water could be held back in a large rain event, like what's currently happening. It would not be for storing more drinking water.
3b40bd960f3774d3008e0ddc3ae76ea5

Water spills from Warragamba Dam after heavy rain over the the weekend.(
Supplied:
An environmental impact statement for the project is due this year, two years later than originally planned.

It was revealed in a recent NSW Parliamentary hearing that the project could cost as much as $1.6 billion.

Would this have made any difference?
It depends on who you ask.

etc
I don't see that it's necessary. Add more desal run it off renewables and drop the max level to 85% of FSL. It would be cheaper and scalable.
 

Majikthise

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Which choke point is triggered is indicative of what the cumulative streamflows are . Sackville > Castlereagh and Wallacia suggests Grose and South creek are significant. I wonder how much the urbanisation of the south creek catchment has contributed ?
 

Majikthise

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I don't see that it's necessary. Add more desal run it off renewables and drop the max level to 85% of FSL. It would be cheaper and scalable.
And as Gerg suggests modernise the gates to achieve that. The mitigation benefit is also achievable in months not years.
 
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davidg

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And as Gerg suggests modernise the gates to achieve that. The mitigation benefit is also achievable in months not years.
I want to see the Kurnell desal run off electricity from the 50MW hydro plant in Warragamba dam. Not because it makes any sense but it would be an interesting paradox. Releasing water from the dam into the ocean to generate water taken from the ocean which is then pumped back into the same network. Its like a small scale, man made hydrological cycle.
 

sbm_

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At its peak, Warragamba Dam was spilling more than double the daily rate of water that flows over Niagara Falls.

For the past 24 hours, Warragamba has effectively been the biggest waterfall in the world based on the volume of water being spilled from its gates.

The first statement was unbelievable to me and I was certain it was bullshit.

But I did the maths, 450GL a day is 5.2ML a second, with 1000L to a cubic meter, that's 5200 cubic meters (aka cumecs) a second.

Niagara Falls apparently averages 2500 cumecs. So it's right! Phaaark me.

The second statement, depending on how you define waterfall, e.g. Inga Falls on the Congo is 42,000 cumecs so a fair bit short of that.
 
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