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.
True true. So which region do you think it should cover? Open to suggestions at this point.
I'm probably the last person to ask as totally outside any area of knowledge of mine (beyond what used to be taught in schools middle of last century....). I do enjoy the discussions though from quite a few of the obviously very knowledgeable people here .
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.
I agree the water situation discussed in the SEQ NE NSW thread needed another topic.
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
Ahh yes, that topic surely wouldn’t stir up any lively debate haha
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.
Yeah, nah. Political discussion posts will deleted.
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?
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.
Warragamba could operate at a lower FSL which is a much better strategy than short term pre releaseWarrie, 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.
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.
Yep. Know it all too well. I am one those that makes such decisions (not in NSW).
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.
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
There was a bit of opinion about in early January that they could have been maintaining 85 % FSL ..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
Dammed if they do dammed if they don't
https://www.abc.net.au/news/2021-03...dam-after-sydney-flooding-explained/100021180
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.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.
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
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.
