Gippsland floods

 
  DirtyBallast Chief Commissioner

Location: Standing at the limit of an endless ocean
Floods in this region are not uncommon and can be expected most years at a minor level. What is currently being experienced is certainly more significant than what occurs normally, but is still not anything out of the ordinary. Not a 1-in-100 year event.

Moving the focus away from Traralgon, I'm worried about the news I'll wake up to tomorrow. Back in 2007, thanks to massive rainfall in the Macalister catchment which had yet to recover from the previous summer's bushfires, much of the valley both upstream and downstream of Licola was absolutely devastated by a huge amount of water. Debris was found in trees 11m above Cheynes bridge between Glenmaggie and Licola! As a result, further downstream, monitoring equipment was knocked out and Glenmaggie reservoir went from 50% full to massively overflowing overnight without warning. Destructive, widespread flooding occurred throughout the Macalister irrigation district after that, and even eventually affected businesses in Lakes Entrance that needed to be sandbagged.

Technically, a major flood level was also recorded at Licola this time, albeit just for a day, and the river there is now below minor flood level. But yesterday, the level in Glenmaggie was just 37.9% and today it was recorded at 71.7%. Worryingly, the river revel measured at the inflow point to the reservoir is still rising. More water is currently being let out of the weir but I fear that it is futile. The Macalister River joins the Thomson River just upstream of Sale, and the Thomson River joins the Latrobe River just downstream of Sale. The major flood levels experienced along the Thomson in that district over the past day or so have barely dropped and Sale is already experiencing moderate flood levels at its causeway. Flows are being held back by the already flooded Latrobe River. Add the potential major flood on the Macalister River downstream of Glenmaggie if the water can't be contained there, and disaster will result.

I hope I'm wrong.

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  DirtyBallast Chief Commissioner

Location: Standing at the limit of an endless ocean
Since posting the above, I have learnt that Yallourn coal mine was evacuated today because cracks were once again detected in the Morwell River levee diversion walls, which pass through the open cut mine. Specialists have been called in to assess the situation.

Info from an emergency services worker.
  BrentonGolding Chief Commissioner

Location: Maldon Junction
We copped some pretty wild weather in Central Vic this week but nowhere near as bad as you guys. And no follow up for us by the looks.

Fingers crossed it doesn't look too bad tonight. Stay safe, thinking of all Gippslanders.

Not too long ago it was drought down there. I love a sunburnt country.......
  DirtyBallast Chief Commissioner

Location: Standing at the limit of an endless ocean
Glenmaggie "only" rose another 9% overnight, so no disaster yet. One can only hope that when they do need to let 'er rip, the Thomson River will be significantly lower than what it is now so that the water in the lower Macalister can get away.

As far as the issue in Yallourn mine goes, this was published this morning:
Yallourn power station evacuates mine due to potential flooding in Victoria's Latrobe Valley - ABC News

What is not clear is if the Morwell River has once again collapsed into the mine. I suspect that the levee has been breached going by the words of Chester, but time will tell.
  Carnot Minister for Railways

Thomson Dam level has barely changed, even with 300mm in its catchment.

Btw, the new Stratford bridge appeared to pass its first flood test:
  bingley hall Minister for Railways

Location: Last train to Skaville
Apparently the Walhalla Goldfields Railway has copped a fair bit of damage which i still being assessed.
  Valvegear Oliver Bullied, CME

Location: Richmond Vic
That is not good news. If anyone has authoritative information it would be nice to know what's happened.
  speedemon08 Mary

Location: I think by now you should have figured it out
That is not good news. If anyone has authoritative information it would be nice to know what's happened.
Valvegear
One of the bridges up near Walhalla has had the abutments erode under half the bridge, if it wasnt for the piles going down to bedrock the bridge might not be standing, plus the usual fare of trees down and slight land slippage.

Speaking of which, Daylesford Railway copped a few hundred small trees down over the line, a number of them in that forest section. Puffing Billy faired suprisingly well considering, only a smallish number of trees down
  duttonbay Minister for Railways

That is not good news. If anyone has authoritative information it would be nice to know what's happened.
Valvegear
As well as Walhalla and the bridges in Stringers Gorge, the buildings at Thomson suffered, and the access road has significant damage from washaways.  Their website has a brief description: https://www.walhallarail.com.au/
  freightgate Minister for Railways

Location: Albury, New South Wales
My thoughts go out to all the families affected by the floods down in Gippsland. It looked seriously bad in the evening news.
  DirtyBallast Chief Commissioner

Location: Standing at the limit of an endless ocean
Update.

Firstly, it looks like locals have got out of jail regarding what was a very real risk regarding Glenmaggie. Several gates at the weir have been opened for a few days to reduce the level, which this morning was 84%, while ensuring that the lower Macalister did not flood. The lower Thomson is now slowly dropping, but it will take many, many days for overall riverine flood levels around Sale to dissipate. Also welcome is the latest forecast which suggests less rainfall later this week than originally thought.

Secondly, the situation at Yallourn mine is that the man made earthen aqueduct that carries Morwell River through the mine did not collapse, as it did in 2012. What happened this time was a scaled down version of what happened around the same time - the Morwell River was in flood, and tried to follow its original course. Then, a waterfall above the coal face occurred. This time, a small slip and several trickles occurred. Seems like the levee holding the original river course from entering the mine isn't quite up to scratch!
  Carnot Minister for Railways

Yallourn power plant have reduced power output and they're not out of the woods with flooding of the mine pit:
https://www.afr.com/companies/energy/flooding-hits-yallourn-coal-power-as-callide-unit-returns-20210616-p581o0
  DirtyBallast Chief Commissioner

Location: Standing at the limit of an endless ocean
Yeah. I need to correct myself with the situation at Yallourn too.

Apparently this issue is indeed with the Morwell River diversion aqueduct through the mine. Apparently it could let go at any time. This would result in a situation similar to 2012, but at least this time they can attempt to alleviate the situation by bypassing the problem area with pipework before disaster strikes.

I wonder what will happen after the power station and mine close in 2028? What will happen if it collapses in 2030? Would the mine be allowed to fill naturally (it would take decades), then when finally full, flow down the remaining channel into the Latrobe River and ultimately the Gippsland Lakes with a high degree of toxicity?
  skitz Chief Commissioner

Yeah. I need to correct myself with the situation at Yallourn too.

Apparently this issue is indeed with the Morwell River diversion aqueduct through the mine. Apparently it could let go at any time. This would result in a situation similar to 2012, but at least this time they can attempt to alleviate the situation by bypassing the problem area with pipework before disaster strikes.

I wonder what will happen after the power station and mine close in 2028? What will happen if it collapses in 2030? Would the mine be allowed to fill naturally (it would take decades), then when finally full, flow down the remaining channel into the Latrobe River and ultimately the Gippsland Lakes with a high degree of toxicity?
DirtyBallast
The area of concern is where the earth aqueduct is built on top of remnant coal.   Coal while dry holds enough friction to stay stable, hence the importance of batter water table management.   There appears to be a heave in the coal surface that has propagated into cracking through the structure.   The river normal flow is on a clay bath designed to take some movement (it moves constant I might add and is tracked as such).   Th rise of water over the clay area has entered cracks and things have moved.   So the attention is to sealing the cracks and in doing so to effect repairs will likely need some diversions of which options have not been finalized to what is next.  

Ultimately the plan for the mine when its vacated is to fill the void with water.   This will be a controlled exercise to manage water tables while the mass is replaced in the mine void, the mass of course being water.   The batters will be stable with the system in equilibrium and the water table can go back to where it does not need to be managed.

An ideal situation would to design the resulting lake to be a flood mitigating opportunity for the future.   Given the huge area it has potential to act as a massive retarding basin for both the Latrobe and Morwell rivers.   Likewise in time the Loy Yang Mine could be set up to be a retarding basin for the problematic Traralgon Creek.   Its not all bad.

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