What sort of output would these proposals produce?
There's some complexity in that one......
At present there's Guthega power station (66MW) then downstream of that is Murray 1 (950MW) and Murray 2 (550MW).
Now what the issue is, is that Guthega has essentially no storage, it's a small pond that when full stores 0.53% of annual flow or in other words 2 days' worth. Bearing in mind that's 2 days' worth at average output - at maximum generation it's just 13.5 hours and that's it, no more without flow down the river.
Since most precipitation falls as snow, that leads to a situation where most generation is in spring when it melts. Average % of generation by month since 2001 is as follows:
January = 3.6%
February = 2.9%
March = 3.0%
April = 4.0%
May = 6.1%
June = 6.6%
July = 5.5%
August = 7.4%
September 17.7%
October = 22.5%
November = 14.1%
December = 7.4%
Doesn't quite add to 100% due to rounding.
With two problems, first simply being drought risk. A lack of storage means it's highly dependent on weather and that has a somewhat nasty correlation with wind. Eg 2024 was a bad year for wind generation during the second half of Autumn and first half of winter. It was also a bad time for rain, output from Guthega throughout the April to July period.
Second is simply that it's only the April to July period that's useful for firming wind and solar, that's when the problem arises that hydro (or gas) is needed to resolve. So most of the present generation from Guthega is simply useless in that regard. It displaces coal / gas and it works as peaking plant but it's no good for firming wind and solar.
Now this isn't just about 66MW, it's far more than that.
First because the new stations required to implement this themselves add another 100MW capable of constant operation (on an intermittent basis) when required to firm VRE. They're using the same water, just exploiting the head above and below the present station as well as providing the pumping function.
Second, and this is the key reason, because the ability to move water from bulk storage (Lake Eucumbene) to the Murray 1 (and then reused at Murray 2) station is only sufficient to enable a bit under 10 hours' per day running. That's fine as peaking plant to support coal, but not so good as deep firming plant to support wind and solar through a period, days, of poor yield when sustained operation is required.
Now additional to water transferred from Lake Eucumbene is water released from Guthega. Ah ha, see where this goes.....
If Guthega can be held at constant maximum release then that raises the operating hours at Murray 1 from 9.7 hours per day to 12.5 hours per day.
So in total, storing more water above Guthega enables:
Constant operation, for up to 10 days (24 hours / day) of the existing 66MW Guthega station.
Constant operation of two new small stations total 100MW.
Increase the daily operation of 1500MW at Murray 1 & 2 by 2.8 hours.
That isn't perfect of course, but there's a second stage to address that:
I haven't gone into such detail but in short it's another new dam and a new 190MW power station (with pumping) directly above Geehi pondage, which is the feed pond for Murray 1.
What this does, apart from generating 190MW itself, is in conjunction with operating the Jindabyne pumps (existing), plus the new storage above Guthega as above, provides additional storage to enable Murray 1 & 2 to operate constantly at full capacity for a full three day period, using the water released from this second new storage and power station.
So both schemes are aimed at increasing the operability of the existing large (1500MW) capacity at Murray 1&2, that's a common objective of both.
First one enables increased operation for 10 days straight but still not at constant full capacity. It also provides another 166MW constantly for that 10 days.
Second one provides 190MW for three days, plus the water to enable constant unrestricted operation of Murray 1 & 2.
Noting that both schemes are refillable either by pumping or by natural rainfall / snowmelt. Eg when the wind and sun returns, they can be refilled rapidly by maintaining the tunnel flow from bulk storage at Lake Eucumbene and pumping that up into the new storages. Or if that isn't required then they can be left to fill naturally.
Noting the new stations can of course also be used as a regular pumped storage facility for daily peaking operation, without releasing any water downstream. That isn't their primary purpose but can certainly be done, and would be done eg hot summer evenings, they can be used for that too.
Overall this isn't about more water, it doesn't add a single drop of extra water in total and the water released via Murray 1 and 2 continues to go down the Murray River and ends up in the Hume reservoir just as it does now. What it does though, is enables a shift in when generation takes place, pushing more to the April - July period to firm VRE at the expense of less during the rest of the year, especially spring.
Does that affect agriculture? Not really no, because the large storage at Hume downstream re-regulates the flow anyway. It would lead to some more variation in the water level at Hume, but given it's a completely man-made (by a dam) storage, it's not as though it's some pristine natural environment where varying the water level might stuff it up. It's a reservoir.
Overall there are many such opportunities involving the repurposing of existing hydro, to intentionally concentrate production into the times when wind and solar yields are low.
Another I've mentioned previously being the existing Kiewa stations in Victoria, total capacity of which is 397MW. There's an opportunity to raise that to about 430MW, turn it into a pumped storage scheme, and have 2.5 year's worth of water stored up the top in reserve. The idea being it would normally operate as pumped storage only, then release water "in anger" when wind and solar fall short.
Plenty more, those are just examples but they all take the basic form of storing a substantial volume of water that's held in reserve specifically to fill major gaps in wind and solar. Plus with the ability to run the hydro scheme as a pumped storage facility, without releasing water downstream, on a day to day basis so it's dual purpose.
In term of land area, it's about 0.15% of Alpine National Park (Vic) and about 0.1% of Kosciuszko (NSW) that would be submerged beneath newly created water storages. Plus some smaller disturbance for access roads, power stations etc.
So technically it's possible.
Whether it ought be done is a value judgement. Value of the hydro-electricity versus value of the National Park in its present state. That's not an engineering question, it's not something that can be objectively measured and calculated, but rather it's a value judgement as to the importance of one thing versus another.
In saying that however, the alternatives also have an environmental impact. It's not a dam versus nothing but rather, it's a dam versus gas. That's what any debate is about.
I can't speak for them but suffice to say I doubt AGL or Snowy are keen to start a war there. At present gas or diesel are the path of least political resistance.