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| Photo Credit - Mattinbgn/gallery 003 |
The latest figure we've been following has Eppalock at 99.06%, holding around 301.8 GL.
Full supply is about 304.65 GL, meaning there is less than 3 GL of room left.
And now the rain has arrived.
The Bureau of Meteorology has forecast 6–15 mm around Eppalock today, with a 100% chance of rain and the possibility of a thunderstorm during the afternoon.
With the lake already sitting so close to full, it won't take a massive amount of additional net inflow to get it there.
So what happens if Eppalock spills?
This is where it gets interesting for those of us further downstream.
Lake Eppalock sits on the Campaspe River. Water coming into the lake is fed by the Upper Campaspe and Coliban rivers along with McIvor and Wild Duck creeks.
Once the lake reaches full supply level, Eppalock has a fixed-crest spillway.
In simple terms, once the water gets high enough, it goes over.
Goulburn-Murray Water says it can't simply open large spillway gates to control this. Its outlet valve can release up to about 1,600 ML a day, but during a spill the amount going downstream is governed largely by how far the lake rises above full supply level.
From Eppalock, that water heads north down the Campaspe River.
It passes through the Campaspe system, past places including Barnadown, Elmore and Rochester, before continuing through the lower Campaspe.
And eventually the Campaspe joins the Murray River at Echuca.
So yes, if Eppalock spills, some of that additional water ultimately becomes part of the Murray system.
It won't suddenly create a massive rise in the Murray hundreds of kilometres downstream. There are tributaries, river operations and plenty of distance involved before that water gets anywhere near Sunraysia.
But it's another contribution.
And Eppalock isn't happening in isolation.
The Upper Murray catchments have also received substantial rain, Hume has been climbing strongly, and other Victorian storages and tributaries have been receiving useful winter and early-spring runoff.
Put all those contributions together and the Murray heads into spring in a considerably more interesting position than it appeared to be only a few weeks ago.
Will Eppalock spill today?
That's the question everyone will be watching.
At around 99% full, there simply isn't much room left.
But rainfall over the lake itself isn't the whole story. What matters is how much water comes down the Upper Campaspe, Coliban and smaller creeks and how quickly that runoff reaches Eppalock.
There can be a delay between the rain falling and the lake responding.
So while a spill today is certainly possible, it could just as easily be the runoff arriving later today or into Sunday that finally pushes it across the line.
One thing is certain:
Lake Eppalock is about as close to full as you can get without actually being there.
After watching it climb rapidly through the past few weeks, the next 24 hours could be very interesting.
