A "whopping great hole" is not an acceptable option for the Hazelwood mine void but a lake was a reasonable outcome, an RMIT engineering expert says.
RMIT associate professor of environmental engineering Gavin Mudd said a dry scenario for the mine void could be a "perpetual bushfire risk".
His comments come after Latrobe City councillors voted to advocate retaining a section of the mine for future coal-winning with the remainder to be made available for other uses.
Hazelwood mine owner ENGIE has stuck by plans to turn the mine into a full pit lake, citing safety concerns with a dry scenario.
"All the side walls need to be covered, physical stability needs to be assessed, water quality is a concern and how does that evolve over time ... movement in the base of the bit, which we've had in the past ... those sorts of things need to be carefully assessed," Dr Mudd said.
"I think a lake is the best outcome. Though, how high does the lake level get to? How high do we want the lake level to get to? They are not necessarily the same thing.
"This needs careful assessment, it's not a one-week engineering study, [there is] a lot of work and a lot of complex modelling."
Dr Mudd said establishing a park, as advocated by proponents of the Great Latrobe Park, in the Hazelwood mine void was possible, however, he was not convinced council's hopes to one day see the void being mined again were realistic.
"The reality is when you are looking at the future of electricity, brown coal isn't in the mix," he said.
"[A park] is possible. You have to look at physical stability especially. Growing trees, you've only got two or three metres of soil and then you're going into coal.
"Especially, if you have a bit of a storm that can come through, there is a flooding risk with the tree roots going through the soil.
"It is a possible scenario, but I think a lake is a better scenario."
Even with a lake, Dr Mudd said there were many things that needed to be considered.
"We live in a dry climate. Evaporation rates typically always exceed our rainfall rates, always a drying out force on climate," he said.
"Germany were able to make big lakes after mining, they can do that because ... they stay fresh with the influx of rainfall and run off.
"That is not the case here, things are drying out all the time and eventually you'll get a salt build-up unless there are processes mitigating that.
"China uses floating solar panels on lakes. Whether that is a good option is debateable. There are pros and cons."