seaplane_silly

On top of what Airboss777 has said, Wikipedia is your friend when it comes to researching these sort of things. But in reality Tullamarine is already Melbourne's Badgerys Creek having replaced Essendon in the 1970s. 

When you compare Sydney's Kingsford Smith Intl and Melbourne's Essendon you'll notice they're both about the same distance from their respective CBDs but unlike Sydney where they were fortunate to be bounded by 3 different waterways and able to extend runways out into Botany Bay, Melbourne was soon surrounded by houses and suburban sprawl hindering expansion to accomodate bigger jets. In fact the search for a new Melbourne airport began in the 1950s and not long after the government acquired the land for Tullamarine which was then considered rural. 

Similarly a second Sydney Airport was first proposed by the government in the 1960s and the land acquired for Badgerys Creek during the 1980s and fun fact the proposal for BC was part of the Sydney Olympic Bid - https://www.youtube....h?v=Sp2-WP5I5IA.