Post #3896793

2026-07-17 12:52 UTC

I've got a question about Australian customary units of measurement. You've probably heard of very large volumes of water being measured in Sydney Harbours. For example: 'Three times the amount of water in Sydney Harbour.' My question is how much of the harbour are we including here? Like, is Middle Harbour included in a Sydney Harbour of water? What about the Lane Cove River? Are we cutting it off at Goat Island? Or Cockatoo Island? Or are we including the Parramatta River here? If so, how far up? All the salt water bits? In high tide? Or low tide? Or are including the water past the weir at Parramatta Quay? If so, are we measuring in regular conditions, or when the Parra River floods? And how far up the river are we going? Parramatta Lake is part of the same river system. Is Parra Lake included in a Sydney Harbour of water? Inquiring minds need to know... #Sydney #NSW #Australia #auspol

Replies (3)

@MsDropbear42@blahaj.zone 2026-07-17 22:27

@aj@gts.sadauskas.id.au entirely for the lucid rational reasons you list, i have long rejected this highly unreliable unit, instead favouring olympic swimming pools... but with one critical caveat... they must not have been built by the company behind the 100 metre track per The Games. i mean, c'mon, in this space the last thing we need is rigidly defined areas of doubt and uncertainty ... we're all professionals here!

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@acb@mastodon.social 2026-07-17 13:40

@aj@gts.sadauskas.id.au According to Wikipedia, a standard sydarb is approximately 562 gigalitres: https://en.wikipedia.org/wiki/List_of_non-coherent_units_of_measurement

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@Arpie4Math@mathstodon.xyz 2026-07-17 14:30

@aj@gts.sadauskas.id.au From the links in that article, we learn that the figures 500 GL (est. in the 1960's, frequently quoted) / 562 GL (high tide, 1999-2004 survey) are associated with the whole drowned valley/estuary. I have not found the original 2004 report. ——— https://web.archive.org/web/20160304091232/http://www.nswic.org.au/pdf/fact_sheets/USEFUL%20WATER%20COMPARISONS.pdf > Port Jackson, containing Sydney Harbour, is a drowned river valley and is considered a natural harbour. It is 19 km long with an area of 55 km². > One Sydney Harbour (Sydharb), (the amount of water in Sydney Harbour) is approximately 500 gigalitres or 200,000 Olympic size pools. ——— https://media.bom.gov.au/social/blog/39/when-dam-size-matters/ > Sydney Harbour holds about 500 GL. ——— https://web.archive.org/web/20160116134156/http://www.smh.com.au/news/National/The-secret-harbour-uncovered/2004/12/10/1102625541209.html > A five-year effort by the NSW Maritime Authority to measure the exact dimension of greater Sydney Harbour has revealed the estuary has nearly 80 kilometres more shoreline than anyone thought, 62,000 megalitres more water and is, on average, 1.6metres deeper. > The best estimate of the estuary's volume at high tide had been about 500,000 megalitres, but the authority now knows it is 562,000 megalitres. > Another source of confusion has been the definition of "Sydney Harbour". The estuary does not have one official name; instead, there are five formally defined parts, of which Sydney Harbour is one. All five together are sometimes called greater Sydney Harbour, while the combined parts of Sydney Harbour, North Harbour and Middle Harbour are collectively known as Port Jackson. > "Our definition of the harbour goes around every rock and every little nook and cranny," Mr Buttigieg said.

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