the bottom of the harbour

Yesterday I walked around the Circular Quay and Rocks area of Sydney Harbour. A bonus was a full-sized cruise ship at the Overseas Passenger Terminal. A second bonus was that I found (on the terminal’s website) that it was due to depart in 40 minutes, so I positioned myself on the footpath above Circular Quay station (where I’d been several hours before).

One of the reasons Sydney (first the settlement/town then the city/metropolitan area) is where it is, is that there is deep water right up to the shoreline – deep enough for the sailing ships of 1788 and, it turns out, for the cruise ships of the 21st century.

Some time ago I saw a ‘photo’ of Sydney Harbour without water. This morning I thought about finding it, and a quick search found this one. How scientifically accurate it is? It is on the webpage of a conference organised by the University of Sydney, so they must think it’s academically respectable, but the photo is credited as ‘sourced via Quora’. I can’t find anything by searching for ‘Sydney harbour without water Quora’. 

Things to notice are the outcrop which forms Goat Island (top right) (I would like to see Fort Denison/Pinchgut Island, but that’s just to left of this photo) and how deep Campbell’s Cove (in the side of Sydney Cove) is. 

But I have my doubts. In real life, most if not all of the Opera House sits on an artificial platform, not solid rock, and the shoreline, especially of Circular Quay, has been adapted many times along the way; for example, Cadman’s Cottage (not discernible in this photo) was once on the waterfront but is now perhaps 50 metres inland. And even without the ocean flooding the valley, the Parramatta ‘River’ would still flow through it.

A newspaper article includes maps prepared by hydrographic surveyors at Sydney Ports, but doesn’t include a scale for the colour-coding. I guess that red is the shallowest and blue is the deepest. Note the comparatively narrow channel off Bradley’s Head (centre right). 

So how deep is a cruise ship? Wikipedia reports that this particular ship has a draft (depth below the waterline) of 7.7 metres. It doesn’t say how tall it is overall or above the waterline, and neither does the ship’s own website (in fact nowhere within a reasonable search of the internet does), but it’s obviously a lot more than that. My second photo shows it’s about half the height of the tallest roof of the Opera House, which is 65 metres, so about 30-35 metres, . 


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