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My wife's younger brother is a geologist. A few years ago, I asked him whether a seawall, or two, at certain points on the Western beach of Moreton Island would alleviate some severe erosion problems in these areas.Quote:
Originally Posted by NavyDiver
He gave the response, "You'd just be robbing Peter, to pay Paul".
'Nuff said, for me.
A typical beach is not static - it might look that way, but in most cases if you have coastal erosion on a beach, it usually means that something has interrupted the supply of sand, and often this is a seawall or other coastal structure a bit along the coast in the direction the longshore drift is coming from.
I have not seen any firm evidence for it, but I suspect that a lot of coastal erosion on the Eastern SA and western Victorian beaches results from the reduction in quantity of sediment reaching the sea from the Murray-Darling system as a result of the dams and weirs upstream and reduction in river flow as water is diverted for agriculture.
A groin was built to protect the mouth of the Tweed, then at great expense, a sand pump was built to move sand under the river to maintain the sand islands further north.
I wonder if the artificial transference of sand for the last twenty-five years has contributed to the break through of Bribie.
Nothing to do with the hundreds of thousands of cubic metres of sand removed from the Moreton Bay area for the international airport, Port of Brisbane and other projects.Quote:
Originally Posted by V8Ian
Now, I'm aware that Moreton Bay sand is replenished by Northern NSW sand, but at what rate?
Dig a hole in sand, it invariably collapses.
There's still two hopper dredges working around the clock, off Bribie, for Port extensions.
I'm not sure the sand was removed "for the international airport or for any other projects - I think it was removed from the bay to deepen and maintain the channels, and these were a convenient place to put it where it would not get washed back into the channels. Withoout these projects I suspect it was mostly taken out to deep water and dumped in what are shown on the mas as "spoil grounds".
I am.Quote:
Originally Posted by JDNSW
- Original Airport Construction (1980s):
14 million cubic meters of sand were used to stabilize the swampy land for the new airport site, according to Brisbane Airport. [COLOR=#1F1F1F !important]
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- New Parallel Runway (2010s):
An additional 11 million cubic meters of sand were dredged from Moreton Bay to create a stable base for the second runway, as reported by Moreton Bay Foundation and This Is Construction.
Way back, the original dredging spoil for the old Brisbane river port was used to form Mud Island.
My point was not that the sand was not dredged from the bay, but that it would have been dredged anyway, without the airport, although possibly not as rapidly. And the effects of this dredging on sand movement possibly relate not so much to the actual removal of the sand, as the effect on currents - for example, did the deepening of channels result in tidal currents being concentrated in the now deeper channels, effectively carrying the sand from the Brisbane river further out to sea.
Both the airport and Port of Brisbane have been pushed multiple kilometres into Moreton Bay, with sand dredged from the bay.
To think, Melburnians were up in arms over the deepening of the shipping channel in Port Phillip Bay. It was going to be the end of all life as we know it. Sure, it upset the mussel fishing mob, but they seem to have survived, if you like that sort of thing.