These activities interfere with the natural sediment flows either through dam construction ( thereby reducing riverine sediment sources ) or construction of littoral barriers such as jetties, or by deepening of inlets; thus preventing longshore transport of sediment.
12.
Hmm, perhaps also interesting to note that Fraser Island, the world's biggest sand island ( mentioned in the OP's question ) is not far south of the main body of the GBR, although that article states " All of the sand, which originated in the Hawkesbury, Hunter and Clarence River catchments in New South Wales has been transported north by longshore transport ", which I guess rather relates back to my original reasoning to do with erosion of the soils and rocks of the continent itself, rather than it originating from the reefs.
