Thought some people may enjoy this regarding the formation of Sandy pt (The Pit), some interesting aerial photos going back to the 40's.

Abstract: The sand spit that separates Shallow Inlet from Waratah Bay (38?52? S, 146?13? E), near Wilsons Promontory
in southern Victoria, has developed since the previous spit was washed out in 1901. Initially without vegetation, the
spit was colonised in the 1960s by the exotic grasses *Thinopyrum junceiforme and to a lesser extent *Ammophila
arenaria. blah blah blah

http://www.rbgsyd.nsw.gov.au/__data/assets/pdf_file/0003/81597/Cun94Hey571sm.pdf

If you can get National Parks on side, if they agree that the weeds are forming an unnatural spit, then why don't you form a volunteer landcare group and treat the weedy mounds before they link up. 3 or 4 people once a month should hold it at bay and make steady progress. Even roundup, the most environmentally sensitive herbicide, kills most things if you hit it once a month.