Am thinking GBC that the track you took on the bikes would be the 'Telstra track' that supplied phone to Teewah in the late 80s and then also power in about 2002. Skirts the swamps between Teewah and behind the 3rd cut - comes out at Teewah at the dump - which is now just green waste. Many here are wanting this gated track which is semi maintained to be able to be used by landowners in emergencies or when the beach is difficult - but when the beach is difficult, the swamps tend to be over the track. I often run this track and it is currently under a couple of feet of water in places and loaded with red belly blacks.
The original 'emergency' track, which was possibly cut during WW2 as there was a look out tower built on the dunes where the rocks south of Teewah are, but could also have been cut by sand miners in the 60s, was just in behind the dune proper. It entered Teewah at the north eastern end and came out where the sand mining depot was at the 3rd cut - the remnant tailings having only just in the last 2 years been removed and exported to China. We took this track after being stranded in Teewah for an extra week in '73 or '74 and it was getting overgrown then. Last walked along it in the late 80s and it was hard to find and is completely covered in mostly lantana now.
These days we have a helipad for emergencies.