The beach is between Gruissan "plage des chalets" and Port la nouvelle
Just here :
http://maps.google.fr/?ie=UTF8&om=1&...,0.003449&z=18
But you have to take this way from Gruissan "village" to go :
http://maps.google.fr/?ie=UTF8&om=1&...,0.003449&z=18
You dont need a 4X4 but be carrefull, off road.
Or in pict :