I only been to ocean beach once, so do not know the area or situation well. But its begs the question what proportion of the rubbish is dumped by people staying overnight, compared with people just visiting for the day? Often campers are given the blame, but in reality day users are just as guilty if not more so.
Down here in Marlborough DOC has done a similar thing and have restricted access to only a small part of the coast. So far they have failed to provide any reasonable explanations on why it was done. You guys are fortunate that the Council/Iwi seems interested in at least consulting.