I'm thinking- more like Carex. Eleocharis spikes don't usually spread like that, and the sheathing base is not like Eleocharis that I am familiar with. Does 'tubular' also mean that the culm was hollow and/or round ?
Thanks for following this up. Yep C. tereticaulis with its terete (cylindrical) culms seems to fit as does this description in PlantNET (https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Carex~tereticaulis) indicates "...Culms erect, terete to subtrigonous, glabrous, 40–120 cm long, 2–4 mm diam. .... Differs from the related C. appressa in its terete, smooth, grey-green rather than yellow-green culms, the reduced leaves, and in the utricle, which is thickened at the base but not truncate....".
Still think this is C. tereticaulis - for example compare with sightings https://canberra.naturemapr.org/sightings/4570369, https://canberra.naturemapr.org/sightings/4540628, and https://canberra.naturemapr.org/sightings/4555195.