If it's of any help, here are some measurements: the plants were about 20 - 30cm high and the flower heads were approx 2cm long and perhaps 2-3mm wide. Leaves were about 2mm wide.
Hi Silke. Eleocharis species are hard to differentiate. It is most likely Eleocharis acuta, which is very common around here. I have added some photos recently to help identify this species. See:- http://canberranaturemap.org/Community/Species/4716 You need to have a close look at the outer sheath, fairly close to the ground, which has a little pointy thing, called a "mucro".