I will probably be told this is Acacia longifolia but if that's the case there is a different Acacia longifolia on Isaacs Ridge as well, with different inflorescence, leaves and flowering time.
It certainly looks very like Acacia longifolia. Here are the diagnostics. http://worldwidewattle.com/imagegallery/image.php?p=0&l=l&id=17464&o=1 4-merous refers to the number of petals in individual tiny flowers. I use a x 20 microscope when looking at that feature. A hand lens is not powerful enough to see it.
You will see why I get confused if you look at http://canberranaturemap.org/Community/Sightings/Details/1945870 and http://canberranaturemap.org/Community/Sightings/Details/1944413 but NSW PlantNet shows there can be quite a bit of leaf variation. At least it keeps my brain exercised.
A site visit on 23 Sep 2017 confirmed Acacia floribunda. Many small specimens were noted over a wide area, with the obvious sources being large trees in nearby gardens and from a laneway leading from Kaepel Place onto the reserve.