From the Wikipedia article on Small's Creek (which is mainly sourced from http://parramattariver.org.au/wp-content/uploads/Rep2429v3.pdf), it says it is sourced in Darvall Park and Outlook Park. Looking at the terrain map seems to show that to be possible too. I think at one point there used to be an unnamed creek/stream drawn through the park, and the existence of a bridge in one of the east-west walks also makes sense. That is why I am considering the possibility that perhaps Small's Creek extends North towards Eastwood through West Ryde and Darvall's Park. However I haven't gone to this area in a while which is why someone more familiar will need to verify/disprove this.