Channel vegetation of four small streams in southeastern Australia varies greatly in detail but it can be broadly categorised and even indexed for quantitative analysis. Such variations cause the hydraulic geometry of the study streams to differ significantly from each other and from patterns observed in most other geographical regions. Importantly, this study demonstrates that the impact of vegetation on channel form and velocity can be quantified in much the same way that other broadly based hydraulic geometry relations have been developed. Dense bank vegetation results in narrower channels whereas vegetation growing on the bed greatly increases flow resistance, causing channel widening, reduced flow velocity but no significant change in depth. The results obtained in this study, combined with those from other regions, permit an interpretation of the sensitivity of channel width to different forms of channel vegetation, information of use for river management.