Australian rivers frequently exhibit long periods of lowor no flow, trees and shrubs that growon the channel bed,
and discharges that decline downstream. Four channels of the Gwydir distributive fluvial system (Gwydir and
Mehi Rivers; Carole and Moomin Creeks) greatly contrast the hydraulic geometry of most other rivers,
particularly in the way they respond to changes in discharge downstream. Data describing 167 cross sections
across all four streams are assembled into standard exponential bivariate hydraulic geometry plots, with the
relationships shownto exist outside the range of previously investigated downstreamchanges (i.e., in contrast to
the commonly obtained exponents for width [b], depth [f], and velocity [m] of ~0.5, ~0.4, and ~0.1, respectively).
Comparatively low exponents for width (b=0–0.4) and high values for velocity (m=0.26–0.42) reflect the
importance of slope in accommodating changes in discharge. In sharp contrastwith nearly all previous hydraulic
geometry investigationswhere discharge increases downstreamand slope decreases, in theGwydir systemslope
declines in sympathywith discharge resulting in a marked downstreamdecline in streampower. The presence of
in-channel vegetation is also argued to be a highly significant influence on the downstreamhydraulic geometry of
these streams. Because these streams are frequently dry, trees grow in abundance on the bed, appearing to
displace the flow laterally and causing the channels to widen and shallow downstream — an adjustment that
contrasts the high mud content of the boundary. The result is a very different hydraulic geometry in this
anabranching-distributary system to that commonly described for other types of river.