The role of vegetation in the formation of anabranching channels in an ephemeral river, Northern plains, arid central Australia

摘要

As the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels, riparian vegetation has the potential to influence significantly dryland river form, process and behaviour. This paper demonstrates how a small indigenous shrub, the inland teatree (), influences the formation and maintenance of anabranching channels in a reach of the ephemeral Marshall River, Northern Plains, arid central Australia. Here, the Marshall is characterized by , where water and sediment are routed through subparallel, multiple channels of variable size which occur within a typically straight . Channels are separated by — narrow, flow-aligned, vegetated features — or by wider . By providing a substantial element of boundary roughness, dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities, flow depths and sediment transport, resulting in flow diversion, bank and floodplain erosion, and especially sediment deposition. Ridges and islands represent a continuum of forms, and their formation and development can be divided into a three-stage sequence involving teatree growth and alluvial sedimentation.This sequence turns a channel, initially obstructed with dense and chaotic stands of teatrees, into a well-organized system of ridge-form anabranches. In the moderate- to low-gradient Marshall River, which is colonized by an abundance of within-channel vegetation and subject to declining downstream discharges, this helps to minimize flow resistance, thereby maintaining an efficient water and sediment flux. Copyright © 2000 John Wiley & Sons, Ltd.