Hundreds of kilometres of Victorian streams have been permanently altered by sediment pulses triggered by accelerated catchment erosion. Sediment inputs have since declined, and downstream reaches have entered a recovery phase. In‑stream sediment extraction has the potential to accelerate the recovery of these degraded streams.
This study examines an 8 km reach of the Glenelg River which has previously been degraded by a sediment pulse and has been treated with managed in-stream sand extraction since 2010. Repeat cross-section surveys, extraction records and hydraulic and sediment transport modelling were used to build a decadal scale sediment budget for the reach. Channel morphology and the type and distribution of riparian and in-channel vegetation was also mapped.
In-stream extraction accelerated the recovery of the reach, but only in sections where stock had also been excluded. In reaches fenced to exclude stock, cross-section and thalweg variability was higher, in-stream vegetation more abundant and the diversity of habitat notably higher. The improvements in river condition were driven by the tendency of in-stream vegetation (Phragmites) to trap sediment and increase bed variability. In reaches with unfettered stock access, erosion lowered bed levels but did not generate a meaningful increase in channel complexity, the number and size of pools, or overall stream health.
The results of this study show that the sediment deficit caused by in-stream extraction, or other means of decreasing reach sediment supply, can accelerate the recovery of sand bed streams from a sediment pulse, but only when stock are also excluded from the channel.