Short Virtual Presentation & Digital Poster 10th Australian Stream Management Conference 2021

Commercial sand extraction accelerates the recovery of sand bed stream impacted by a sediment pulse (#61)

Alex Sims 1 , Ian Rutherfurd 2
  1. Alluvium Consulting Australia, Cremorne, VIC, Australia
  2. School of Geography, The University of Melbourne, Parkville, VIC, Australia

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.

Download Full Paper