Targeting the right gullies. Achieving the targets

Andrew Brooks

Current estimates are that ~50% of the fine sediment load entering the GBR lagoon is sourced from gully erosion. In 2015, prior to the establishment of the NESP TWQ Program, there was little understanding of which gullies were the dominant sediment sources, how they should be remediated, what sort of sediment reductions could be achieved, how long it would take to achieve such reductions, and at what cost?

Research implemented through NESP between 2016 and 2020 addressed each of these issues, and we can report that most of these knowledge gaps have been largely resolved.

Key results:

  • High resolution gully mapping shows us that in key gully hotspot areas, 30% of the fine sediment load is sourced from between 2–4.5% of the gully population. This now provides the means to identify which individual gullies should be targeted for remediation.
  • Lifetime gully volumes derived from this mapping indicate that 156Mt (0.28 Sydharbs) were eroded from gullies over the last 130 years in the ~5300km2 mapped.
  • It has been demonstrated that large scale (i.e. sites > ~1ha) remediation of alluvial gullies can achieve >95% sediment reductions in 1 – 2 years.

This research demonstrates that the ambitious Reef2050 water quality targets are now achievable, at substantially less cost than the previous estimate of $8Bn. However, substantial coordination and upscaling of effort is required to meet the targets.