To meet water quality guidelines for coastal waters of the Great Barrier Reef lagoon river sediment reduction targets have been proposed. There are more than 80,000 kilometres of gullies in GBR catchments, supplying more than 40 percent of sediment from much less than 1% of land area. This makes them a hotspot worth targeting, and means they can potentially be treated without requiring large changes in broad-scale land management. Stream banks nearby to gullies can also erode at large unit rates.
We analysed prior modelling of catchment sediment budgets to identify priority catchments that contribute large amounts of fine sediment from gully erosion per hectare. We set up a framework to assess the cost-effectiveness of erosion control actions at site scale. To avoid over-investment, more intensive and costly remediation actions such as engineered drop structures should be targeted to sites with rapid erosion, where they are required and can be cost-effective. Natural regeneration should be encouraged wherever feasible. A framework for monitoring vegetation responses was designed to check that practices were successful. This approach has underpinned two Reef Trust programs to remediate gully and stream bank erosion in reef catchments.
The approach has been applied on more than 60 large grazing properties over the past 2 years. Preliminary results indicate that considering cost-effectiveness helps to refine remediation design, with a range of techniques being applied in response to site erosion assessments. Site selection is assisted by accurate gully mapping. The degree to which site selection has been optimised is not clear, but some early indicators for increasing the likelihood of cost-effective erosion control are emerging. Engaging land holders requires win-win outcomes. Not all check dam structures have been successful, but vegetation responses are already significant at some sites. Recent research on gully erosion processes is helping to guide future activities.