Technical findings and outcomes from the Reef Trust Gully Erosion Control Programme

[摘要] Gully erosion is the largest source of fine sediment and associated nutrients in the river basins draining to the Great Barrier Reef (GBR) lagoon, yet it occupies less than 1% of the land area. A synthesis of local and global literature indicated that gully erosion control could be used to reduce fine sediment loads to the Great Barrier Reef lagoon (Wilkinson et al., 2015c). The Australian Government’s Reef Trust invested approximately $8M in the Gully Erosion Control Programme (the Programme), to control and prevent further erosion in gullied areas delivering sediment to the GBR lagoon over the period from July 2015 until December 2018. This report describes the outcomes and findings of the technical partner project which supported the Programme, to provide feedback for organisations which delivered erosion control in the Programme, and to help inform future investments in gully erosion control. The technical partner was a team of researchers in gully erosion who were contracted to assist the establishment of the Program, including developing the Gully Toolbox as a technical reference for Programme implementation which included a cost-effectiveness calculator and monitoring and reporting protocols (Wilkinson et al., 2015a). The Programme was delivered by six delivery partners, who were natural resource management (NRM) agencies or companies, and the technical partner provided advice on their delivery approaches and on-ground activities, and on monitoring and reporting. To facilitate exchange of experiences and to identify progress and challenges, the technical partner convened two forums to bring together all involved in the Programme. The technical partner also analysed Programme outcomes and findings which can inform future activities. Gully erosion control was undertaken on 210 gullies and 88 properties. Based on site estimates of gully volume, age and soil properties, and of the proportional reductions in ongoing erosion rate resulting from erosion control activities, these activities are expected to deliver a reduction in fine sediment export to the Great Barrier Reef (GBR) lagoon of 5,400 t/yr, and bioavailable nitrogen and phosphorus loads by a conservatively estimated 1,600 kg/yr and 720 kg/yr, respectively. These reductions will persist for the life of the works which is expected to generally be at least 20 years. The works involved $2.8M of direct on-ground costs, leading to the load reductions averaging $510 per t/y reduction in fine sediment, or approximately $1,500 per t/y at Programme scale if all aspects of delivery such as site identification, communication and monitoring are included. The sediment savings from the Programme were 10 times those which would have been achieved without spatial targeting of active gullies at river basin and site scales. However, the load reductions achieved by this Programme are small relative to the targets which have been set. Across the 423,000 km2 of the GBR catchments there are approximately 80,000 km of gully erosion. The Programme demonstrated that cost-effective water quality improvement through gully erosion control can be used to reduce sediment and nutrient loads. It established a structured approach to implementation, which can assist further work at a larger scale. In basins where the magnitudes of target nutrient reductions are large in absolute terms and relative to baseline levels, a combined approach of both erosion control and fertiliser management should be considered. The Programme enabled significant development in the local capacity to deliver gully erosion control, and it will be important to maintain and build this capacity to assist progress towards water quality targets. (continued)

[发布机构] CSIRO

[学科分类] 地球科学(综合)