Gullies that start on the steep banks of rivers and cut into terraces or elevated floodplains (alluvial gullies) can carry huge amounts of sediment out to sea and are thus a major factor affecting the water quality of the Great Barrier Reef.
Currently, there are no widely-accepted practices on how best to stabilise and rehabilitate these gullies, of which there are thousands in the GBR Catchment Area.
Griffith University’s Associate Professor Andrew Brooks is heading a NESP Tropical Water Quality Hub project to test the effectiveness of different techniques used for rehabilitating these alluvial gullies. Working with Cape York NRM, Greening Australia and the Queensland Government they are trialing a variety of methods including earthworks to reshape the gullies, and different soil stabilization strategies, such as gypsum application, mulching, rock capping, and revegetation, to dramatically reduce the sediment delivered from highly active gullies.
Initial results from the first experimental sites at Crocodile Station, near Laura in Cape York, has demonstrated that a 0.6-hectare gully system with a total erosion rate of around 260 tonnes per year has been effectively ‘turned off’ after two years. Check out this video of the works in progress.
The project’s success has prompted the Indigenous Land and Sea Corporation (ILSC), who are the owners of Crocodile Station, to expand gully remediation works on the station beyond the trial sites. With the support of the Australian Government’s Reef Trust, the ILSC has employed a crew of local Traditional Owners to undertake the remediation project, and through separate funding purchased an excavator to assist in the works.
Gullies on Strathalbyn Station, west of Bowen in the Burdekin, which have a combined treated area of 11.6 hectares (up to the 2018/19 wet season) and previously total erosion rates in the order of 3000 tons per year, have been reduced by around 90% across 1-2 years.
Rehabilitation costs for these treatments range from $400 to $2000 per ton of sediment per year depending on various factors including soil type, location and consultation.
More information about this NESP project is available online.