Every bit counts: working on small gullies to reduce sediment

Scottville grazier Graham Gordon has undertaken small-scale gully works to slow water on his 222 ha property to improve soil and pasture health, and reduce sediment loss. 

Graham accessed technical expertise and resources to halt progress of an active gully that had two head cuts through the Landholders Driving Change project, funded through the partnership between the Australian Government's Reef Trust and the Great Barrier Reef Foundation. 

Through this project, landholders in the Bowen, Broken, Bogie catchments are developing and implementing cost-effective designs to remediate small-scale gullies to reduce soil erosion and improve water quality.  

Technical experts work alongside graziers to design and deliver treatments, using local contractors where possible, and sharing resources to help reduce costs.  

NQ Dry Tropics’ Soils Conservation Officer Bernie Claussen said Graham took advantage of the opportunity to access technical advice to help him design and deliver the most appropriate treatments. 

“Prior to this project, Graham had remediated numerous gullies using heavier earthworks and machinery,” Bernie said. 

“He was open to trying these lighter works which could be completed with his tractor and bucket, and some elbow grease. With such severe erosion, there are no quick fixes or one-size-fits-all solutions. Landholders like Graham who are adaptive, inquisitive and keen observers of the landscape are a pleasure to work with and everyone involved learns from the results together,” she said. 

Graham implemented a horseshoe-shaped level rock weir with spreading structures above the gully heads to slow and spread water, and to reduce the volume and velocity of water entering the gullies.  

The leading gully head was backfilled, forming a gentler slope to enable plants to grow, essential for stabilising the area. 

Leaky weirs were installed in both gullies to help stabilise gully floors. Rock gabions suited the deeper gully where bedrock was exposed, while more porous netting and mulch weirs were installed higher upslope where there was soil.  

The gabions are expected to collect debris and sediment, helping fill in the gully, providing further stabilisation and facilitating vegetation growth. 

All bare areas, including the side walls, were covered with a layer of mulch of 1-5 cm thick. This protective cover will reduce the erosion that occurs from raindrop impact by cushioning the blow from every raindrop falling on the fragile, slaking soil. 

An adjacent smaller gully that was cutting down to the sedimentary bedrock was treated with rock weirs to make good use of spare rock left over from the treatment works.  

The project site is located downslope of erosion mitigation work undertaken by Graham 12 months earlier. He said completing mitigation at this site was a logical next step to remediate the catchment. 

“We’re taking a whole-of-property approach to fixing gullies. Being a smaller property, means we’re able to do that,” Graham said. 

“If you can block a gully and hold that water back in the country, you’re going to keep water and soil on the paddock, and that’s a whole lot better than seeing it run into the creek. It’ll improve our topsoil depth and soil-water-holding capacity to enable even grazing of our pastures,” he said.