More than 4600t of sediment loss every year stopped by remediation work
The gullies, which have been reshaped, rock chutes installed, and revegetated, were until repair, sending an estimated 4617 tonnes of sediment downstream every year.
Until the repair works, they had been expanding at an accelerated rate.
The work was designed and constructed by Neilly Group Engineering.
Works included:
- cut-to-fill reshaping earthworks to locations that were actively undergoing alluvial gullying;
- constructing grade control rock chutes to prevent the headward growth of linear gullying;
Quick facts:
- 259,703m2 footprint
- 13,536t of rock and gravel (this includes road sheeting)
- 88,866m3 of material excavated
- 86,903m3 of fill
- 4,062m3 of mill mud
- 1.8t of grass seed
- 1,232 bales of hay
- 2.8t fertiliser
- 612t of gypsum
- constructing overland flow diversion bunds to direct flows contributing to headward migration of gullies, instead over the armoured rock chutes;
- constructing porous rock check dams to slow down flows through the gully network, leading to a system with hydraulic conditions that’s more depositional and less erosive;
- ameliorating soils to treat soil chemistry (based on soil sampling) that was contributing to erosion and gullying (due to processes such as dispersion and slaking and due to poor soil nutrients limiting vegetation cover); and
- revegetating the reshaped alluvial gullies and all areas disturbed during the repair works to provide healthy levels of ground cover to ensure the former gullies are resilient to erosion.
Following remediation, observations show:
- improvements in vegetation, cover and biomass, and soil condition;
- reductions in erosion and gully retreat rates; and
- improvement in water quality (sediment concentrations) because more sediment is not being mobilised or released in the first place.
Longer term, improvements are expected to include reduced runoff and sediment loads, however this is also influenced by rainfall, so trends will take longer to detect.
The site will be monitored to measure remediation effectiveness. Initial monitoring shows some minor interventions are needed on some sections of the site. Read more about it here.
The overall aim of this remedial work was to determine the control measures capable of permanently reducing alluvial gully erosion and associated sediment and particulate nutrient export.
This project is part of the Landholders Driving Change Program funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.
