Gully system split into two to slow water flow

THE Glen Bowen site was selected as the LDC project’s second major gully remediation project in the Bowen Broken Bogie (BBB) catchment.

Dubbed “Gully 1”, it had an actively eroding footprint of about 3.36ha. The perimeter was about 1.1km and the banks of the gully scarp were, on average, 2 – 2.5m high.

Treatment

Treatment included reshaping the complex gully network into two stabilised free-draining basins by battering banks and reshaping land features using cut and fill techniques and compaction earthworks.

Three smaller gullies and six scalded areas were reshaped and compacted to protect the works.

Two rock cut-off walls were also constructed downstream of the reshaping works as well as rock check dams along the contours at one metre intervals in the basins, and in the reshaped, incised linear gullies.

As added protection to the site, the existing earth bund wall around the head of the gully was reinstated where necessary, and reinforced to manage any overland flow.

Gypsum was added to the soil in all of the works undertaken at the project site to aid the stabilisation.

Results

Gully remediation was carried out in 2019 so there has only been one wet season of monitoring post treatment.

Early indicators are positive, showing rehabilitation on the treatment gully is working effectively. 

This is evidenced by improved vegetation and biomass cover. 

Runoff samples were triggered on the control gully and not the treatment gully. This is a good sign that the treatments applied are capturing the rain that is falling on the treatment and also shows that almost no water and no sediment left the treatment gully during the 2019-2020 wet season. 

The LDC project will continue to monitor this site. In the short-term improvements in vegetation, cover and biomass, and soil condition, and reductions in erosion and gully retreat rates are expected.

In the long term, improvements in runoff and sediment loads are expected.

Data collected on the adoption and effectiveness of landscape remediation techniques and farm management practices is used in the annual Reef Water quality Protection Plan report card as well as to enhance the catchment models. 

This is facilitated through the Paddock to Reef integrated monitoring, modelling and reporting program.

*Information sourced from the CSIRO report.