Key outcomes

• • 258t of fine sediment prevented from entering local waterways.
  • Stabilised and reduced erosion.
  • Increased soil water-holding capacity.
  • Promoted perennial pasture regeneration.
  • Earthworks carried out by local contractors Colls Earthmoving.
  • The third Mulloon Institute designed landscape rehydration project for the Landholders Driving Change (LDC) project. The other two are Mt Pleasant and Dartmoor stations, also in the Bowen Broken Bogie (BBB) catchment.

Project Aims

The project aimed to demonstrate the efficacy of landscape rehydration in reducing the amount of fine sediment reaching the Great Barrier Reef while improving production outcomes for landholders.

Project Objectives

Demonstrate erosion control measures which slow, spread and infiltrate surface water flow.

Reinstate hydrological function present prior to channelisation.

Enhance primary production through improved nutrient cycling and increased soil moisture.

Improve biodiversity through improved habitat.

Rebuild landscape function and resilience.

The site

Weetalaba Station is a 20,800ha grazing cattle property 50km south of Collinsville.

The waterway flowing through the project site is unnamed and mapped as a first order stream with a catchment of 270ha at the bottom of the treatment site.

This waterway flows into Kangaroo Creek which runs through the property, and into the Bowen River.

The uppermost channels in a drainage network (that is, headwater channels with no upstream tributaries) are designated as first order streams down to their first confluence.

The erosion site was an active alluvial fan that cut a shortened path to nearby Rosella Creek. Large active black soil gullies from overland water flows were dropping into the feature.

The intervention, a series of dam walls and diversion banks, has resulted in spreading water across the landscape, increasing inundation and infiltration across the plain, increasing deposition of sediment, and slowing subsurface moisture movement.

The long-term benefits of the works will include increased water infiltration, healthier soils, more diverse pastures, increased grazing capacity, reduced erosion, and improved water quality.

A grazing management plan has been implemented to combat erosion and to improve landscape function, specifically ground cover.

Landscape rehydration techniques at Weetalaba are expected to improve productivity by slowing water movement across the landscape, promoting infiltration rates to enhance pasture growth.

Slowing water movement reduces erosion, increases pasture yields, generating economic and environmental benefits.

Interventions used natural materials to lift and spread water higher in the landscape and re-establish an older flow pattern where water used to run parallel to Rosella Creek for about six kilometres before re-entering the creek system.

The interventions spread water across the landscape, increased inundation and infiltration across the plain, increased deposition of sediments, and slowed subsurface moisture movement.

Interventions

Interventions included dam walls, diversion banks and a rock ramp.

Dam Walls

Three dam walls were built across the site to:

• • halt the progression of advancing headcuts;
  • restart depositional processes across overland flow pathways;
  • provide stock water; and
  • provide rehydration through standing water behind dam walls.

Diversion Banks

Three diversion banks were built. Banks 1 and 2 were to:

• • starve gullies of flow to reduce the movement of headcuts and sidewall erosion;
  • direct flow intact landscape features;
  • reinstate depositional processes in the landscape;
  • safely contain flow from landscape features vulnerable to erosion; and
  • act as dam spillways.

Bank 3 was to:

• • safely contain flow from landscape features vulnerable to erosion; and
  • act as an emergency spill point for dams.

Rock ramp

A rock ramp was built to armour an existing headcut at the bottom of a flowline to:

• • protect the intact flowline from incision; and
  • safely step water down from surface level to bed level.

A demonstration site, the LDC project has hosted several field visits to Weetalaba to show landholders and land managers options to manage the landscape to capture and hold rain where it falls, slow and spread water flow, intervene in active gully erosion, increase water infiltration and grow more grass.

Monitoring of the site will continue.

The BBB produces almost a quarter of the total fine sediment load that ends up in the Great Barrier Reef lagoon.

About 65 per cent of that fine sediment comes from gully erosion which makes gully management a high priority for investment.

It’s also why gully remediation is a key component of the LDC project.

The Challenge

The Burdekin catchment (map, above) is the largest contributor of anthropogenic fine sediment loads of the 35 catchments that drain to the Great Barrier Reef. It delivers, on average, 3.3 million tonnes per year; more than double the load of any other catchment.

Most comes from gully erosion in grazing areas.

The Bowen Broken and Bogie (BBB) river catchment, an area of 11,718km², is less than 3 per cent of the catchment area draining into the Great Barrier Reef.

However, it generates almost a quarter of the total fine sediment load and about 65 per cent of that comes from gully erosion. A total of 22,311 active gullies were mapped within the BBB study area (~3,500 km² ), covering a total of 4,620ha.

Gully remediation in this landscape is challenging.

The climate — a pronounced wet and dry season — allows a narrow window for undertaking earthworks and revegetation is constrained by water availability.

Characteristics vary considerably between gullies, requiring tailored treatment plans for each one.

The Response

NQ Dry Tropics is piloting a suite of landscape interventions and land management efforts at a catchment scale to improve water quality and sustainable land management in the BBB.

This includes small-scale, large-scale, and landscape rehydration interventions.
The aim is to help landholders and land managers develop cost-effective designs to reduce soil erosion.

Technical experts can work alongside landholders to design and deliver treatments, using local contractors where possible, and sharing resources to help reduce costs.
Work arising out of the LDC includes:

• • transferable procedures for remote sensed mapping and characterisation (including load estimates) of gullies;
  • an extensive, spatially-explicit, GIS dataset that identifies, characterises and prioritises active gullies in the BBB;
  • a framework for site selection incorporating biophysical and socioeconomic considerations; and
  • a spatial prioritisation based on cost effectiveness incorporating biophysical characteristics and socio-economic considerations.