Diversion banks stop erosion, increase infiltration

Diversion banks constructed above the head of a gully has halted the progress of the gully head. Water is now being held in the landscape by the banks, instead of running into the gully system improving water infiltration.

Rehydrating landscapes is about making use of what little water there is, and reinstating the hydrological processes to return landscapes to as close as possible to their original state. This means filling the sponge (storing water) under the bit of country that is being reinstated. 

Landscape rehydration works include (but are not limited to) activities such as:

  • Leaky weirs.
  • Embankments.
  • Rock ramps.
  • Contour banks.
  • Watercourse plantings.

When complemented by a controlled grazing management plan, the outcomes can include eroded areas being restored, improved ecological health, improved water quality and increased productive capacity of the grazing landscape.

 This case study shows how Dartmoor Station, near Collinsville, is rehydrating the landscape to build resilience and improve productivity. The Mulloon Institute designed cost-effective works to stop an actively eroding gully head encroaching onto productive grazing land.  

Grazing Naturally has provided advice and oversight of the implementation of a rotational grazing plan that combines observing the environment and responding appropriately with livestock management.

DARTMOOR STATION

Problem: 

A gully head was encroaching onto productive grazing land.

Solution:

A series of rehydration banks, each about 200 metres long, were constructed above the head of a gully. The aim was to halt the progress of the gully head.

Water is now being held in the landscape by the banks instead of running into the gully system, improving water infiltration. The area was seeded with native grasses (in 2021) prior to the wet season.

Early indications are positive. Water is being held in the landscape following the wet season. A complementary grazing management plan has been implemented to improve ground cover and soil health.

Total fine sediment reduction from the treated site on Dartmoor was 16t/y. 

This was complemented by minor works on another part of the property that included the construction of diversion banks, ripping and soil amelioration that has resulted in a fine sediment reduction of 27t/y

 

Reef regulations - grazing, standard conditions

  1. For land in good or fair condition (more than 50 per cent ground cover at 30 September), continue using measures to maintain land condition.
  2. For land in poor condition (less than 50 per cent ground cover at 30 September), steps must be taken to improve land condition.
  3. For land in degraded condition (less than 20 per cent ground cover at 30 September), steps must be taken to improve land condition OR prevent areas from further degrading or expanding.
  4. Keep records of measures taken and also of agricultural chemicals, fertiliser and mill mud or mill ash applied to land.
KEQ #8

KEQ #7
KEQ #6

KEQ #5

KEQ #4

The LDC project monitors four gully sites (represented in this table) with gold standard equipment and analysis, carried out by CSIRO.

Results have been compiled in a preliminary report from Bartley et al (2020), with the final report expected to be released by the end of 2020. The preliminary report shows all four sites have indicators of improvements, notably the Strathbogie and Mt Wickham sites.

KEQ #3

*The Exploring New Incentives activity area has provided an opportunity for graziers to adopt improved land management practices through a range of activities. For some of these properties, it was the first time they signed contracts for on-ground works.

KEQ #1

Figure 1. Total fine sediment reduction by project type and erosion source. Inset shows the proportion of the total project area for each project type.

These estimates have been calculated using two methods: 

1) The pollutant reduction component of the Alluvium/Great Barrier Reef Foundation (GBRF) investment tool for hillslope and streambank erosion management projects; 

2) The Reef Trust Gully Toolbox method for gully erosion management projects. The LDC Water Quality Report 2020 (Waterhouse et al., 2020) highlights that a number of assumptions underlay these calculations, therefore these figures should be treated as the best available estimate of sediment reductions to date.

Preventing sediment from reaching the Great Barrier Reef

Each wet season sediment is washed into local waterways and out to the Great Barrier Reef (GBR). 

Most sediment is very fine, and can stay suspended for a long time and can travel great distances. Valuable topsoil is lost from production, and increased concentrations on the reef can be harmful to seagrasses and corals. 

Landholders in the BBB have completed 69 on-ground water quality practice changes, and it is estimated that these have contributed a fine sediment reduction of 6,154 tonnes per year from reaching the GBR. 

Of this, approximately half of the sediment savings are attributable to grazing land management changes on hillslopes and streambanks, and the other half as a result of gully remediation treatments across a broad range of scales, as shown in the graphs above. 

The table below also highlights the relatively small area of intervention in the gully management projects compared to the large sediment savings that these can achieve - 60 per cent of the sediment savings over only 4 per cent of the project area.

Table 1. Estimated sediment reductions (tonnes) from projects completed in the LDC Project to date.

KEQ #2

*GLMWW = Grazing Land Management Wire and Water

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