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Gully erosion

Since European settlement, it is estimated that nearly 325,000 km of Australian gullies have eroded about 4.4 billion tonnes of sediment into waterways.

Restoring gullies can make a difference in the:

  • home - reduced property management time
  • paddock - retaining fertile soils
  • catchment - reducing sedimentation and improving fish habitat and water quality
  • community - improving resilience.

What is gully erosion?

Gullies are open erosion channels at least 30 cm deep. They appear when concentrated, fast flowing water hits a small surface depression, such as the ruts left by farm machinery or livestock tracks. The water scours away the soil and undermines the vegetation.

Once the vegetation and topsoil are removed, gullies spread rapidly up and down drainage lines. Intensive agronomy often reduces the structural stability and fertility of the soil and can worsen the natural gullying process.

Impacts of gully erosion

On-site changes include:

  • soil loss
  • paddock dissection
  • smothered infrastructure
  • reduced property values.

Off-site changes include:

  • poor water quality
  • loss of in-stream habitat
  • damage to public amenities
  • increased transportation of nutrients with run-off.

How can I fix gully erosion?

Large active gullies can be difficult to control and can be expensive to repair. However, leaving a gully to stabilise itself can be detrimental to property management and overall catchment health.

Prevention and control

Regular property inspections are an important part of preventing gullies. Carefully check potential sites of gullying, such as stock and vehicle tracks where there is no vegetation, drainage lines, overgrazed paddocks and intermittent waterways.

The first thing to do if you find a gully is remove the pressure from grazing stock and farm vehicles. Then think about other options.

Is the gully still active?

Gully erosion can look dramatic, but if the gully has stabilised it may be best left alone. Disturbing soils that are prone to break down in water may reactivate the gully and cause more erosion.

To check if a gully is active:

  • look at the gully head, walls and floor
  • active gully heads cut into the drainage line and move back up the slope
  • gully walls tend to have vertical sides and the floor will lower over time
  • establish photo points and check for movement.

Where is the water coming from?

Gully erosion results from surface and subsurface flows. Finding where the water comes from helps you decide what rehabilitation options are best.

Which option – soft versus hard?

Gully type

Water source

Rehabilitation options

Soft: revegetation, stock exclusion fencing, etc

Hard: earthworks, construction of diversion channels, etc

Minor

Groundwater

X

 

Surface water

X

 

Severe

Groundwater

X

 

Surface water

X

X

The soft option

Adequate groundcover is vital for soil protection. As a general rule, 70% groundcover is needed to protect soil from erosion. In areas of increased flows this needs to be thicker. Consider:

  • replanting sparse areas
  • fencing out stock so young plants can establish and the gully can stabilise
  • planting deep-rooted perennial grasses in and on the gully walls
  • planting trees further away to take up groundwater.

The hard option

When erosion is severe, planting and fencing alone won’t be enough and earthworks may be needed. Earthworks can include:

  • structural works to stabilise the gully head
  • reshaping, battering and revegetation of the gully walls
  • building contour banks
  • distilling basins to control run-off.

It is important to obtain advice and permits before undertaking earthworks. For more advice, call your Local Land Services office on 1300 795 299.

Key points to remember

  • Gullies are common landscape features, especially in tablelands and upper catchments.
  • Inappropriate land use practices can set off or worsen gully erosion.
  • Removing existing pressures is the first step stopping gully erosion and reducing soil loss.
  • Carefully assess gullies to decide what rehabilitation measures are needed.
  • Good land conservation techniques will often prevent gullies.