Gully erosion assessment guide

Inspect the gully to determine which components are stable or active. Look closely at three main components:

• Gully head: Check for undercutting, collapsing or vertical faces.
• Gully floor: Look for exposed soil, running water, or fresh sediment.
• Sidewalls: Check for cracks, slumping, or bare patches.

If the stability varies along the length of the gully, break the system into smaller sections. You can develop management options for each section, or assess only the area where you will implement erosion controls. 

Example of erosion classification class 1-2. It has an active gully head, lack of stabilising vegetation and fresh sediment deposits. 

Example of erosion classification class 7-8 with a stable gully head. It has actively growing vegetation, dense vegetation cover on a stable gully floor. 

Use the gully erosion classification system to rate each section of the gully from 1 (most active) to 8 (most stable).

Gullies with an erosion class 1 to 4 will generally need earthworks to stabilise the active gully head. 

Gully erosion classes 5 to 8 generally have a stable gully head. They need management options to deactivate either the gully walls or gully floor or both of these components. 

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Depth rating

Use the gully depth to help prioritise rehabilitation works.

Different gully classes need different management approaches. Always seek professional advice before starting earthworks.

The options depend on the source of the erosion and how the different parts of the gully are interacting with each other. Fencing off gully systems to exclude stock is recommended for all erosion class ratings.

If earthworks are recommended, seek advice on the design, construction and maintenance of such works. 

Classes 1–4 (active gullies)

• Gully head: Stabilise the gully head by diverting run-on water. This may involve simple diversion banks or more complex earthworks such as a gully control structure or flume.
• Gully walls: If sidewall erosion is caused by run-on water, use diversion banks to redirect flows. Where stock traffic contributes to erosion, fence the gully system to exclude animals and allow natural regeneration. These areas usually stabilise over time.
• Gully floor: Once the gully head is stabilised, the floor often becomes stable as well. Natural regeneration may occur, or you can revegetate to speed recovery. If erosion continues after the head is stabilised, it may be due to lateral flow or secondary head cuts. Secondary head cuts should be treated at the same time as the primary head cut. Install bed stabilisation structures such as V‑notch weirs or rock ramps, and revegetate the gully floor with suitable native species.

Classes 5–6 (moderately stable gullies)

• Gully walls: If the sidewall erosion is caused by run‑on water, use diversion banks to redirect the flow. Where stock traffic is contributing to erosion, fence the gully system to exclude stock and allow vegetation to re‑establish. These areas can stabilise naturally over time.
• Gully floor: If the gully head is already stable, the floor will usually stabilise too. Revegetation may be used to speed up recovery. If erosion continues after the head has stabilised, it may be caused by lateral flow or secondary head cuts, which should be treated at the same time as the primary head cut. Install bed stabilisation structures, such as V‑notch weirs or rock ramps, and revegetate with appropriate native species.
• Groundcover: Maintain high levels of grass cover to protect soil from runoff and erosion. (moderately stable gullies)
• Revegetate bare areas to prevent reactivation.

Classes 7–8 (stable gullies)

• Keep groundcover high and manage grazing pressure.
• Continue monitoring to prevent reactivation during high rainfall or drought periods.

Some gullies cause more damage than others. Prioritise work where erosion has the greatest impact on your property, nearby waterways and infrastructure.

On a catchment scale, larger and more active gullies usually contribute higher sediment and nutrient loads to downstream watercourses. Smaller gullies may also be a high priority if they threaten farm infrastructure such as roads, tracks, fences or watering points.

The connectivity of the gully to main waterways affects how much sediment reaches rivers or wetlands. For example, a small gully directly connected to a creek can have a greater water quality impact than a large gully further upstream that traps sediment before it reaches a watercourse.

Consider:

• Size and activity: Larger, more active gullies contribute more sediment to watercourses.
• Proximity and connectivity: Gullies linked to creeks, rivers or wetlands have greater downstream impacts.
• Infrastructure risk: Small but connected gullies near roads or fence lines may need urgent attention.

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This matrix is an example of a simple way to assess the priority of your gully, using the gully erosion class rating system mentioned in step 2.