Stabilising active gully heads

Before you start

Before beginning any on-ground works:

• Assess the size, depth and slope of the gully and the strength of incoming water. Learn more about how to assess gully erosion.
• Understand the causes before intervening, read about how gully erosion forms.
• Maintain groundcover and limit further disturbance to prevent erosion from worsening.
• Before undertaking an major earthworks or engineering work, get advice from Local Land Services.

Methods for stabilising active gully heads

Early stabilisation of the gully head can help to prevent further erosion.

Battering low vertical faces 

Battering, which is flattening out the flow path, can prevent the waterfall erosion process from moving further up-slope. 

The low vertical face is battered by deep ripping across the direction of the on-coming water. 

This method is effective when: 

• the vertical face is less than 30 cm in height
• the oncoming run-off water is not particularly strong. 

Any gutters immediately below the ripping area should also be battered or flattened out. If this doesn’t occur they will start the erosion process again. 

A soft filter below the deep ripping will slow water flowing down the batter and improve the success of rehabilitation. More soft filters within the gully below the repaired gully head will speed up rehabilitation of the gully floor. 

A soft filter is a leaky barrier for flows. They are usually constructed with logs and branches, anchored with star pickets.

Armouring battered slopes 

When water flows are stronger, you can protect the battered slope with erosion-resistant materials. This process is known as armouring. You can achieve armouring by using:

• geotextile fabric
• rock or compacted calcrete.
• Vegetation material can also be used to protect small batters. The vegetation can include small logs, branches and bushes and may need anchoring with wire and steel pickets.

Battering and armouring the slope avoids diverting natural water flows. This approach can be labour intensive and expensive.

Check banks

Battering and armouring will not be successful if the gully head is deep and wide. These gully heads require carefully surveyed check banks above them. You will need to construct these with heavy earthmoving machinery.

The design and layout of check banks varies greatly and depends on the surrounding shape of the landscape.

If the fall of the slope is away from the gully, a simple check bank above the gully head will block water flows entering the gully. It will re-establish the natural flow path away from the gully. This scenario is common where a road has initiated the gully.

Where the gully is in the bottom of the watercourse, a series of check banks will need to be constructed to keep the water flows out of the gully.

A check bank at the top of the gully head will spread the water flows away from the main gully head. However, the water will tend to return into the gully by side gully heads.

To prevent this, you will need to construct a series of check banks, called champagne banks. This will keep the water flow out of the gully.

The champagne banks continue along the side of the gully until a stable re-entry point is found or an area is found where water will flow away from the problem area.

It is important to use a level to determine the direction and slope of the land before choosing a repair strategy. Surveying should take place before and after all on-ground works. 

Drop structures

In some cases, water flows cannot be spread away from gully heads using check banks or champagne banks. This occurs where the land rises sharply on both sides of the gully. 

In this situation, the water flow should be allowed to enter the gully via a drop structure which is a controlled entry point. 

A drop structure needs careful planning and construction. Professional input is recommended to improve chances of success. A drop structure is like a weir placed in a gully that ponds some water and allows the excess to flow over a central point. They vary from simple structures made with fence pickets holding wooden posts, to major structures armoured with geotextile and rocks.

Recommendations

To prevent erosion, new gullies forming and improve stabilisation success:

• Maintain groundcover and minimise disturbance when making and managing tracks or fences.
• Fix small erosion problems early before they become major issues.
• Match each repair method to the landscape and desired outcome.
• Incorporate all banks into the landscape by ripping and removing vegetation where banks will be placed.
• Do not disturb spilling areas and let the water out calmly onto a stable surface.
• Consider seeding where key plant species are missing from the surrounding landscape.

Your next steps

Seek professional advice before undertaking major gully head system stabilisation works or earthmoving.

Local Land Services can help with advice on the design, construction and required maintenance.

Learn more about erosion control:

• Erosion control
• Revegetation works