What causes erosion on farm roads and tracks?

• Removal of protective vegetation and topsoil.
• Traffic effects: rutting, compaction, pulverising the track surface.
• High run off from the track which is filled with sediment.
• Soil erosion of track surface and drains.

Why worry about track erosion?

• Track erosion threatens your assets – its better to protect your investment; the cost of construction for a properly made track is between $5000 and $25,000 per kilometre which is much less than the value of your land, waterways and home.
• It costs more to repair a track than it does to construct it properly in the first place.
• It is important to think ahead and ensure your track can provide emergency services access.
• Well planned and constructed tracks reduce off-site impacts, which is particularly important for water quality and stream condition.

Learning more about roads and tracks:

On 4th December 2020, we held a Roads and Tracks Field Day to help track-owners understand more about creating tracks that withstand erosion.  Click on the photo below to go through a gallery of images from the day.  We were fortunate to have Peter Fogarty and Ashley Bolton sharing their expertise as we walked around a propery owned by Icon Water. You will notice that we spent a lot of time looking at our feet – or rather the track, soil, slope, runoff and erosion threats.

Some of the key points from the field day and webinar worth highlighting:

• Track surface generates runoff even after light rain.
• Bare track surfaces have high erosion potential.
• Traffic breaks up track surface into easily eroded particles.
• Sediment enriched runoff connects directly and indirectly to watercourses.
• You can’t avoid erosion – but good planning and construction can minimise impacts.
• When designing tracks keep the area of disturbance to a minimum.
• Effective route planning that takes into account topography and hydrology will enable you to avoid difficult situations.
• Track drainage is the key, as when planned correctly it minimises erosion and sediment export to watercourses.

The importance of topsoil

Topsoil is the upper layer, generally the top 15cm of soil, and it is highly important for mitigating erosion. As shown in the image, a natural, untouched layer of topsoil has a high rate of water infiltration and storage, making runoff and erosion rare. The layers further down, however, have a much lower rate of permeability and water storage, making runoff and erosion more common after rainfall events.

This explains why erosion is often high on roads and tracks on farms, as they are made by removing ,and often bulldozing the topsoil out of the way.

1. Planning

It is important to establish the purpose of the track and the volume and type of traffic that will be using the track.

A site and topographic assessment of the area around the track that looks at soil erosion hazards, landform issues, steep slopes, drainage line crossings, vegetation types and soil types.

Topographic and soil landscape maps are useful for this assessment are available in NSW and ACT.

The most important aspect to plan is the route of the track.

The grade and soil type impacts where the route can pass through.

2. Erosion control practices

This involves track surface drainage, relief drainage and drainage line crossings. Each erosion control practice will be different for each site.

3. Equipment requirements

• Construction – two types of bulldozer blades can be used; trail or straight. Trail blades can be angled and have more flexibility for casting aside windrow material. Backhoes are also used for construction of bridging and pipes or for excavation.
• Maintenance – graders can be used to clean out table and mitre drains, whilst bulldozers can be used to grade the track surface and to remove washouts and rilling.

4. Construction techniques

There are many construction techniques used, these generally include road batters, clearing the track, construcuting the track surface and constructing cross banks.

5. Maintenance

Maintenance of the tracks include inspecting after high volumes of traffic or large rainfall events, keeping roads well-crowned, checking ad removing debris from drainage system, and others that are mentioned in more detail in the webinar.

6. Revegetation

Revegetation can keep the topsoil intact on the area around the road, and reduce the speed of runoff and erosion into waterways.

For further information, please refer to the Roads and Tracks Webinar (above) and the NSW Rural Fire Service (2017) Fire Trail Design, Construction and Maintenance Manual.

Building diversion banks

Good track drainage is the key to keeping erosion of the track surface to a minimum. The most practical  and widely used (and often abused) measure to control track drainage is a rollover bank (sometimes called a diversion bank or wooboy). This video concisely shows the principles and practice of effective rollover bank construction. It will be of great interest to land managers, contractors and landholders.

The video is a collaboration between NSW Soil Knowledge Network and Soil Conservation Service, with assistance from Upper Murrumbidgee Waterwatch, Rivers of Carbon and Icon Water.

All images directly supplied by or reproduced by Rivers of Carbon, with permissions from the copyright owner(s), unless stated otherwise.