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Tunnel Erosion
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Tunnel Erosion


Tunnel erosion commonly occurs on slopes that have subsoil easily dispersed by water and a surface soil that is much less erodable due to its inherent structure, chemical composition or the presence of plant roots. As the subsoil begins to wash out, tunnels form under the more stable surface soil and extend up the slope, increasing in size after each bout of heavy rain. If the tunnels become large the surface soils may collapse forming a small gully.


Hidden tunnels are dangerous to stock and for people on horses, bikes or tractors. The gullies make access around the slopes impossible and concentrate water flow, which can lead to further erosion. Although the initial cause of tunnel erosion may be the presence of rabbit burrows or old tree root channels, it may also simply be a result of excessive subsoil waterlogging. The first sign is usually springs of muddy water spewing from the base of the slope during heavy rain.


Dense plantings of trees above and over the affected site may reduce waterlogging and help bind the soil. Interestingly, tunnel erosion is often evident within native forests and can be seen weaving around the roots of large eucalypts. Alternative species which form more dense root mats and are able to sucker from exposed roots may be more effective in controlling tunnel erosion than eucalypts. Planting trees or perennial pasture on any well-drained soils above the affected area may also help reduce waterlogging in the affected area.

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