Erosion Indicators - Arid and Semi-Arid Areas

Erosion is a natural and continuous process. Soils are created through erosion of parent material and either local deposition or transport and deposition elsewhere. The concern is not erosion, but accelerated erosion.

The trigger for accelerated erosion in arid and semi-arid areas is loss of vegetation cover, this can be caused by long-term climate change or more immediately as a result of overgrazing. Loss of vegetation cover exposes soils to wind and water erosion, loss of soils decreases the potential for vegetation production. The end result is a decreases in the carrying capacity of the rangeland. Despite being in arid and semi-arid areas the erosion is largely a result of infrequent but heavy rainfall events.

There are three forms of erosion characteristic of degraded arid and semi-arid rangeland areas:

- Sheet Erosion - the most common form of erosion. Unprotected soil particles are loosened by trampling, through wind erosion and by the impact of rainfall. The soil particles are then transported by rainwater surface flow to the river and stream systems. Sheet erosion is characterised by a general lowering of the soil level, leaving raised pedestals where the root mass of the remaining vegetation protects it.
- Wind Erosion - less common, but again takes place after vegetation has been lost and when soil particles are loosened. Early signs of wind erosion include deposition of sand particles around plants and micro-ripples on the surface of exposed areas. The final extreme is the classic sand desert dune structures.
- Gully Erosion - the most obvious and dramatic demonstration of erosion, although in most areas actually less significant in terms of total land degradation. Gully erosion rarely occurs without sheet erosion. The trigger for gullying can be the loss of vegetation in areas where the microtopography results in concentrated streamflow during the rains. They can also be triggered by erosion along livestock tracks, footpaths and road edges. The process can start with "rills" and end up with gullies that are tens of metres deep.

Sheet Erosion

Surface flow patterns indicating active sheet erosion

Soil pedestal protected by the root mass of the plant, while surrounding levels are lowered by sheet erosion.

Continued sheet erosion results in larger pedestals

Parent material and eroded parent material exposed by sheet erosion

(Back to top of page)

Wind Erosion

Sand piled against the base of plants and microripple caused by wind erosion

(Back to top of page)

Gully Erosion

Extensive sheet erosion; rills deepening into small gullies

Advanced sheet and gully erosion exposing lower soil horizons and pebble layers

Major gully systems

(Back to top of page)

> > [Livestock & Environment Toolbox Home]