Gully erosion is the removal of soil along drainage lines by surface water runoff. Once started, gullies will continue to move by headward erosion or by slumping of the side walls unless steps are taken to stabilise the disturbance. Repair work done in the early stages of newly formed gullies is easier and more economical than letting the problem go unchecked for too long. Large gullies are difficult and costly to repair.
What causes gully erosion ?
Gully erosion occurs when water is channelled across unprotected land and washes away the soil along the drainage lines. Under natural conditions, run-off is moderated by vegetation which generally holds the soil together, protecting it from excessive run-off and direct rainfall.
Excessive clearing, inappropriate land use and compaction of the soil caused by grazing often means the soil is left exposed and unable to absorb excess water. Surface run-off then increases and concentrates in drainage lines, allowing gully erosion to develop in susceptible areas.
Some of the problems caused by gully erosion include:
|dissection of the property causing access and management difficulties | |loss of productive land (gullies often occur in the most productive area of the catchment) | |reduced amenity and property values, including destruction of farm improvements, such as fences or tracks | |discolouration of water supply and sedimentation of waterways, dams and lower paddocks | |provides a harbour for vermin. |
To be effective, gully control needs to be tackled in two ways: by fixing the problems in the catchment and by stabilising the gully itself.
The object of catchment works is to reduce and divert theflow of water into stable drainage lines. This can be achieved by increasing infiltration rates and water uptake by plants and by diverting and storing water.
A practical way to begin is to subdivide the catchment into appropriate land classes and then apply grazing and cropping practices most suited to each class. The development of a land management or whole farm plan is an ideal way of identifying these issues.
Strategies for stabilising the catchment include:
|co-operatively tackling the problem by the formation of a landcare group could be be the most effective method where the source of the | |problem is spread over several properties | |diversion of water away from erosion prone gullies, thus dispersing the erosive power of the water over well vegetated areas. Diversion | |banks are a simple way of achieving this (see figure 1). | |contour cultivation where possible to slow down run-off and spread the water over a wide area | |maintaining farm tracks and culverts so that drainage is evenly dissipated and prevented from concentrating along any section. | |using trees and deep rooted perennial pastures to assist in both utilising excess water and reducing run-off. Again the development of a | |land management plan can be of assistance by identifying those areas which can be used for tree planting and pasture improvement. |
The object is to divert and modify the flow of water moving into and through the gully so that scouring is reduced, sediment accumulates and revegetation can proceed. Stabilising the gully head is important to prevent damaging water flow and headward erosion.
A variety of options can be used to get the...