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Stream bank erosion | LC0096 |
David Ziebell, Leongatha
November, 1999 |  |
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Stream bank erosion occurs under natural conditions, particularly during peak storm flows and is part of an on-going cycle of sediment erosion and deposition within the stream system. However, large-scale changes to streams and their catchments since European settlement has greatly accelerated this process and many streams have become potentially unstable as they seek to find a new balance.
What causes stream bank erosion?
Increased run-off from cleared catchments has placed considerable erosive stress on streams, especially where the majority of the catchments have been cleared. Clearing of stream-side vegetation and unrestricted stock access to streams are also significant causes of stream bank instability. Where local soils do not have the necessary strength to resist water erosion, the removal of protective vegetation can lead to extensive erosion.
In the past, many streams in Gippsland drained into wetland areas before entering the sea. These wetland areas were drained for agriculture and rivers often straightened and de-snagged. As a result, the water velocity tended to increase along the length of the stream. This kind of treatment heightens the potential for erosion - unless structures are introduced into the stream to slow the flow of water.
Other factors contributing to stream bank erosion include:
- direct access by vehicles and stock to the banks of streams
- rabbits, which can reduce plant cover and slow revegetation efforts by eating young seedlings and weaken banks by burrowing
- fallen logs and other obstacles which forces water to flow around them into the stream bank, causing undercutting
- willow trees, which often regenerate where they fall or lodge, thereby creating in-stream islands which again forces the flow of water into stream banks
- deepening of the stream bed, either through dredging or increased water velocity, can result in a steeper stream bank angle. This causes the stream bank to collapse at a later stage as the bank readjusts to a gentler, more stable angle.
What damage does stream bank erosion cause
Damage caused by stream bank erosion includes:
- loss of what is often regarded by landholders as the best agricultural land
- damage to roads, bridges and levee banks
- invasion by noxious weeds once native vegetation is depleted and soil is exposed.
- reduction of vegetated streamside verges and the subsequent loss of recreational and environmental values.
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Managing stream bank erosion
The proper management of stock is most important in the protection of stream frontages. Where stock have unlimited access to the stream along the entire frontage, little can be done to preserve the stream frontage.
In most cases, fencing of the stream combined with well placed watering points may represent the best solution. A distance of 20m from the water’s edge is usually considered the minimum required for bank protection. A simple, non-robust electrified fence is probably the best form of fencing as it offers least resistance during flooding and is easiest to re-establish should damage during flooding occur.
In areas where stock need to be excluded from damaged banks, concrete or gravelled walkways can allow stock access to water. Alternatively, off-stream water storage could be provided.
Where possible, remnant vegetation needs to be protected and maintained as flooding and access problems may make revegetation works difficult. Also, once the original vegetation has gone, costly erosion control structures may need to be built prior to embarking on revegetation works.
If revegetation work is necessary, then aim to re-establish a variety of indigenous plant species including grasses, sedges, shrubs and trees so that maximum ground cover and protection is achieved.
Avoid planting species such as willows and poplars which can significantly alter the ecology and physical structure of the stream. If a willow eradication program is considered necessary then it is preferable to either ringbark or poison the trees so that they decline gradually while native vegetation is re-established. Removing the whole tree including roots in one operation will leave the banks vulnerable to erosion.
Indigenous vegetation
Some examples of indigenous stream bank vegetation found growing in South Gippsland include:
Trees:
Shrubs:
Grasses and Sedges:
General comments
Stream frontage works will often involve several landholders, depending on the length of the stream and the extent of degradation. In this situation, local Landcare groups could be one way of tackling the problem and at the same time be a means of attracting technical and financial assistance. There are already several successful examples of this occurring in Victoria.
Further information
In the case of major stream erosion, the relevant Catchment Management Authorities should be consulted, as the resources and knowledge required for the stabilisation works may be beyond that of individual landholders.
Advice and assistance on stream bank erosion and revegetation works can be obtained from your local Department Of Natural Resources & Environment office, Phone: 136186.
Acknowledgements
This document was initially produced for the Farmcare Program with assistance from the National Soil Conservation Program.
This note replaces note number SC0042.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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