Erosion is the natural process by which water, wind, waves and other natural actions wear away the earth’s surface. Vegetation clearing and livestock grazing lead to increased erosion and cause the soil to wash into rivers and creeks.
Reducing channel erosion can make a difference in the:
- home - improved property management
- paddock - retaining fertile soils
- catchment – reducing sedimentation and improving fish habitat and water quality
- community - improving resilience.
What is channel erosion?
There are two kinds of erosion between the banks of a channel:
- streambed erosion
- lowering of the bed
- revealed by small waterfalls or ‘nickpoints’ in the channel bed
- streambank erosion
- on the bank
- often in the form of scouring, slumping and subaerial erosion.
- on the bank
Streambed erosion is the main cause of streambank erosion.
Streambank erosion occurs when water flow takes sediment from one part of a stream and deposits it at another. Streambed erosion is usually the most common, the most destructive and the most difficult to identify.
Impacts of erosion
On-site changes include:
- reduction in soil health
- soil loss
- paddock dissection
- reduced property values.
Off-site changes include:
- poor water quality
- loss of in-stream habitat
- damage to public infrastructure
- increased transportation of nutrients with run-off.
How can I stop channel erosion?
The first and most difficult step is to identify the underlying causes. Ask your local LLS office for help. Some of the steps you can take to stop erosion and rehabilitate streambanks are outlined below.
Step 1: Look after the best bits first. You will get far more benefit from your effort and money by identifying and protecting the riparian areas that are not degraded.
Step 2: Remove the existing pressures. Pressures may include livestock grazing and pugging impacts, weeds, nutrient inputs or damage caused by vehicle tracks. Sometimes, removing these pressures is all you need to do and the stream will naturally repair itself.
Step 3: Ensure the streambed is stable, and/or restore appropriate streambed levels. Some people still consider removing woody debris when they see bank erosion. But the issue is more likely to be a lack of streambank vegetation or even streambed erosion, which may need structural work, like the log groynes pictured here. If there is no streambed erosion, move on to Step 4.
Step 4: Stabilise the toe of the bank first. Form a low bench next to the toe of the bank and densely plant it with suitable plants to prevent undercutting and further erosion.
Step 5: Plan the project to allow natural channel adjustment. Channels are rarely fixed and erosion will continue until plants are well established. Plant as if there will be more movement and don’t plant trees at the top of steep eroding banks.
Step 6: Densely revegetate the remaining bank. Plant a range of native species to provide adequate groundcover, understorey and overstorey. This imitates natural vegetation density and cover. Plant hardy, fast-growing pioneer plants first and more fragile, sensitive, slow-growing plants later.
Severe erosion and streambed erosion
More severe sites of erosion, including streambed erosion need ‘harder’ solutions that are often more expensive and may include:
- rock or concrete ramps or log sills to reduce water energy
- rock or log bank protection
- rock groynes or mesh fencing to redirect the flow
- rock or log structures to encourage sediment deposits and allow the bank to re-establish.
Revegetation of any erosion site with native trees and shrubs also provides long-term benefits.
It is important to obtain permits for in-stream works. Call your Local Land Services office on 1300 795 299 for more advice.
Key points to remember
- Erosion is a natural process.
- Lack of streambank vegetation is a major cause of bank erosion - not woody debris.
- Streambed erosion is often the most difficult form of erosion to identify.
- Streambed erosion can often lead to streambank erosion.
- Removing pressures such as grazing cattle or vehicles is the first step towards stabilisation.