Bank Stabilisation Works
Riverbank erosion is a natural process that can occur during a flood event, such as that experienced in Forbes and surrounds in November 2022. Bank erosion is expected to occur on the outside bend of a river and is a natural process of lateral river movement, however, if the rate, location or mode of bank erosion exceeds what is expected from natural processes, it may be the result of human disturbance at the site or in the catchment.
Erosion caused by natural processes is important to river function, however, where resulting in immediate threat to life and/or assets, industry best-practice can provide for an appropriate mitigation method to be implemented. Most areas of erosion will become stable over time by gradually battering themselves back to a stable angle. Stock exclusion and riparian revegetation should be considered in all areas to promote long-term stability.
Additionally, deposition of river sediment is a natural process and is expected to occur in areas of lower velocities such as the inside bend of rivers and will occur as flood waters recede. River sediment is essential to river function and should not be removed as it can provide protection in future floods.
Bank Stabilisation Works
The following is recommended when undertaking bank stabilisation works:
Bank erosion can be accelerated if riparian lands are not well vegetated with deep-rooted plants. Deep-rooted native species should be replanted in eroded surfaces to help stabilise riverbanks as well vegetated banks are also more resistant to under-cutting and slumping. Planting riparian lands with non-native plant species is strongly discouraged.
Bank stabilisation options are critical for the long-term viability of a riparian zone or waterway and include a well-structured vegetated riparian zone, fencing and stock management. Riparian vegetation can assist bank stability in the following ways:
- The roots of the vegetation reinforce the soils;
- Vegetation slows flow, reducing the erosive forces on the riverbank; and
- Vegetation cover armours the underlying soil from the wave and flow erosion processes.
For the reasons above, removal of large wood and native vegetation from waterways is not recommended unless it poses a serious risk to public safety or public infrastructure, e.g., large wood abutting bridges or other infrastructure after floods. Trimming, realigning or anchoring large wood should be considered before removal, however, if removal of large wood is necessary, professional advice should be sought.
As riparian lands are prone to weeds spread by water and stock access following a flood event, it is recommended that weed management activities should be prioritised and accompany revegetation works.
Working in Waterways
Waterways are sensitive environmental areas and as such, it is important that mitigation measures are implemented. Some basic mitigation measures are outlined below:
- Prior to works commencing within a waterway, erosion and sediment controls should be in place to ensure downstream environments are protected from ongoing sedimentation after a major flood event.
- Appropriate spill kits and contamination booms should be kept on site in the event of a spillage/leak. Emergency procedures should also be adopted as pollution incidents causing harm or potential harm must be reported to the NSW EPA.
- Refuelling of vehicles and machinery in an impervious bounded area more than 50m from the river or any drainage line and vehicles/machinery should be regularly maintained and checked for leaks.
- Required approvals/permits are to be obtained and necessary landholders and authorities must be consulted prior to works commencing.
- Due diligence should be completed including the consideration of Aboriginal heritage, non-Aboriginal heritage and threatened species or ecological communities.
Policy and Permits
Stock and Waterways - A NSW Manager's Guide
Guidelines for Riparian Fencing - NSW Department of Primary Industries
Soil Erosion Factsheets - NSW Department of Primary Industries
Removal of Large Woody Debris from NSW Rivers and Streams
Guidelines for Controlled Activities on Waterfront Land