Bank Stabilisation Works

General Considerations

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:

  • All soil, fill, gravel, sand and rock used for stabilisation works should be certified VENM (virgin excavated natural material).
  • Professional engineering and/or geomorphic advice should be sought before attempting to implement engineered stabilisation works.
  • Consider both natural recovery potential of unstable banks and/or relocation of the threatened asset. The cost of and timeframe required to prepare engineered designs, secure available funding and undertake works may warrant consideration of the relocation or decommission of asset under threat.

    Bank Reshaping

    The following is recommended when undertaking bank reshaping works:

  • Berms may need to be introduced to steep banks that are higher than 3 metres, or where erosion is expected along the toe of the bank. A typical berm width is one metre wide.
  • Establishing a berm on a watercourse bank can provide the following benefits:
    • If bank erosion occurs at the toe of the bank and this erosion results in soil slumping on the bank, then the berm can reduce the area of the bank over which this slumping occurs.
    • Bank berms can be used to increase the stability of steep banks.
    • Berms can be used to delay the effects of soil erosion around the root system of establishing trees.
  • If bank reshaping works are required, a bank slope of 1(V):2(H) is recommended.

Vegetation Management

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

Heritage

  • All Aboriginal sites in NSW are protected under the NSW Parks and Wildlife Act 1974.
  • If planning an activity that may disturb the ground or old growth trees, you must show that steps have been taken to avoid damaging or harming any Aboriginal site or object.
  • In the event items of Aboriginal Cultural Heritage are uncovered during works, works must cease and NSW Department of Planning, Industry and Environment NSW DPIE) are to be notified.

    Fisheries Management Act 1994

  • Part 7, Division 4 of the Fisheries Management Act 1994 specifies that ‘A person must not harm any such marine vegetation in a protected area, except under the authority of a permit issued by the Minister under this Part’. Marine vegetation includes mangroves, seagrasses or any other marine vegetation declared by the regulations to be marine vegetation.
  • Part 7, Division 3 of the Fisheries Management Act 1994 specifies that ‘A person must not carry out dredging work or reclamation work except under the authority of a permit issued by the Minister.’

    Water Management Act 2000

  • If works are undertaken by or on behalf of a Public Authority works are exempt from obtaining a Controlled Activities Approval. Best practice must still be applied.

    Vegetation Removal

  • If proposal involves damaging threatened species of flora or fauna or habitat under the Biodiversity Conservation Act 2016, you must consult with NSW National Parks and Wildlife Service (Threatened Species Unit).

    Land Ownership

  • Most beds and banks of waterways are Crown land. Consent is required to carry out works or activities on Crown land.

Helpful Resources

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