Managing riverbank erosion

Understanding river behaviour

The faster water flows, the more power and energy it has to carry material with it. Slow moving water will carry sand, silt, and gravel. Faster flowing water is capable of carrying larger material like rocks and tree trunks. Water speed can be slowed by curves and bends, and obstacles. 

This video explains the key concepts of how river condition effects water flow and river behaviour.
 

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Causes of riverbank erosion

Erosion and deposition of sediment are natural river processes. However, rates of riverbank erosion can be accelerated by flood events, removal of native vegetation, land management practices, stock grazing, mowing and boat wake.

These pressures prevent regeneration of native trees, shrubs, and groundcover leading to: 

• loss of productive land
• loss of habitat and diversity
• reduced water quality. 

When creek banks are disturbed or overrun with weeds, they cannot repair naturally between flood events. Supporting native vegetation helps the riverbank stabilise and recover over time.

This video explains river behaviours and conditions that cause erosion including:

• scouring
• bank composition
• stream-bed lowering,

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Ways to manage riverbank erosion

Before starting any erosion control work, make sure:

• you know who owns the land and your responsibilities.
• your work will not harm threatened species or ecological communities.
• you have checked whether approvals or permits are needed. 

Many riverbank erosion works do not need a licence or permit. These can help protect your riverbank and improve riparian health. 

Activities that do not need approval include:

• Fencing off the riparian zone to keep livestock away from the riverbank. It is important that you:
  • Aim for at least 10 metres between the fence and the bank. 20 metres or more is better for larger streams or erosion-prone areas.
  • Provide off-stream watering points or controlled access if required.
• Widening and improving riverbank vegetation to promote groundcover to bind soil.
• Retaining fallen timber and rocks. This can help slow water movement, strengthen banks, help establish vegetation and provide habitat.
• Limiting people, vehicle and machinery movement and access to the riparian zone.
• Using natural materials such as hay bales, mulch, jute mesh and coir logs to minimise run-off.
• Avoiding work on streambanks when they are still wet. Only start work when the ground has dried out enough.

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Ways to strengthen your riverbanks

The guide to managing riparian areas covers a range of property management strategies to maintain riverbank integrity and reduce the risks of erosion including:

• fencing
• grazing management
• weed control

Active erosion will require more intensive repair. 

The role of woody debris

Woody debris, such as fallen trees and branches, plays an important role in healthy waterways. It reduces erosion by slowing water flow, traps sediment and provides essential habitat for fish and aquatic life. 

Following flood events, you can remove flood debris from fence lines and other built, land-based assets and use it to strengthen your river system.

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Video transcript

Woody debris for riverbank rehabilitation

Giinagay, hi, my name's Logan.

I'm a senior environmental officer

at NSW Soil Conservation Service.

I'm really lucky to work on country that always was

and always will be Gumbaynggirr land.

Woody debris is not only important,

it's essential to the health of our creeks and rivers

here in New South Wales.

It has three big functions.

Firstly, it's essential for habitat and biodiversity.

So it creates lots of little pockets and niches

for fish and other animals to live.

Secondly, it's really important for stability.

It helps to protect against bank erosion

and importantly bed erosion as well.

And the other thing is wood is really good for water quality

because it helps to cycle that surface water

with the groundwater and it filters out nutrients

and other bits in the water that keep it really healthy.

Before this land was cleared for farming,

the Gumbaynggirr ancestors would have walked through

dense forests all throughout these floodplains.

And that dense forest would have provided

constant source of input of big lots of wood

into these waterways.

In fact, not too far from here

they dated an old log they found in the gravel

to 20,000 years old.

So we know that that wood is really persistent

and essential part of the structure of all these systems,

even though it's very complex and always changing.

Trees falling in on isolated cases can cause erosion.

But if we take a step back and look at the bigger picture

of a river, we know that having lots of wood

and a messy system slows the water down

and it helps deposit sediments,

both in the channel and on the floodplain

and it creates lots of pools.

And those pools are essential for things to live in

and also to further help with flood mitigation.

When water hits woody debris in the channel,

it forces it to move over, under,

and around that obstruction.

And in doing so, it creates pools.

It also creates riffles.

And that pool riffle sequence is essential

for having a healthy river, particularly for fish

like the threatened Murray Cod and Eastern Cod,

which rely on those pools to survive.

Fish love hanging out under logs and within snags.

But not only fish, lots of other organisms

that exist in the creek need that shade

and need a little pocket where they can get away

from predators and raise their young.

So, wood's essential for habitat.

It does seem practical to want to realign woody debris

when it's fallen in a river, but we need to understand

that we're not just dealing with our own properties

We need to be thinking about the entire catchment.

When it comes to moving woody debris,

there is a reason why permits are required

>and it's so that we can maximise the benefit of that wood,

but also prevent against those isolated pockets of erosion.

It's important that when you're thinking about moving wood,

you really want to engage professionals

who've done it before and can understand

the way that the system works.

Many people think that big build-ups of woody debris

will increase the flood risk, but in actuality,

you have the same volume of water moving through the channel.

Those logs are slowing the water down,

which is reducing the erosion potential downstream.

Coir logs and sediment control

Coir logs are rolls of organic fibre such as coconut, enclosed in mesh and held in place with stakes. They are used to protect disturbed creeks and gullies and help new plants grow.

When using coir logs, you should:

• Add material at the toe of the bank to prevent erosion uphill of the logs.
• Cut stakes level with the coir log surface to avoid flood debris snagging. 

Installing timber fillets (large woody material)

Timber fillets use fallen or cut trees that would otherwise be burned or chipped. Logs are bundled and placed along the base of the riverbank where a shallow intertidal bench exists.

When making timber fillets:

• Use posts made of logs 150–200mm in diameter and 2–4 metres long.
• Use horizontal logs 350–600mm in diameter and up to 7 metres long.
• Secure horizontal logs to vertical posts to form a stable barrier.

Timber fillets reduce wave and wind energy, slow water flow and create spaces for young mangroves or native plants to establish. This eventually stabilises the sediment deposited on the intertidal bench. 

Revegetating riverbanks

Planting native vegetation stabilises soil, reduces erosion and slows water flow during floods. This can protect riverbanks by helping to prevent undercutting and scouring. This is especially important during high-flow events.

Read more about revegetating waterways.

Intensive riverbank repair works

Damaged riverbanks along high-value rural agricultural land, or where cultural and environmental assets at risk should be actively managed.

Before beginning any in‑stream or bank works, check what approval pathways apply to your property and proposed activity.

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Riverbank works that may need approval

Landholders are responsible for checking and obtaining all required approvals before starting any work. You may need approvals for activities like:

• using machinery for earthworks
• removing or disturbing in-stream woody debris
• clearing or cutting riparian vegetation
• bringing in fill or excavating with machinery
• building rock, concrete or other hard structures on the bank
• installing in-stream structures that block fish passage.

Contact your local authority for advice before starting any controlled activity.

On-ground success stories

Watch how Hunter Local Land Services, Soil Conservation Service and private landholders restored 700 metres of riverbank at Millers Forest using timber logs and revegetation.

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