We’ve been working with stakeholders for a long time to help them understand the linkages between riparian vegetation, flow and sediment supply dynamics, channel stability and river health. While we’ve worked on many great restoration projects across the country, Australia still has limited examples of successful, large-scale river restoration projects.
Restoring degraded rivers on a scale large is complex and expensive. Each river in need of restoration is unique. There are different stakeholder needs; community objectives, variations in climate, river and geological processes to understand; diverse local native vegetation to replant; and distinctive engineering problems to solve.
In this article we explore the benefits, processes and challenges of river restoration and discuss our role in advancing the science in large scale river restoration.
Flooding from Great Barrier Reef in Queensland to the Gippsland coast in Victoria
During the 2010–2011 Queensland flood disaster, the Mary River north of Brisbane rose 20 metres in some places, wreaking devastation in its wake. Just prior to this flood, but more than 1,500 kilometres away in coastal east Gippsland, Victoria, rivers such as the Genoa, Cann and Snowy were also flooding.
Both floods followed 10-year droughts, and both had potential to cause widespread economic damage.
In the Mary River, there was widespread erosion of riverbanks and floodplains, which the swollen river carried as sediment to the southern Great Barrier Reef. The huge sediment loads carried by the rivers on the Queensland coast in big floods affect the health of the unique plants and animals of the reef. The land of the river catchments may be impacted too: along the Mary River, agricultural lands were inundated; bridges, roads and parklands destroyed; and properties damaged.
The Mary River in flood inundates nearby agricultural land and affects infrastructure and homes in Maryborough, Queensland (Image: Alistair Brightman, APN Australian Regional Media)
But this is not a tale of two parallel floods. Before the 2010 Victorian flood, and following major flooding in 1998, Alluvium worked with the East Gippsland Catchment Management Authority (and its predecessors) to help restore the Genoa, Cann and Snowy Rivers.
Our objectives were to reduce the potential for erosion and sediment generation; create robust ecological corridors between the national parks and the coast; and establish river systems that could cope better with floods while providing for ongoing productive use of the floodplain. Unlike the Mary River, in the Cann River there were only minimal changes to the channel during the 2010 flood.
Our involvement with the Mary River happened later. Learning from our experiences in east Gippsland, and following the 2011 floods, we started collaborating with the Mary River Catchment Coordinating Committee in 2014. The Committee has had a long history of working with landholders within the catchment to improve riparian management practices. We worked with a diverse range of people to develop a restoration plan for the reach of river near Kenilworth, which is known to be one of the most unstable part of this river system. The plan focused on restoring streambanks, and instream and floodplain areas.
Both the Cann and Mary restoration projects have happened over large stretches of rivers and over long periods of time. They continue today. However, these kinds of projects are expensive and require a long-term commitment by governments, communities and landholders to succeed. So why invest in such projects?
The power of native vegetation to help rivers resist and recover from floods
Following the 2010 floods in Victoria, many communities blamed flood damage on the Victorian Government’s restoration of rivers and replanting of streambank vegetation. This resulted in a Victorian parliamentary inquiry, which triggered our investigations to better understand the effects of restoring streambank vegetation on rivers such as the Cann and Genoa.
We compared stretches of riverbank that had vegetation restored with those that had not. We paired similar sections of river for the comparison. We found that the reaches that had been cleared of native vegetation suffered much greater erosion than comparable systems where the vegetation had been restored over the past decade.
Where quality plantings of native vegetation had been established, there was between 80% and 95% less erosion. This meant that significantly less sediment headed downstream during the floods. There was also less damage to river channels and nearby infrastructure from flood waters, which are slowed by the vegetation.
Paired sites for Black Range Creek in north-east Victoria. At the site on the left, bare banks show some of the widespread erosion in the 2010 floods, while at the site on the right, the revegetated banks had only minor channel damage.
In Victoria, people designing waterway management programs started using native vegetation in the early 1990s to stabilise streams with the aim of improving river health. The programs included community engagement, the fencing of riparian areas, and the exclusion of stock from streams.
We found that the key to success in these waterway programs is to establish diverse native vegetation within the streams, on the riverbanks (10 to 30 metres wide on each bank), and into the adjoining floodplains. Suitable vegetation needs to include sedges and reeds (e.g. species of Phragmites and Typha) in the streams, and groundcovers, shrubs and trees on the riverbanks and floodplains. This kind of vegetation is effective at reducing the occurrence, extent and scale of floods. The reeds protect the soil from moving water; the branches and foliage of shrubs and small trees spread out and slow the water down; and the roots of larger trees provide strength to the soil, like steel in reinforced concrete.
It takes one unit of energy to move a grain of sand in exposed streambanks downstream, but if diverse native vegetation has established it takes over 100 units of energy before the underlying sand is mobilised. Not only does native riparian vegetation helps our channel systems resist floods, it also provides restores habitats for aquatic life. This is compared to conventional rock and concrete erosion-protection works, which can become deformed and fail after several flood events.
Vegetation within streams, like in this part of the Cann River, helps stabilise waterways and reduce erosion.
However, it takes anywhere between five and 15 years to establish vegetation with enough structure and diversity to be effective. Additional structural works may also be needed to help vegetation establish and grow. Whole stream reaches (encompassing several meanders), rather than isolated sites of erosion, need to be restored. While revegetation of a single site can protect it from erosion, revegetation of the entire system slows the water down and reduces the scale of flooding and damage to downstream communities.
For these programs to be successful, it is crucial that water managers design and implement management and ongoing maintenance programs. These need to be done in collaboration with local landholders so that establishing vegetation is protected, weeds controlled, fences repaired, and stock kept out of waterways. River restoration programs are not ‘one off’ seedling planting exercises, but long-term commitments to waterway vegetation care.
Policymakers need to support these programs through funding and complementary policy settings.
Restoring rivers on a large scale requires collaboration of all stakeholders
Bringing stakeholders such as landholders on board with large-scale river restoration projects is crucial for the success of such projects. And this is something brought home to us as we’ve worked on the Mary River restoration project.
Since 2014, we have worked with the Mary River Catchment Coordinating Committee, Burnett Mary Regional Group, Seqwater, Sunshine Coast Regional Council and local landholders to restore the stretch of river near Kenilworth.
Earlier clearing of land in the Mary River catchment in south-east Queensland, along with the extraction of sand and gravel from the channel, had straightened and widened the river by 40 to 60 metres. These changes to the river undermined the habitat of many species, including the endangered Mary River turtle, which is found only in this river, and the Mary River cod.
The Mary River turtle is found only in this river. It has a unique ability to breathe under water through specialised glands in its cloaca, a posterior opening for excretion and reproduction. This means the turtle, referred to as a “bum breather”, can stay under water for up to three days, growing an algal Mohawk on its head. The turtle relies on a healthy river to nest, breed and feed in. (Photo: Chris Van Wyk /ZSL/PA)
In our initial study in 2014, we found that about nine cubic metres of sediment is eroded per linear metre every year from a four-kilometre reach of the Mary River near Kenilworth. The sediment flows directly into the southern end of the Great Barrier Reef near Fraser Island.
After developing the plan to restore this stretch, all the stakeholders worked together to stabilise riverbanks; revegetate 3.5 km of riverbank and exclude stock from that area; control weeds; and change how dairy effluent is managed so it is prevented from seeping into the river . The total cost of investment so far has been more than $2.5million.
Before agreeing to this investment, stakeholders met to workshop what they valued most about this reach of the river. Some were concerned about the water quality affecting the reef, while others such as landholders were concerned about ongoing loss of land due to flooding.
The stakeholders agreed on four restoration objectives: decreasing erosion during floods; protecting the habitat of endangered species; protecting and improving water quality; and protecting and enhancing pools important for water supply, recreation and habitat refuges.
Although they had different values and perspectives, the stakeholders agreed that the objectives could be most effectively achieved through a combination of native vegetation restoration and stock management.
The improvements we have recorded within just a few years are impressive. In another five years, the vegetation should be similar to the vegetation that used to line the riverbanks prior to European settlement.
Photos of the same section of the Mary River near Kenilworth in 2015 (top) before restoration, and four years after revegetation and restoration (bottom) show how quickly vegetation can return when stakeholders work together.
The Mary River project is delivering environmental, social and economic outcomes. The river is healthier and its habitats more likely to support native animals, including endangered species. Some landholders are now reporting seeing platypus and Mary River cod in areas they hadn’t seen them in before. Once completed, this restoration will significantly reduce the sediments reaching the Great Barrier Reef lagoon, bringing better water quality to inshore reefs.
In 2014, the Kenilworth River Park lay next to a vertical bank of exposed riverbank 8 m high that was progressively collapsing into the river. Today, the Kenilworth River Park is a shady area on a shallow, gently sloping bend where people can picnic and listen to the flow of the river and the sounds of birds. This is helping to change the mindsets of previously sceptical landholders and other community members who now look to improve the riverbanks next to their land.
For Seqwater, the benefit of the project has been in protecting Kenilworth’s water resources. The device that takes water from the river (water offtake) had been threatened by rapid changes to the river channel, and finding an alternative water supply would have been very expensive. Seqwater is now confident that the town’s water supply is protected from future floods.
The completed works also reduce the impacts of floods through lost agricultural land and the costly repairs usually needed to roads, bridges and other infrastructure following a flood.
Meeting the challenges of investing in large-scale river restoration projects
In recent years, we have undertaken numerous projects across the nation to assess the fluvial geomorphology (the study of river processes and forms) and active changes in river channels. These projects have helped us and our clients to identify which reaches of rivers to prioritise for sediment-reduction programs that protect downstream areas, including the Great Barrier Reef lagoon, Moreton Bay, and water supply catchments. However, ongoing and long-term investment is required to implement large-scale river restoration projects in these areas.
While the existing long-term and large-scale river restoration projects appear to deliver a range of significant benefits to the people living on or near the rivers, there are few of these kinds of projects to point to. Why? The response of governments and others to floods is often to patch up the obvious damage rather than to look for long-term solutions.
There is an urgent need to address the fundamental issue: the loss of native vegetation along and within streams. This issue needs to be addressed by all involved in managing rivers: governments, waterway managers, scientists, engineers, interest groups, communities, and landholders.
Wherever there are rivers flowing from mountains down to the coast through agricultural land, there is likely to be a need to restore native riparian vegetation. This need encompasses the entire east coast of Australia, as the rivers flow down from the Great Dividing Range. Many areas of the east coast have steep, fertile floodplains where the native riparian vegetation has been so degraded that it is ineffective in protecting rivers and the land near them.
River restoration requires a long-term commitment and major investment by governments. We need landholders and other community members to agree to take responsibility for the success of restoration projects. Once vegetation is planted, it needs to be looked after. There is significant ongoing maintenance and adaptive management required, which means continued engagement and enthusiasm by all.
But the effort of committing to projects that restore rivers to health will more than pay off next time the inevitable flood follows a drought.
For more information
Ross Hardie, email: ross.hardie@alluvium.com.au
Misko Ivezich, email: misko.ivezich@alluvium.com.au
