Riparian restoration of river

The Upper East Barwon River is a vital waterway for Geelong and its surroundings. PhD candidate Mariah Sampson has been studying its riparian environment, and the impact of removing willows and restoration works on streams in the area.

The Upper East Barwon River is a vital waterway for Geelong and its surroundings. PhD candidate Mariah Sampson has been studying its riparian environment, and the impact of removing willows and restoration works on streams in the area.

Many years ago, willows were historically planted along waterways across Victoria for erosion control and aesthetic purposes. However, the spread of willows has been found to degrade rivers and riparian lands.

Barwon Water worked with Deakin University and Water Research Australia to assess the effectiveness of riparian restoration, with a focus on willow removal from a 3.5-kilometre stretch of the Upper East Barwon River. Mariah Sampson is a PhD candidate working with landholders and stakeholders to undertake this assessment.

Who is Mariah Sampson?

Sampson is from regional southeast Queensland. She grew up during the millennium drought, where her family relied on tank water.

“I think that gave me an appreciation for how important water was. However, it wasn’t until later that I fully appreciated it,” she said.

An important moment for continuing advanced studies in water research was in 2019 while doing an industrial traineeship with CSIRO Land and Water.

“I was in Brisbane, and southeast Queensland had a bad drought just before the bushfires began. It really motivated me to want to keep studying and exploring the balance between human and environmental water needs,” said Sampson.

Sampson’s PhD research topic is titled Evaluating riparian buffer zones in temperate streams, and she received the Nancy Millis Memorial Award in 2022. On receiving this scholarship, she found it a humbling and motivating experience.

“Nancy Millis was a very impressive woman,” said Sampson. “I’d like to live up to what the award embodies. It also represents how important water research is in Australia.”

What is her riparian restoration research about?

Sampson’s research focuses on the Upper East Barwon River, located outside Forrest, Victoria. Barwon Water transfers water from its West Barwon Reservoir via a 3.5-kilometre section of the East Barwon River. At this point, it diverts into the Wurdee Boluc inlet channel. It travels about 57 kilometres to the Wurdee Boluc Reservoir, where it is treated and supplied to customers in the greater Geelong region.

Willow infestation had caused a loss of transfer capacity through this section of the East Barwon River. The infestation of willows had reduced Barwon Water’s ability to transfer water and led to more frequent water logging of adjacent properties. Since 2019, Barwon Water has been working with local landowners and other key stakeholders to develop an agreed approach to removing the willows and remediating the river. These works were completed in May 2022.

“This combination of environmental, ecological and engineering goals is the sort of thing that I enjoy,” said Sampson.

In terms of her research, Sampson understands that the willows were planted in Victoria to deal with erosion following deforestation for grazing, agriculture, or logging.

“Willows tend to proliferate and are easy to plant. People can stick willow branches in the mud, and they will grow fast. Where they are endemic in Europe and North America, that makes perfect sense, and willows are not a problem. It’s only when they are planted where they are not supposed to be that it can become a problem,” she said.

It would have been hard for people to know this at the time, and they would have argued about the usefulness of the trees.

“These willows are now a problem,” said Sampson. “They are highly successful riparian invaders and have been linked with erosion and channel widening. They can grow and migrate into river channels. By blocking channels, they slow the river down and can reduce dissolved oxygen concentrations, resulting in potential problems for aquatic species.”

The importance of riparian restoration

Riparian restoration is considered one of the best ways to protect streams and tributaries from runoff. Sampson’s research is looking into better understanding the processes of restoring the land around waterways and whether this significantly influences water quality variables.

“Healthy riparian ecosystems can act as a mechanical and chemical buffer, slowing down sediments and preventing nutrients from running into waterways through processes such as denitrification in the soil or the uptake of nutrients by riparian plants,” she said. “Riparian buffers can also create habitat and habitat connectivity across landscapes while providing thermal buffering and shading for the stream environment. This canopy cover can also shade out pest aquatic plants that often reduce stream flow capacity. Some aquatic species have a limited thermal tolerance, so a healthy riparian zone can help to keep stream temperatures cool.”

The other significant impact is that a functioning riparian ecosystem can ameliorate flooding. This has been a big issue within the Corangamite catchment area. Geelong and the Barwon River fall within that catchment, which dealt with significant amounts of rain in the latter half of 2022.

“When willows are growing in the stream channel, a lot of rain can see the willows impede the flow of floodwater through the channel,” said Sampson. “That will see the water flow out over the floodplain and erosion of the channel embankment.  Improving the flow of water through the system is a key reason why willows have already been removed within the catchment.”

The ultimate goal of the research is to increase the scientific understanding of how replacing willows with riparian buffers that consist of native plants affects stream ecology, morphology, and water quality.

Dealing with local landholders and stakeholders

As part of her research, Sampson has been liaising with local landholders and stakeholders under the supervision of Brigid Creasey, a Water and Catchment Officer at Barwon Water. In her experience, the local landholders and stakeholders have been fantastic to work with.

“They allow me access to their properties, and they care about the river running through them,” Sampson said.

Sampson pointed out that talking to the local landholders can be important for additional information and context. This is particularly true when some have been using the same land for over 60 years.

“For part of the study, we looked for sites that do not have willows or revegetation.  These additional sites have native riparian trees, such as the Australian blackwood (Acacia melanoxylon),” she said. “We have talked to some landholders who would tell us that the blackwoods have been there for 65 years, or they might tell us that the blackwoods were planted after the streams were straightened at some point in the past. We have also seen landholders doing their own restoration and bringing back the original meander. On at least one occasion, an owner said that a particular point in the river was three to four metres deep. It did not look deep, but when we measured it, we found out that it was. That background knowledge of landholders is vast.”

Another stakeholder of note is the Corangamite Catchment Management Authority. Sampson said that she collaborates with them regularly.

“They have also connected me with landholders and different sites across the region. I also try to keep them up to date on what I am up to. ” Hopefully, my research results will be useful for their forward planning,” she said.

Support of Water Research Australia and her future

Many early career researchers in the water industry have pointed to the support of Water Research Australia (WaterRA). Sampson agrees that WaterRA has done a fantastic job of supporting her.

“They have connected me with a mentor within the water industry and other great women in water science and management,” Sampson said. “They also have a great research capability manager who takes care of all the students, ensures that everyone’s funding arrives, organises social events and encourages students to attend conferences. WaterRA is a great support.”

In terms of her future, Sampson sees herself in the water industry.

“I want to get some solid findings from my research first and then to be able to communicate it in a meaningful way to landholders, industry, and catchment management authorities. I’d love to work in the water industry, especially catchment management. It’s only going to become more important in the future.”

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