New talent trials novel tool to control sediment
Our new Land Management Advisor - Christchurch West Melton, Carys Marulli de Barletta, is trialling a fresh approach in the Port Hills by planting an exotic grass species to prevent erosion and sediment loss from polluting our urban waterways.
A lot of the sediment in Christchurch’s waterways comes off the Port Hills. When soil erodes, sediment makes its way to our rivers and streams and acts as a contaminant — negatively affecting water quality, smothering aquatic habitats, and damaging fish gills. Combatting sediment loss is key to protecting our rivers and streams.
Tunnel gully erosion on the Port Hills
The Port Hills area suffers from tunnel gully erosion.
Tunnel gully erosion is a common problem for rolling, hilly landscapes. It occurs when water runs through soil downgradient, and takes layers of subsoil with it. Over time, what’s left is a hollow ‘tunnel’ under the soil’s surface. Eventually, these tunnels can collapse to form open gulleys or channels, which are visible on the terrain.
Tunnel gully erosion affects soil quality as well as land stability, dumping sediment downstream and making the landscape more at risk of severe slips.
Land Management Advisor - Christchurch West Melton, Carys Marulli de Barletta
Trialling vetiver grass for sediment control
Carys is working on the trial with a private landowner in the Port Hills to improve freshwater quality in the Christchurch city catchment. The trial involves planting a variety of vetiver grass, a commercial non-fertile exotic grass, where tunnel gully erosion is occurring and then measuring sediment loss downgradient.
“Vetiver is an exotic grass species that’s quick to establish a robust root system, and is very drought tolerant,” says Carys.
“These roots act to bind and stabilise the surrounding soil, reducing the risk of earth being easily washed away by wind or water. We’re also excited by the idea that vetiver may have fire-resistant properties, making it a great fit to trial on the hills around Christchurch.”
Research on erosion control theorises that using this fast-establishing exotic grass to swiftly stabilise soil, will give native vegetation, if planted, the chance to flourish too. Because vetiver is shade intolerant, once native vegetation becomes dense, the vetiver grass will die and leave behind a section of established native bush.
Carys and her team will use strategically placed sediment traps to measure how effective the trial is at preventing soil loss.
The data will then be assessed against the same type of planting trial, but with native vegetation instead, to see how the species compare.
Carys measures vetiver grass on the Port Hills
Carys checks a sediment trap
Summer student-turned-staff
Originally working on fish passage and willow mapping with the regional biodiversity team, Carys joined us as a summer student in 2022 while completing a Bachelor of Science in Biological Sciences from the University of Canterbury.
At the end of her studies, Carys came back - this time as a staff member.
She began as a resource management officer, and recently pivoted to land management advisory, delivering on-the-ground advice for urban issues like stormwater management, pollution prevention and contamination control.
In her role, Carys works in collaboration with rūnanga, landowners, and community groups to deliver land management advice and other special projects for central Canterbury.
“Working in land management in an urban area means that my day-to-day is a bit different than my colleagues who support the rural communities in our region,” says Carys.
“As someone who is passionate about freshwater quality, I love the opportunities I have in this role to proactively work with landowners and businesses on innovative solutions to prevent pollution in our waterways.”