Erosion control is all about keeping soil where it belongs; which is on our land and out of our waterways. This helps protect water quality and the plants and animals that live in and around our awa, so everyone – from people to wildlife – can thrive. Our science team have put a range of erosion control products through their paces to test their efficacy in keeping dispersive soils where they belong, as well as run long-term studies to find the best product and plant combination to protect cut faces. We use this knowledge to help inform your decisions around erosion control measures for short- and long-term erosion management.
As aquatic experts, we also know a lot about how fine sediment – both settled and suspended – can impact on our receiving freshwater and estuary environments. We also understand how the properties of different soils affect how long it can stay suspended, and the pros and cons of the different ways we measure suspended sediment. Our knowledge and experience means we can advise on sediment control measures that work best to intercept and trap different soil types once it has reached water, and the best ways to physically remove settled sediment entrained in the beds of our waterways that minimise impacts to the environment.
Keeping Loess in its Place: Helping Reduce Loess Runoff from Construction Sites Environment Canterbury
With leoss erosion a significant source of fine sediment to waterways fed by the Port Hills, Environment Canterbury and the Christchurch-West Melton Zone Committee commissioned us to develop a field study to help with erosion control in construction sites on the Port Hills. Our scientists developed a field-based experiment to test five locally-used erosion control methods (topsoiling, straw mulch, coconut fibre blankets, and two soil stabilisers: WRD-L and Vital Bon-Matt Stonewall) compared to untreated soil. Following a repeated measures design, simulating heavy rainfall, and capturing sediment runoff to be properly measured in the laboratory, we were able to quantify how each treatment performed under real-world conditions. We developed the field experiment to also allow for the involvement of community volunteers, who were able to take part in the science-led programme and to experience firsthand the dispersive properties of loess.
Our work provided council and contractors with much-needed insight into the practical benefits and limitations of erosion control measures on loess soils, which are particularly susceptible to erosion. Our findings, provided in a technical report, give an equitable comparison of the tested products that will help contractors to choose the product that works the best in terms of reducing sediment runoff and which is best suited to their local conditions. Our data also demonstrates that proper application and staged maintenance of erosion controls are essential for achieving reliable sediment reduction. These findings directly support updates to Canterbury’s Erosion and Sediment Control Guidelines, offering construction professionals valuable tools to improve site management practices.
Environment Canterbury’s Principal Resource Management Advisor, Nathan Dougherty, highlighted the significance of these outcomes: “The huge benefit of the research is that it gives everyone involved in the building process…the confidence to rely on erosion control techniques to dramatically reduce erosion on site.” This work sets a strong foundation for effective construction management on erosion-prone loess soils, aiming to protect waterway health across Canterbury and beyond.
Reducing Erosion: A Long-Term Solution for Loess Cut SlopesChristchurch City Council & Environment Canterbury
To address the persistent issue of sediment-laden runoff impacting Whakaraupō/Lyttelton Harbour’s water quality, we led an innovative field study under the Whaka-Ora Healthy Harbour initiative. Commissioned by Christchurch City Council and Environment Canterbury, this three-year project tackled the unique challenge of loess erosion from roadside cuttings – a sediment source in the harbour. Traditional erosion control methods are often ineffective for loess, so our focus was on pioneering sustainable, soft engineering solutions that minimise erosion at its source, whilst being cost effective to implement.
Working in collaboration with scientists at Manaaki Whenua Landcare Research, our study’s approach combined erosion control products with hardy native plantings selected for their resilience in harsh, low-nutrient loess soil. Five erosion control treatments were applied in test plots across a loess slope in the Christchurch Adventure Park. These treatments include rolled and sprayed mulches, along with six native plant species such as New Zealand ice plant and bracken fern, carefully arranged to test their effectiveness at stabilising the soil. Regular monitoring, supported by wildlife cameras, tracked plant growth and the effectiveness of erosion control measures, while also managing an unexpected challenge: possums with a taste for ice plants.
The insights from this research can help guide both council and private landowners on best practices for erosion control along loess cut slopes, with results shared publicly to encourage wider adoption. As part of Whaka-Ora Healthy Harbour, this project not only supports improved sediment management but also contributes to the long-term ecological restoration of Whakaraupō/Lyttelton Harbour, making a lasting impact on both the environment and community.
