Colchester City Council- Riverbank stabilisation using NBS

The majority of the world population live close to water, with almost all European capital cities being found along rivers. Historically, this provided a means of transporting people and goods, facilitating trade and migration which accelerated development. However, living in proximity to water has its drawbacks; flooding and erosion being the main examples. The severity of erosion is subject to many factors such as geology, topography and can be exacerbated by frequent high-energy events such as storms. To combat this, humans have devised many techniques for limiting the damage caused by erosion and flooding, the majority using concrete and other hard engineering methods. Steel sheet piling is generally used along urbanised sections of riverbank, maintaining the stability of the riverbank while protecting against erosion. While hard engineering proves considerably effective, it does not solve the problem entirely which is typically displaced to another location, with the use of concrete also having a negative environmental impact. Currently, the most appropriate solution is generally identified using a triangulation approach, where trade-offs between social, economic, and environmental factors can be assessed.  

Earlier this year, we were approached by Colchester City Council, who were considering options for repairing a section of collapsed sheet piling around a sewage outfall on the banks of the River Colne. The failure of the sheet piling has resulted in the collapse of a public footpath which runs alongside the Colne and has also exposed Fieldgate Quay to erosion. Fieldgate Quay currently houses many light industrial buildings as well as Colchester sewage treatment works. We have worked closely alongside the client and stakeholders to develop a collection of possible solutions, in line with their strategic plan for 2020-2023. We looked to satisfy aims such as promoting climate resilience within the community, biodiversity growth as well as encouraging green and innovative solutions to the climate emergency.

As part of the initial planning stages of the project, it was necessary to conduct an analysis of the site including soil examinations and riverbed bathymetry investigations. Environmental assessments such as Water Framework Directive (WFD) and Habitat Regulation Assessment (HRA) were conducted to identify nearby sensitive areas which are covered by environmental legislation. This helps to inform decisions regarding if formal impact assessments must be completed, for the purpose of minimising ecosystem disturbance and impact on wildlife. After these had been conducted, potential solutions were collated, and prepared for consultation. The proposed works include re-engineering of the river bank to accommodate an intertidal set back terrace alongside the use of specific habitat features. This has a variety of benefits, such as the opportunity for creation of a saltmarsh or reedbed terrace which can decrease risk of flooding by creating more room for river flow.

Example of an intertidal terrace at Royal Wharf, London (Source: EstuaryEdges.com)

In recent years, a rise in environmental consciousness has facilitated a shift in longer term thinking and the need to work alongside nature when considering priority areas for protection. Nature-inclusive solutions help to develop more sustainable management techniques which are resilient and prioritise habitat creation and biodiversity gain. Our eco-piling habitats have been engineered to work alongside nature to protect areas vulnerable to erosion. We use our GeoBlock® technology to recycle aggregate and produce our concrete, reducing the reliance on virgin sand and promoting a circular economy. Additionally, our eco-piling habitats have unique surface textures which encourage biocolonisation, as well as macro features such as cups which replicate natural environments in the intertidal zone. While the works have not yet commenced (planned for 2023), we are excited to continue collaborating with CBC on this project to stabilise the riverbank and creating new opportunities for wildlife to flourish. Watch this space!