Rock Rolls and VMax C350 providing erosion control at Yeoville Junction

Railway Embankment Improvements at Yeovil Junction Adjacent to a River Yoe.

Erosion concerns at the railway line, Yeovil Junction, required a robust but ecological response.

Salix advised Hyder Consulting (Arcadis UK) and supplied Suttle Projects for the sheet pile toe protection. As this river is a haven for wildlife the Bridgwater office of the Environment Agency monitored the solution.

Traditional sheet piling was used directly under the railway line and then Rock Rolls were used at the toe to protect from scour, whilst the bank above was seeded and then VMax C350 was placed over the surface to protect the seeds below and provide long term permanent reinforcement for established vegetation.

The Rock Rolls and turf reinforcement mat VMax C350 were installed in October 2014. The grass emerged quickly from seeds sown beneath the matting protected initially from 3m/s flows and which will then resist 6m/s flow on reaching maturity.

Rock Rolls (and Rock Mattresses) protect loss of underlying soils in flows of 8m/second.

Rock rolls will attract and stabilise silts which are colonised by plant material. Un-colonised Rock Rolls are habitats for many invertebrates above and below the water. Work with Swansea University’s SEACAMs department has shown how effective the system is at preventing erosion whilst providing essential habitats for invertebrates.

Dr Ian Dodkins of SeaCams said in a recent newsletter

“Salix’s innovative rock roll system suspends granite boulders* that are approximately the size of a fist in a tough polypropylene netting to form tubular revetments.

The efficacy of this system in preventing erosion is in no doubt, being successfully deployed in the field for many of their current clients….

We can clearly see that the size of the spaces between the rocks are critical to the establishment of a healthy aquatic environment. Even at this early stage we are seeing the inability of rip-rap to establish a high enough density of invertebrates to create the environmental conditions for a healthy aquatic environment, while twice the numbers of invertebrate have been identified in both the Rock-Roll systems

*We carefully fill the nets with river gravel sized stone that quickly blends into the environment by replicating natural river bed function and improves the anti-erosion performance.