River Stour Embankment Restoration

Salix assisted with providing a solution for a new commercial development, providing simultaneous erosion control and environmental benefits. 

This solution provided a continuation of the habitat whilst also achieving the requirements for erosion protection.

Salix were involved with an embankment restoration project, the supply and install of Shear Stress Turf, Coir Rolls and Rock Rolls, at River Stour Kidderminster. The opportunity arose from a new commercial development. 

The project consisted of regrading the banks of an urban section of the river Stour, where Salix materials were supplied.

The Design

Due to the nature of the enclosed site and the requirement for flood defence along the River Stour through Kidderminster, there is limited ability to restore this river habitat, however these habitats have a high ecological value and provide important habitat for fish and invertebrates.

The design philosophy for the project was to provide effective erosion protection, whilst ensuring flood capacity was retained and to increase the ecological value of the watercourse. 

Riverside planting in an urban watercourse requires prudent choice of plants, which may be tolerant to shade and high energy water environments. Pre-established coir rolls increase planting success, as the plants are mature which helps to reduce risk of plant failure. Adequate toe protection was required to protect the vegetation from high flows during peak events.

The face of the embankment was vegetated using Salix’s pre-grown Shear Stress Turf to ensure that soon after installation the vegetated embankment would be robust enough to thrive in periods of high flows which have the potential to occur quickly. 

The Benefits

Rock Rolls and Coir Rolls are used in conjunction on the project to provide mature vegetation, whilst also protecting the bank from erosion.  Plants were pre-established in 300mm diameter biodegradable Coir Rolls, placed behind Rock Rolls.

The plants had to be sufficiently robust to survive periods of high flows. Salix’s pre-established coir rolls are planted are typically grown for 8-12 months, providing mature native vegetation to increase success. Himalayan Balsam is present in the area, so mature vegetation helped to reduce the dominance of invasive species. 

The Shear Stress Turf was planted with a riverbank mix, consisting of a species rich seed mix.

The Rock Rolls utilise a 40mm to 75mm graded stone, providing robust erosion protection whilst allowing vegetation to establish. The small stone also increases the abundance and diversity of benthic invertebrates due to the larger surface area for them to colonise compared with traditional alternatives. The plants found within the coir rolls will colonised the wider area, including the rock rolls, providing greater ecological value. 

The high erosion control performance of the solution meant that a bioengineered solution was suitable as a direct alternative to rip rap. This saved the need for tonnes of imported material whilst creating sustainable and ecologically valuable solution. The shear stress turf provides long term erosion protection and vegetation establishment while permanently reinforcing vegetation. 

The various soft engineering solutions presented by Salix represent a major cost saving over traditional hard revetments.