Norwich Northern Distributor Road

28th February 2018 WeDigJames

Roadside swales were treated with a high performing hydroseeding solution to quickly establish plant growth and prevent heavy metals and salts from entering the wider environment.

Our easy to apply TerrAffix®-Swale stops pollutants from contaminating land and water and results in bioengineered green swales in a matter of weeks.

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Vegetation growth by December 2017, five weeks after application Norwich Northern Distributor Road (NDR) 1

Norwich Northern Distributor Road (NDR) Sub-soils prior to swale establishment

Compacted aggregate of low porosity on the Norwich Northern Distributor Road

Addition of TerrAffix-Swale biochar and HydraCX to the hydroseeding tank

Poor soils in swales on the Norwich Northern Distributor Road

Norwich Northern Distributor Road (NDR) Swales over-sprayed with TerrAffix-C biochar and HydraCX

Grasses established in the swales five weeks after TerrAffix Swale was applies Norwich Road Distributor

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Vegetation growth five weeks after application on the Norwich Northern Distributor Road

Site Problems

Type-1 fill material had been used on the swales, leading to extremely difficult conditions for vegetation establishment, as there was little or no soil on the compacted aggregate
The subsoils on the roadside swales comprised of a high percentage of clay and silt, decreasing the soil porosity and exacerbating the drainage problems of the area
Road runoff including potentially harmful salts, heavy metals and pollutants required attenuation before contaminating soakaways, rivers and streams
The area has special protection aquifers covered by the Highways Agency’s environmental statement, which stipulates that the implementation of a sustainable drainage solution to slow the flow of water and decontaminate road pollutants was essential

This was a large road building project which involved the creation of 28km of green engineered roadside swales on either side of 14km of new dual carriageway.

A huge surface area of 88,000m² of swales required soil amendment in order to establish vegetation and attenuate runoff, preventing land pollution.

Solution

TerrAffix-Swale was used as an additive to HydraCX and was applied directly onto the compacted aggregate of the roadside swales using a hydroseeding unit. Using this unit meant that health and safety issues were reduced substantially in this soil amendment project and there was no requirement to import expensive topsoils.
In combination with the proprietary mix, TerrAffix-Swale provided nutrients and minerals for the seed mix that was specifically designed for the particularly poor soil conditions. This enabled rapid vegetation establishment with significant grass cover within six weeks to help establish the SuDS quickly.
Soil structure, soil aeration and water retention within the root zone of the growing plants was enabled, ensuring the long-term maturation of the vegetation and a bioengineered solution to filtering pollutants from highway runoff before they cause water pollution.
The successful plant growth increased the roughness of the swales’ profile and created a high surface area, improving water filtration properties, leading to better land drainage and decreasing the likelihood of future flood events.
The large surface area of the roadside swales effectively and sustainably attenuates road runoff, locking in carbon and refractory carbon.
TerrAffix-Swale’s biochar content ensures that the green swales’ carbon sequestration abilities have established a functioning ecosystem on the side of a very busy road. The longer term benefits of CO² sequestered by photosynthesis as the vegetation matures ensure that this SuDS project will only continue to have positive impacts on the wider environment.

Balfour Beatty required a bioengineering solution to sustainably treat the roadside swales built as part of the Norwich Northern Distributor Road in Norfolk.