Sustainable urban Drainage Systems (SuDS) are an important water runoff management system in all new housing developments. TerrAffix Soil Solutions were brought in to stabilise the bare soils around the balancing ponds within the SuDS at a housing development in Sussex.
The exceptionally wet and stormy weather has caused problems across the UK, in particular on areas of bare or exposed soil. Our approach was to stablise the soil using natural materials, that will biodegrade into the site. We used fast growing seed species with a net forming root structure. The soils were anchored using biodegradable blankets which provide shelter for the germinating seeds and will break down adding organic matter to the soils over time.
The main objective is to minimise and trap soil from being displaced by rain impact and then transported within the surface water flow, off sites and into streams and rivers.
Our approach to soil stabilisation works with the soils and plant ecosystem, rather than using harder engineered solutions. SuDS systems copy natural systems, mimicking their behavior so that water is absorbed into the ground, evaporated or used up by plants. SuDS improve water quality downstream and help increase biodiversity.
In our increasingly variable climate, there is an urgent need to manage our areas to intercept water by improving the function of ecosystems and habitats within developments to buffer rain fall whilst providing amazing spaces for people to live. Effective design of SuDS systems can offer a multitude of benefits to the wider environment, socially culturally and economically.
TerrAffix Soil Solutions were invited by Richard Allen, CEO of Ecobunker (www. Ecobunker.co.uk) to trial some innovative products for the establishment of vegetation on steep, free-draining banks over sandy soil.
The golf course owners wanted to green up the slopes around the bunker edges and the reprofiled banks surrounding the carpark entrance.
The golf course’s proximity to the coast makes it a stunning venue for a game but it also means that the grounds are subjected to salty, windy and drying conditions. Such severe conditions make vegetation establishment difficult.
It was essential here to use a revegetation system which supports and protects the sown seed through the initial stages of growth while preventing soil loss or erosion.
TerrAffix-Hydrabase was applied using our bespoke hydroseeding equipment; we used a mix of native grasses recommended by Ecobunker to quickly establish a sward. We used a variety of additives in response to the particular ground conditions on the site, including a completely natural fertilizer, tackifier to prevent erosion and mycorrhizal fungi which support long term soil and plant health.
The vegetation quickly established itself within a few weeks of application.
TerrAffix Soil Solutions was invited by Murphy Rail to trial our re-vegetation system on a rail embankment that was proving particularly challenging.
The site was a steep slope of thick, cold clay sub-soil and it was susceptible to heavy run-off over the winter. Previous attempts at establishing vegetation had failed as this sort of soil can be a difficult material for new plants.
Clay can shrink and expand in response to heat and water and it can go from being very wet and cold to very dry.
These changes can sometimes happen quite quickly, making it difficult for plants to cope.
TerrAffix trial in background
To get plants to grow it is essential to provide the basis for life: moisture, sufficient organic matter to act as a soil-forming material, nutrients and a stable surface during germination.
Following the site survey we decided to use a two-stage revegetation system for the most effective results. We began with an application of TerrAffix-HydraSoil with a microbiological inoculant and a nutrient carrier. This mixture also helps to retain water within the developing root zone during the summer months.
We applied our own fully biodegradable tackifier formula which is composed of a mixture of natural, plant-based materials and sugars. No polyacrylamide was used, which is an everyday tackifier used in hydroseeding.
We then applied a coat of TerrAffix-HydraMulch with seed and natural plant nutrients. This application creates a stable surface on steep slopes, securing the seed in place through germination.
Vegetated soil on the railway embankment post treatment with TerrAffix-HydraSoil and TerrAffix-HydraMulch
We selected seeds from a mixture of fast-establishing species to get some initial cover as well as some deep rooting species. Deep rooted plants tend to be more resilient to drought and act as natural near-surface ground anchors.
The application was made in November which happened to coincide with above-average rainfall. Nevertheless the vegetation established successfully and created a robust, resilient sward.
A key material we use is biochar which is produced at our centre. Biochar not only confers a considerable advantage to plant growth but also sequesters atmospheric carbon dioxide.
Our products come with a carbon lock guarantee which can be accounted for within any corporate social responsibility targets.
Mine tailings with stream passing through
Green Solutions to Erosion and Mine Waste
The abandoned Nant y Mwyn lead mine lies in the valley of the Pen Cerrig Mwyn mountain and stretches to the banks of the Afon Tywi. In 1932 the mining company went bankrupt, leaving behind vast, steep-sided mounds of fine-grained and heavily polluted material.
The mine waste is too contaminated for anything to grow, and much of the site is bare.
With no vegetation to cover the soil and no roots to stabilise the surface the waste heaps are prone to severe erosion. As the tailings erode the material is deposited in rivers and pasture and causes significant contamination of the surrounding area.
TerrAffix have been working on a solution that is both cheap and effective and will vegetate mine sites such as Nant y Mwyn. The trials are being studied by Heather De-Quincey of Swansea University, who has a background in geochemistry.
Nant y Mwyn mine tailings and spoil heaps with the stream below
Extensive Pollution Impacts from Orphaned Mines
The waste from Nant y Mwyn impacts upon 65 km of waterways and causes environmental standard failures for zinc, copper, lead and cadmium.
Most mine reclamation strategies involve using machinery to re-profile the landscape before capping the waste with geotextiles and clay.
However, for orphaned mines with no owner liability, the cost of this process is prohibitively expensive for the government bodies with whom the responsibility falls.
Research into Solutions
TerrAffix have been sponsoring Heather’s PhD, developing and testing a low-cost green-engineering solution to reduce the erosion and the spread of pollution without the need for hard engineering.
This involves hydroseeding a biochar-enhanced, organic growing medium created from sustainable natural materials and seeding with a diverse acid and metal-tolerant selection of grasses that mimic the native community.
Nant y Mwyn mine tailings and spoil heaps with the stream below
The vegetation, which is rapid, immediately reduces erosion, and long term these plants will facilitate nutrient cycling and soil formation, both essential processes which initiate ecosystem complexity.
Green Long Term Solutions
The on-going work is helping us develop cheaper and more effective reclamation strategies for mines which have previously been too expensive to remediate, ultimately providing a low-cost and accessible solution to land contamination and erosion reduction.