Here, Dave Rudd, National Sales Director at Keyline Civils Specialist, provides an overview of the role of geotechnical products and solutions in SuDS, what is available and provides advice on selection of the correct products.
Flooding is a key issue in urbanised and developed areas due to the increased quantity of hard impermeable surfaces that cause fast rainwater run-off. With climate change already driving increasingly extreme weather in the UK, experts warn that flooding will only become worse in the coming years. Met Office figures show that since 1998, we have experienced six of the ten wettest years on record. In 2020, the UK saw total rainfall figures that were 14% above average including the wettest day (3rd October) since records began in 1891.
Sustainable Drainage Systems (SuDS) are key to counteracting this effect and as a result, are a core part of planning. The Flood and Water Management Act 2010 requires developments to utilise elements of a SuDS approach to reduce the flood risk.
Geotechnical products can help developers meet the principles of SuDS in a number of ways, including allowing water to soak into the ground (infiltration), slowing the discharge of rainwater (attenuation) and reducing the pollution in runoff water to protect and enhance water quality.
Firstly, porous and permeable pavements provide an excellent option for reducing the number of impermeable surfaces and therefore slowing runoff and helping to prevent flooding. Many of these systems are suitable for a wide range of applications including residential streets, parking areas, pedestrian zones and driveways. To ensure the permeable pavement remains stable over a range of project conditions, the inclusion of a stabilisation geogrid within the granular foundation component of the pavement will maintain, or even increase the trafficking capacity of the finished pavement, allowing it to operate effectively. Geotextile membranes can also be used to maintain the stability of the ground by ensuring separation of different construction substrates while still allowing water to pass through.
Additionally, there are specially engineered membranes that also act as a filter to capture and degrade pollution carried by the water. The fibres used in these geotextiles encourage a biofilm of microbes to develop that biodegrade oils and other pollutants. For example, some high quality membranes have the capacity to consume as much as 400g of hydrocarbons per square metre per year. Other, non-degradable substances are retained by the membrane to prevent pollution entering water courses.
Alternatively, it may be necessary to prevent water reaching deeper layers of substrate, especially where this contains contaminated soils that would damage rather than enhance the quality of the water. In these cases, durable, impermeable geotextile membranes can allow the complete separation of the contaminated material and the SuDS system above.
Furthermore, geotechnical products can also be used to create rainwater storage features that additionally help to enhance the biodiversity of the area. Using the correct membrane, retention ponds can be easily created to allow stormwater to be held and released slowly. If designed correctly these ponds can provide much needed habitats for wildlife in urban areas.
There are a wide range of geotechnical products and solutions available, all with varying properties and levels of performance. It is essential to select a product for each area of the project that meets the specific requirements of that application and is fully compatible with the chosen drainage system.
It is also important to choose high quality products that will last. Standards such as ISO 9001 can help identify manufacturers that have made a commitment to quality. In addition, it is recommended that developers seek products that have been tested to the specific industry standards such as ISO 10319, ISO 12236, EN 12224 and EN 12225 that respectively measure the tensile strength, puncture resistance, weathering and microbiological resistance of geotextiles.
Finally, due to the importance and complexity of choosing the right solution it is beneficial for developers to partner with a specialist merchant. This allows access to expert advice on the best options to meet project requirements. Experience and in-depth product knowledge may also allow the opportunity for value engineering to reduce costs without impacting performance.