Bioretention System Engineers in Nature’s Way

Written by: , 8 May 2011

An innovative new sustainable drainage system, Hydro Filterra™, has been launched by Hydro International to introduce the pioneering principles of bioretention and biofiltration to the UK’s highways and car parks in an attractive, compact and predictable technology.

Hydro Filterra™ is a SUDS-compliant drainage unit which harnesses natural biological and chemical processes to combine stormwater control with treatment of pollutants and sediments, ideal for both retrofitting and new developments.

From the surface, the Hydro Filterra™ system looks like a tree box with suitable plants or a tree protruding through a decorative grating in a typical concrete slab at pavement level.  Stormwater runoff is channelled through a kerbside inlet into a concrete container underneath filled with a mulch, plant and soil filter medium.

“Often the most sustainable drainage solutions are those which engineer in nature’s way – combining the best of natural processes with a simple and practical technology,” said Alex Stephenson, Stormwater Director of Hydro International.  “Hydro Filterra™ provides filtration in an attractive unit that enhances the landscaping and amenity of a street scene, with the added advantage of keeping tree roots contained.

“Often, achieving SUDS-compliant filtration can require a treatment train solution with a range of drainage elements, each providing a level of treatment and targeting specific pollutants.  The beauty of Hydro Filterra™ is that as it operates through an array of physical, chemical and biological processes simultaneously to provide a mini-treatment train in a single device.”

Underneath the pavement, the Hydro Filterra™ system comprises a concrete container with a 75 mm mulch layer, 500-750 mm of unique soil filter medium, an observation/clean out pipe and an under drain system, which is connected to the surface water drain, infiltration or soakaway system.

Treated water can also be diverted into additional storage / infiltration systems using geocellular structures such as Hydro’s Stormcell® or the Stormbloc® systems.  An emergency overflow bypass facility is used for extreme events.

Filterra™ technology was pioneered in the US, where it has already achieved widespread acceptance and is nearing 4,000 installations.  It is approved as a stormwater management device for hard surface developments where planning permission requires the provision of surface water pollution control and has completed rigorous US product verification programmes

Filterra™ was developed as an engineered bioretention system to overcome the limitations of conventional bioretention and biofilter systems, due to their large footprint and lack of design predictability.  Hydro Filterra™ connects simply to drainage inlet and outlet systems, provides for ease of design against flow control and treatment parameters and performs consistently whatever the site characteristics.

Hydro Filterra™ requires 90-95% less land-take than traditional systems, with predictable soils that provide higher levels of treatment for Phosphorous and Nitrogen, two of the most environmentally damaging causes of nutrient pollution.

In the UK, stricter legislative requirements will place increased emphasis on the removal of oils, pollutants and sediments from surface water in future, driven by the European Water Framework Directive’s 2015 water quality objectives.

The implementation of the Water Environment and Water Services Act (Scotland), Flood and Water Management Act (England and Wales) and in particular the introduction of new National Standards for Sustainable  Drainage Systems (SUDS) by April 2012, are also likely to require developers and highways authorities to incorporate treatment elements in their SUDS systems.

Meanwhile current Department for Transport design guidance for highways authorities is encouraging a more integrated approach to improving urban street scenes with greater emphasis on landscaping and amenity.

For more information about the new Hydro Filterra™ Bioretention System, or any of Hydro’s storm and wastewater management systems, please call 01275 878371 or visit


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