The flagship for sustainably-designed drainage

With recent focus on flooding and the increased risk that can be caused by urbanised areas, there is increasing pressure for sustainably-designed drainage to be implemented in new developments. Indeed an important interim conclusion of the Pitt Review of the July 2007 floods is that the automatic right to connect surface water drainage from new developments to the sewerage system should be removed.

Perhaps not surprisingly, environmental organisations often lead the push for more sustainable drainage. At Stamford Brook, near Altrincham, the National Trust sold 28 hectares of land (part of the Dunham Massey Estate) for a major housing development by Redrow Homes and Bryant Homes.

A condition of this sale was that the development must implement a longstanding plan to restore Sinderland Brook, the canalised stream that runs through the site and that a Sustainable Urban Drainage System (SUDS) should be incorporated.

Hydrological consultants Haycock Associates Limited were brought in by the Trust to design and implement the connected river restoration and drainage schemes. The SUDS comprise a series of swales and storage basins designed to enhance ecology and increase amenity value, whilst ensuring that surface water runoff from the development into Sinderland Brook does not exceed that of a greenfield site.

Meanwhile the wider, shallower river floodplain that was created was unusual in increasing the level of flood protection both to the existing housing and the new development, whilst also being more “natural” – the scheme won the recent Waterways Renaissance Awards. This provides a contrast to the common assumption of flood protection being achieved through more engineered control of drainage and rivers.

The developers were initially sceptical of the benefits of either scheme but with the successful increase in aesthetic and recreational value, the homes in the later part of the development were repositioned to face the river, as those with a view of the scheme achieved substantially greater prices than they had predicted.

The project has therefore become a flagship illustrating that managing drainage and rivers in a naturalised manner can benefit developers, residents, and wildlife alike, rather than seeing these as competing interests.

More information: www.haycock-associaties.co.uk

A pervious alternative to hard surface drainage

More residential and commercial development means more hard-standing impermeable surfaces, less ground where natural drainage is still possible and more pressure on man-made drainage. But one solution is the OSMA AquaGrid pervious paving system offering an alternative way to manage rain and surface water drainage.

There is a solution for both light to medium and heavily trafficked areas such as open car parking and access roads and for verge reinforcement and landscaped areas.

The system is quick and easy to install. It comes in lightweight interlocking square sections of recycled plastic, designed to receive pervious infill material for surface water drainage.

The 500 x 500mm units are secured by pins to ensure full system stability and integrity so that, once assembled, it is extremely strong and can withstand vehicle traffic and parking.

There are two versions. AquaGrid 50 is a 50mm deep version and AquaGrid 75 is a 75mm deep version.

The former is suitable for gravel and landscape environments with light to heavy traffic.

The latter is recommended for areas of regular heavy traffic loading or where premium grass quality is of the highest priority.

The 75mm version includes features such as lateral arches to optimise grass root growth and protection.

If you need additional selection advice, Wavin Plastics can advise on the suitability of each version depending on the application. Wavin additionally tests every AquaGrid unit for strength, loading and durability.

Both versions of AquaGrid are suitable for grass, soil or gravel infill. White marker blocks can be supplied to denote parking spaces. When assembled, both products allow lateral flow and offer up to 90% of their surface area for water permeation through the chosen pervious infill.

The system can be used to drain captured rainfall and stormwater either into the underlying ground or into an underground attenuation structure.

By contributing to sustainable drainage systems in this way, the AquaGrid supports the aims of Part H of the Building Regulations.

More information: www.wavin.com