SUDS for Roads

The UK’s road network represents the country’s largest continuous impervious surface area .

SUDS impact

The principles of SUDS have been developing in the UK since the early 1990s, and have been enshrined in successive legislation since 2003 with the Water Framework Directive (WFD). But primarily, the focus has been on developments other than roads until comparatively recently.

However, roads are a major source of diffuse pollution – a key target of the WFD.  So pressure has increased to tackle both volume and water quality from poorly controlled runoff. The growing appreciation by Transport Scotland and the Highways Agency that SUDS measures can provide value for money solutions which can mitigate volume and improve quality of highway runoff has encouraged them to incorporate SUDS into highways planning.

Scottish focus

In Scotland, the Scottish Environmental Protection Agency (SEPA) has worked with the transportation and highways industry to produce a manual entitled SUDS for Roads in 2009 and revised in August 2010.

This offers a SUDS application overview, practical design and construction guidance and UK Roads Boards and the Environment Agency in England and Wales have also followed the development of the manual with interest. The Highways Agency for England and Wales also has its own water quality and drainage Guidelines.

Amongst other measures, including detailed matrices for assessing different roads and their needs, SUDS for Roads emphasises the necessity for attenuation storage, and a minimum of two levels of treatment of runoff water.

Engineered SUDS

The techniques discussed including filter strips, permeable paving and swales are ideal for new infrastructure, where there is room; however, the problems of land take are also acknowledged. Recent (2010) studies of actual projects have now indicated that engineered SUDS solutions can have a role in complementing and enhancing the purely natural methods in certain contexts, especially upgrading existing installations.