What are Sustainable Drainage Systems?

Sustainable Drainage Systems (SuDS) are not new. They are, quite simply, nature’s way of dealing with rainfall.

At its simplest, rain falling on the land may evaporate or be absorbed into the soil, nourishing the natural habitat. Otherwise, it flows overland into ponds, ditches, watercourses and rivers, helping to sustain life by replenishing water resources.

It is only recently that the balance of this natural water cycle has been disrupted. Modern urban development with its houses, roads and other impermeable surfaces has increasingly altered the way that rainwater finds its way into our soils, rivers and streams. Surface water has for many years been collected and piped directly into our ditches and rivers. Conveying water away as quickly as possible from a development may adequately protect the immediate development from flooding but increases the risk of flooding occurring downstream. This unsustainable approach to surface water drainage, together with the potential effects of a changing climate, has contributed to some very serious consequences on life, property and the environment – as evidenced by the disastrous flooding experienced throughout the UK during the summer of 2007. 

A return to more natural, sustainable methods of dealing with surface water from development has benefits for:

  • Water quality – SuDS can help prevent and treat pollution in surface water runoff, protecting and enhancing the environment and contributing towards Water Framework Directive objectives.
  • Amenity – SuDS can have visual, recreational and sociological benefits for the community.
  • Biodiversity – SuDS can provide the opportunity to create and improve habitats for wildlife, enhancing biodiversity.

The Essex SuDS Design Guide (2016) forms the local standards for Essex and, together with the National Standards, strongly promotes the use of SuDS, which help to reduce surface water runoff and mitigate flood risk.

The National Planning Policy Framework (NPPF) provides support for decision-making in relation to SuDS through two key paragraphs:  

Paragraph 103: When determining planning applications, local planning authorities should ensure flood risk is not increased elsewhere and only consider development appropriate in areas at risk of flooding where, informed by a site-specific flood risk assessment following the Sequential Test, and if required the Exception Test, it can be demonstrated that:

  • within the site, the most vulnerable development is located in areas of lowest flood risk unless there are overriding reasons to prefer a different location; and
  • development is appropriately flood resilient and resistant, including safe access and escape routes where required, and that any residual risk can be safely managed, including by emergency planning; and it gives priority to the use of sustainable drainage systems.

A site-specific flood risk assessment is required for proposals of 1 hectare or greater in Flood Zone 1; all proposals for new development (including minor development and change of use) in Flood Zones 2 and 3, or in an area within Flood Zone 1 which has critical drainage problems (as notified to the local planning authority by the Environment Agency); and where proposed development or a change of use to a more vulnerable class may be subject to other sources of flooding.

Paragraph 109: The planning system should contribute to and enhance the natural and local environment by: …

  • preventing both new and existing development from contributing to or being put at unacceptable risk from, or being adversely affected by unacceptable levels of soil, air, water or noise pollution or land instability.

Page updated: 29/07/2019

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