Sustainable Urban Drainage Systems - SUDS

SUDS, or sustainable urban drainage systems are an alternative to the traditional approach of collecting stormwater in pipes and discharging it into treatment works or watercourses.

SUDS best practice limits the flow of rainwater which runs off a site or is piped away, protects local watercourses from the contamination carried in surface runoff, encourages natural groundwater recharge (where appropriate), and reduces the likelihood of downstream flooding.

Burdens Environmental recommend the following systems which can be used as stand alone solutions or (depending on requirements) combined to enable effective sustainable urban drainage.

• Rainwater Harvesting Systems
• Rainwater Soakaway Systems
• Rainwater Attenuation Systems

Building Regulations
The Building Regulations Approved Document H3, Rainwater Drainage, which came into effect on 1 April 2002, prioritises drainage requirements. In short, it requires that rainwater from the roof of a building or from a paved area may either be gathered for reuse or be discharged into one of the following, listed in order:

• an adequate soakaway or some other adequate infiltration system; or, where that is not reasonably practicable
• a watercourse; or, where that is not reasonably practicable
• a sewer

In other words, the traditionally preferred method of rainwater disposal, ie totally discharging to a sewer, may now only be considered after other forms of reuse or drainage have been considered. The Building Regulations also provide guidance on the construction of rainwater harvesting systems for the first time.

Environmental Guidelines
Stormwater runoff from impervious surfaces often carries a high pollutant load that has a detrimental effect on the bodies of water into which it discharges. Sediment has been identified as one of the most widespread pollutants impairing the water quality of rivers and streams. To mitigate the problem, planning and environmental guidelines such as PPG25 (Planning Policy Guidance No. 25) are becoming more stringent. Developers and authorities are required, through UK building regulations, to consider sustainable urban drainage systems as priority solutions rather than more conventional drainage systems.

Recent research shows that typically up to 80% of sediment; 60% of phosphorous and; 80% of nitrogen can be removed from rainwater through porous paving , and grass/gravel porous paving systems. This natural treatment provides the ideal opportunity for rainwater conservation and re-use for a variety of non-potable applications e.g. toilet/urinal flushing, irrigation, laundry, process water, vehicle washing, refrigeration, coolant use, etc.

Planning
Implementing SUDS contributes significantly towards achieving sustainable development. Many planning authorities will expect planning applications, whether outline or detailed, to demonstrate how a more sustainable approach to drainage is to be incorporated into development proposals. Planning authorities will set a limit to the rate of stormwater flow from a site via sewers as a condition of planning consent. In recognition of this, Local Plans increasingly state that all applications should, in the first instance, aim to incorporate SUDS into development proposals. SUDS are also considered suitable for mitigating adverse impacts and supporting water conservation objectives.

SUDS incorporate cost-effective techniques that are applicable to a wide range of schemes, from small developments to major residential, leisure, commercial or industrial operations with large roof areas and hardstanding. They can also be successfully retrofitted to existing developments. Planning policy guidance on development and flood risk emphasises the role of SUDS and introduces a general presumption that they will be used. As with other key considerations in the planning process - transport, landscape, heritage and nature conservation - incorporating SUDS needs to be considered early in the site evaluation and planning process, as well as at the detailed design stage.