SuDS: The Scottish Experience
In many ways, the development and application of sustainable drainage systems (SuDS) in Scotland has led the way for the rest of the UK, with enabling legislation in place at an earlier stage than in England and Wales.
In 2003, the Water Environment and Water Services (Scotland) Act was implemented to deliver the requirements of the EU Water Framework Directive. This was followed in 2005 by the Water Environment (Controlled Activities) Regulations which imposed controls on abstractions and river impoundments, in particular.
The statutory agency which is empowered to implement and operate under these regulations is the Scottish Environmental Protection Agency (SEPA); SEPA works closely with Scottish Water (SW). Their work is also supported by SNIFFER (Scotland and Northern Ireland Forum For Environmental Research) which provides flood risk related and integrated water resource management research.
Sewers for Scotland 2nd edition was published in November 2007 to take SUDS into account as these systems may be vested by SW.
SuDS principles
The use of SuDS is integral to regulation in Scotland. SEPA requires that all new construction developments (except for single dwellings, or where discharge is directly into coastal waters) incorporate effective, appropriate SuDS, and developers and SW are encouraged to consult together with SEPA at very early stages in the planning process.
Treatment train
SEPA has defined SuDS as mimicry of natural drainage systems to preserve water quality, water quantity and amenity/biodiversity. It aims to do this through the SUDS Treatment Train, a four stage process of best practices. The practices comprise: good housekeeping; source controls; site controls; and regional controls. These aim to reduce or eliminate pollutants, and control runoff, at each stage in succession until the water reaches the watercourse.
Included in the treatment train facilities (SEPA refer to CIRIA697 for design issues. They don’t have their own rules) by SEPA are permeable surfaces, filter strips, trenches, swales, detention basins, ponds, underground storage and wetlands. They also mention that other facilities exist which include hydraulic controls and silt traps, as well as those which remove specific pollutants from the water.
Natural and supplemented engineering
SEPA encourages the incorporation of natural facilities wherever possible as it considers that these enhance the amenity and biodiversity value. However, there are many sites where site specific constraints and economics favour the use of mixed natural and engineered volume and quality control techniques.
SuDS has become standard practice in Scotland, with a survey by SNIFFER listing over 700 sites and nearly 4,000 installed systems.