SUDS

Sustainable Urban Drainage Systems

Overview of the numbers and types of SUDS

Background to SUDS

The concept of SUDS has been brought about by encouraging a radical new way of thinking about urban drainage systems as epitomised by the Quality - Quantity - Amenity triangle in figure 1.

Figure 1             The SUDS Triangle

The concept of SUDS (initially called BMPs) was identified as being the key means of addressing these problems of urban pollution.   In addition, SUDS happily meet the principal objective of the Rio Earth Summit's Local Agenda 21 ( ..think global act local) .   The principle of dealing with surface water runoff at source has now been taken to heart in the development and redevelopment of surface runoff systems.   As a result, by early 2001, a wide range of SUDS systems had been installed in Scotland.

SUDS and the Treatment Train

The Treatment Train (figure) has been developed to give a rationale for the development of SUDS drainage systems at a variety of scales.   It is a hierarchy which to be tailored to suit the size and the complexity of the area being drained.   The full hierarchy (with good housekeeping as an essential addition) has principally been adopted for larger developments by major developers who have independent site supervision.   A major site will have a range of integrated surface water drainage components.   Retention ponds and wetlands are the major regional treatment facilities while detention basins, treatment swales and infiltration systems are the principal forms of site control.   Source controls (e.g. water butts; disconnection of roof drainage, soakaways) may or may not be encouraged within each sub-site a development and depending on local conditions.  

Figure 4             The Treatment Train

Many developers will not wish to follow the management hierarchy to such detail, nor indeed will it be appropriate in some cases.   In acknowledgement of this, the design of a SUDS system is mainly directed towards flow attenuation, most of which is provided by site controls, with regional ponds providing surface water treatment where needed.

Developers require a quick to understand means of application of the treatment train and this is given in table 1 which expresses the treatment train in an alternative manner.   Good housekeeping, in the form of pollution prevention is always required.

Residential sites are the least likely to cause severe pollution, and the developer can select from the full range of SUDS system, although some devices would be over-elaborate for small sites.   Residential sites require only the first level of treatment.

Non-residential sites include shopping areas with their car parks, and larger housing estates which have access roads and bus stops etc.   These require the first and second levels of treatment.

Industrial Sites are where manufacturing processes are carried out and there is the potential for spillage of chemicals.   This category also applies to trunk roads and to locations such as bus garages.   Containment of pollutants is also needed for industrial sites.

Unfortunately it is not possible to apply rigid rules for the numbers of houses or the area of the development since the level of treatment is much more likely to depend on the potential for the production of pollution and the sensitivity of the receiving water.   For example, a small housing development by the sea would require a different level of treatment from one draining to a small eutrophic watercourse.