Sustainable Drainage Systems

SUDS (Sustainable Drainage Systems)

SUDS (Sustainable drainage systems or sustainable urban drainage systems) are composed of a combination of management procedures and control structures designed to drain surface water. The successful drainage of surface water is achieved in a more sustainable way than conventional techniques.

The overlying idea of SUDS systems is to consider the aspects of water quality, quantity of water reserves and associated amenity issues within the urban environment. Addressing surface water run-off following rainfall, is a key element to these issues. Conventional drainage systems work on the principal of quickly removing surface water from urban areas (usually solely by drainage pipes) to reduce the risk of flooding occurring within the locality, but they have little regard for quality and amenity issues. Conventional methods greatly disrupt natural water flow patterns and are not considered to be sustainable.

The Idea

SUDS systems enable the careful management of surface water run-off flow rates. This can reduce the impact of flooding resulting from increased surface water run-off rates typically associated with the widespread usage of impermeable surfaces within urbanised areas. Systems can store water and effectively restore the sites pre-development surface run off characteristics. SUDS systems are designed to improve water quality and encourage recharge (where required) by allowing rainfall or surface run-off water to enter the SUDS system as soon as possible following rainfall. If the water enters the system at an early stage the risk of contaminants and particulates being picked up during surface run off are reduced and water quality is preserved. Systems can also be designed to protect water from point source pollution, such as accidental hydrocarbon spills within car park areas or known contaminated sites.

SUDS systems can be designed to increase the ground water recharge of natural soils by detaining water within channels or chamber features to promote increased infiltration levels.

Within urban areas, the need for amenity facilities and recreational areas can be met with the integrated use of SUDS systems. The community environment can be improved with the introduction of urban water ways or ponds as part of a SUDS system allowing a range of wildlife and habit to be established.

Building regulations (Part H - Drainage and waste disposal) require the first choice method for surface water disposal to be via infiltration drainage methods. As a result infiltration drainage methods such as soakaways and filter drains should be considered for usage where possible.

System Components

SUDS systems can be made up of any number of different water management features to enable infiltration and water quality improvement, where required.

Typical systems components are:

• Permeable surfaces:
  These allow surface water ingress through voids in their surface, but are constructed of impervious material. Water is stored and transported within the underlying sub-base material.
  • Concrete block paving (laid dry or with sand)
  • Specialist permeable paving blocks
  • Permeable pavements
  • Reinforced grass
  • Gravelled areas
• Filter strips:
  These are vegetated surfaces that receive and slow down surface water run-off and allow particulate removal and water infiltration.
• Swales:
  These are vegetated shallow channels that slow down and receive surface water run off and allow particulate removal and water infiltration.
• Filter and infiltration trenches (French drains):
  Trenches lined filled with a permeable material (crushed rock), sometimes incorporating perforated pipe to transport and store water. The permeable material acts as a filter and removes sediment from the water. A permeable geo-textile membrane may be used to line the trench to aid sediment filtering.
• Soakaways:
  This is a sub-surface chamber lined with a geo-textile membrane and filled with crushed rock to store and encourage infiltration of storm water by maximising the surface area of natural soils in contact with the water. The geo-textile membrane filters sediment from the water.
• Underground Storage Systems (Storm cells):
  This is an underground chamber lined with modular durable plastic cages (similar in appearance to milk crates), which supports the excavation sides. The cages interconnect and allow fast construction, compared to reinforced concrete structures. An impermeable geo-membrane is used to encapsulate the outer surface of the assembled cages to retain water within the structure. Water can be held and released at a set rate to prevent flooding. A permeable geo-textile can be used in place of a geo-membrane to create a soakaway system, where water is filtered by the geo-textile before infiltrating into the natural soils.
• Basins and ponds:
  Surface excavations designed to retain or store water and promote infiltration following a storm event. They can be used to allow settlement of suspended solids and can be used in conjunction with reeds to remove pollutants from the water, prior to controlled discharge into water courses or infiltration to the natural soils. Biological activity within a pond environment can also treat and remove contaminants within the water.

Further guidance on SUDS can be found at:

CIRIA (Construction Industry Research and Information Association)