What are Sustainable Drainage Systems?
Sustainable drainage systems (SuDS) are drainage solutions that provide an alternative to the direct channeling of surface water through networks of pipes and sewers to nearby watercourses. The use of Sustainable Drainage Systems can reduce the risks and impacts of surface water flooding, improve water quality, and enhance the amenity and biodiversity value of the environment. Furthermore, rising rates of population growth and urbanization and the impacts of climate change mean the need for sustainable natural management systems such as Sustainable Drainage Systems is likely to increase in the future.
How do Sustainable Drainage Systems work?
In natural environments, river levels are maintained by high rates of infiltration into soil and bedrock, and surface runoff is reduced due to high rates of interception and evaporation by vegetation. Denser vegetation also has a greater capacity to store rainwater, which further reduces risks associated with flooding.
In urban environments, impermeable surfaces such as concrete and tarmac can reduce natural infiltration to soil and bedrock. Instead, man-made channels such as pipes and culverts divert surface water to local water courses. This increased runoff can lead to downstream flooding and deterioration of water quality if foul sewers are overwhelmed by surface water.
What do Sustainable Drainage Systems look like?
Sustainable Drainage Systems aim to alleviate these problems by storing and filtering rainwater more effectively. Some techniques include:
Storing or re-using surface water by intercepting run-off water on roofs, leading to water storage and subsequent evapotranspiration e.g. green roofs.
Using retention systems to delay the discharge of surface water to watercourses, such as retention ponds or wetlands.
Improving water quality by using vegetated swales or filter trenches, which remove pollutants from surface water prior to discharge to watercourses or aquifers.
Permeable paving blocks, which have uneven edges that create gaps between the blocks, allow water to flow through them and into the ground below. Some examples of permeable paving are shown here:
The importance of ground properties
Underlying soil and rock conditions play an important role in determining the effectiveness of Sustainable Drainage Systems, as underlying ground conditions need to be permeable and free draining for many of these systems to operate effectively. Sands and gravels, for example, have high storage capacity for
groundwater, however, silts, clays, and igneous rocks have lower permeability and therefore offer lower storage capacity.
How do Urban Designers use Sustainable Drainage Systems?
Designers hoping to use Sustainable Drainage Systems on a development site need to be aware of several factors which can affect their suitability, for example, the existence of previous buildings and structures, details of the ground’s permeability, nearby flood risks or flood zones, and details of possible ground contamination. Expert consultation and the use of geological data and Geographical Information Systems can therefore be valuable tools in the design process which can help to avoid costly implications later in the development process.
With early thought, careful planning, and due diligence, Sustainable Drainage Systems can be incorporated into urban designs leading to an increase in the appeal of development and in benefits to both people and the environment.
Ar. Latika Gangadhar Ambekar
Visiting Faculty at Smt. K. L. Tiwari College of Architecture