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Sustainable Urban Drainage Systems
It rains a lot in Britain. Each new development must make provision for the surface water runoff to be drained from the site.
Draining surface water from urban areas using conventional positive drainage techniques has led to problems. These include:
The challenge is to drain the surface water runoff without causing flooding or pollution and without reducing the amenity value or the local biodiversity of the site. SUDS drainage design requires that the rate and volume of runoff is reduced to minimise the impact on receiving waters or drainage systems downstream. Diffuse pollution can also be reduces by the techniques of SUDS.
Sustainable development is a journey and not a destination. Implementation of sustainable urban drainage systems will contribute to sustainable development.
Why do we need SUDS?
Sustainable Urban Drainage Systems provide a way of solving these problems
through the use of drainage methods inspired by natural processes. They take
account of surface runoff quantity and water quality equally with the amenity
and ecological value of water in the built environment. They can also promote
the involvement of all stakeholders in making decisions about drainage and
the environment, thus developing community awareness and ownership.
There are many techniques for managing surface water in a more sustainable manner. The main aim of SUDS is to promote the control of runoff and pollution as close to the source as possible. Some of the techniques used, such as soakaways, have been used for many years. Other techniques, such as porous pavements and reed beds are more recent innovations.
SUDS can attenuate flows thereby reducing the risk of flooding and also provide time for the natural processes of sedimentation, filtration and biodegradation to occur. This reduces the pollutant load in the surface water runoff.
In addition, SUDS can be designed to fit into their environmental setting, adding considerably to local amenity and biodiversity.
Although SUDS are drainage devices that rely on natural processes, SUDS must be designed, built and maintained in the context of the development control system in force. Developers must arrange for their drainage systems to be adopted by a statutory body, usually the drainage authority, in order to be able to sell their houses.
Unfortunately, there is little agreement between the various statutory authorities in standards for adoption. Sewers for Adoption requires that the sewerage system should not surcharge in a 30-year event. Flood protection if routinely being demanded for a 100 or even 200 year event. The adoptable sewers would not convey this flow to the attenuation devices.
SUDS principals require the reduction of volume as well as flow from the drainage system, typically to less than the undeveloped runoff. This requires infiltration, evaporation or evapo-transpiration. Adopting authorities are opposing open ponds and are requiring tank sewers for attenuation, which cannot reduce volume of discharge.
There is little agreement on the adoption of porous pavements, and householders are reluctant to accept the long term maintenance of structures away from their properties.
Proper design of drainage systems can provide major benefits to the environment, and the reduction of flooding, but not until agreement is reached on long term maintenance.
Hydraulic
Modelling
PPG25 implementation article
