Background

Sustainable drainage is a concept that includes long term environmental and social factors in decisions about drainage. It takes account of the quantity and quality of runoff, and the amenity value of surface water in the urban environment. Many existing urban drainage systems can cause problems of flooding, pollution or damage to the environment and are not proving to be sustainable. Traditionally, these systems are designed to convey surface water run-off from developed sites as quickly as possible with little consideration of the effects downstream.

Sustainable Drainage Systems (SuDS) provide an integrated approach to surface water design problems, which consider quality, quantity and amenity aspects equally. This integrated approach is commonly represented by the SuDS triangle.

The term SuDS covers a wide range of urban drainage facilities from end of pipe facilities such as wetlands or retention ponds, to source control systems such as soakaways, infiltration trenches and basins, swales and permeable surfaces.

A UK SuDS database has been set up to gather knowledge and experience of SuDS sites in the UK and to disseminate this information across the industry. Click here to access this website.

Why SuDS?

SuDS are more sustainable than conventional drainage systems because they are designed to manage flow rates, protect or enhance the water quality and are sympathetic to the environmental setting and the needs of the local community by controlling rainwater at source (source control) or attenuating flows and regulating discharges to greenfield run-off.

It is now widely accepted that the drainage of developed areas by conventional piped systems is not sustainable. These systems are often designed to remove surface water run-off from developed areas as quickly as possible with little regard for the drainage regime downstream or the quality of the water. In dry periods when flows are low, these systems can often silt up, causing a problem when the next storm arrives. This contributes to flooding and pollution of watercourses. Also, by diverting rainfall to piped systems, the amount of water infiltrating the ground is reduced, depleting ground water and reducing flows in watercourses in dry weather.

In Wales the impact of flooding is well known, with approximately 12% of the housing stock at risk from flooding. Recent flood events have only underlined the problem, and the predictions for future climate change and the need to meet the demand for housing means that the issues must be confronted. SuDS offer the opportunity to manage surface water, reducing the impact on flooding and pollution.

The SuDS Working Party for Wales has been set up to provide a focus for SuDS implementation in Wales and is chaired by the Environment Agency Wales. The Working Party is made up of all the relevant stakeholders who are working together to actively promote the use of SuDS on developments in Wales. The issues of adoption and maintenance of SuDS systems are complex, but guidance is being developed to help developers and designers through the maze.