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Selection

Sustainable drainage systems are designed using the same underlying principles of hydrology and hydraulics as conventional drainage systems, but applying them in a different way. Alongside the purely technical issues are wider considerations of amenity and environmental enhancement.

Principles

When selecting SUDS it is important to consider quality, quantity and amenity design criteria equally. There will not be a single "correct" answer: several options may meet the design criteria, and judgement will be needed.

Selection and design of SUDS are multi-disciplinary processes. Unlike conventional drainage systems, factors that influence the final choice will include planning, water quality, water resource, architectural and landscape requirements.

The Selection Tool

Once an initial assessment of the site has been made and the design strategies for the drainage system have been agreed, drainage techniques can be selected.

The selection tool is based on the surface water management train and is designed to lead the designers through the selection process in accordance with the principles that:

Drainage techniques will be used in series to meet the design criteria

Drainage techniques at the top of the management train are generally to be preferred to those further downstream

There is no single correct solution; selection may be the result of factors external to the normal remit of drainage designers

The drainage system should be inspired by the original drainage pattern.

The process is cyclical, and various factors have to be considered in increasing detail as a final solution is approached. Some of the additional factors that may influence the choice are discussed later in this section.

The suggested route to select a drainage system is not rigorous; value judgements have to be given and subjective assessments made of the capabilities of the site. Do not approach the selection process as a linear path through the flowchart – the decisions required need to be put in a wider context than just the pure technical details. In some cases the decision to use ponds for environmental enhancement or increasing property values may override other considerations.

Source control is preferred over controls elsewhere in the management train as it:

Follows the natural drainage pattern
Assigns the management of surface water to those responsible for the runoff
Prevents problems arising rather than trying to mitigate them.

An interactive selection tool will be added to the website shortly!

(August 2002)

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