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Hard vs Soft SuDS - weighing up the pros and cons

Government is not asleep to the threat of stormwater flooding and has, in the last six years, taken several steps towards addressing it, starting in 2002 with Approved Document H.

This changed the hierarchy of drainage and drainage design considerably and introduced the concept of Sustainable urban Drainage Solutions (SuDS).

In theory, SuDs employ a whole suite of techniques to effectively manage drainage at source. But in reality, SuDS are seen as swales and drainage ditches acting as storm water attenuation ponds. Development of them has been slow with water companies reluctant to adopt them and developers unwilling to waste valuable land installing them. The alternative is below ground storage based on modular tanks or large diameter pipes. Both have advantages and disadvantages:

Above Ground (Soft) SuDS

Pros

Ease of construction (generally only earthworks required)
Ease of access for maintenance
Can create a landscaped visual feature
Natural treatment
Encourages biodiversity
Lower upfront cost

Cons

High land take
Potential eyesore and health & safety risk if not maintained or abused. Can be abused by flytippers.
Site topography and conditions can limit functionality
Lack of designer and contractor expertise.
Not conducive for water reuse

Below Ground (Hard) SuDS

Pros

Minimises space required
Can use land above
Protected against misuse or vandalism
Can retrofit
Recognised design standards
Conducive to rainwater reuse

Cons

Water treatment for discharge into water courses requires ancillary components
Greater maintenance expertise required as they are confined spaces
Site conditions can limit functionality (e.g high water table level)
Higher initial cost

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