Infrastructure in 2014: Adopting a long term solution
How confident are you that your sustainable drainage system (SuDS) will be accepted by a SuDS Approving Body (SAB)?
It is an important question because the Flood & Water Management Act 2010 requires a SAB to approve a scheme before construction can commence. Without approval, a scheme cannot go ahead.
SuDS schemes are designed to mimic the natural drainage characteristics of the land by dealing with rain where it lands through the use of engineered or landscaped features.
These limit the amount of run-off and prevent flooding. By contrast, conventional drainage solutions are designed to carry rainwater run-off from developments to an outfall as quickly as possible.
This can overwhelm the outfall, with large volumes of additional water inundating the surrounding land and watercourses causing flooding.
There are two main categories of SuDS features: soft and hard. Soft SuDS are usually landscaped, vegetated features including swales and detention ponds. Hard SuDS include proprietary engineered precast concrete soakaways and attenuation tanks. Many schemes will feature a combination of hard and soft SuDS solutions.
Regardless of the types of solution, once a scheme has been approved, the SAB authority will automatically adopt the SuDS system on completion of the development. This will put the authority in charge of a substantial, growing asset base.
With this in mind, it is essential that the long term maintenance of soft and hard features is considered. I believe that the situation is comparable to the average service life requirement for an adopted sewer - estimated at 800 years in the December 2011 Department for Environment, Food and Rural Affairs White Paper “Water for Life”.
The SAB authority will be responsible for the operation and maintenance of the SuDS system, which must perform effectively over the life of the development. It is therefore reasonable to suggest that the average lifespan of a SuDS solution will be centuries.
For hard SuDS features, one way of providing product assurance is to use a traditional solution, such as precast concrete, because there is a vast amount of experience and knowledge relating to the long term performance of this material.
Environmental impacts are also important when considering SuDS in a broader sustainability context.
The Concrete Pipeline Systems Association has invested in independently certified research to assess the carbon footprint of precast concrete components. This resulting report demonstrates that concrete components can have up to 35% lower embodied carbon when compared to plastic. However, embodied carbon (and other environmental impacts) is not typically part of the recognised SuDS design criteria.
A truly “sustainable” drainage system must surely provide the best combination of long term functional performance, as defined by the SuDS philosophy, plus the lowest sum of all environmental impacts over the lifetime of the asset.
- Stuart Crisp is the Concrete Pipeline Systems Association’s business development director