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05Jun 2013
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Can we afford not to consider SuDS from the outset?

Anthony McCloy, McCloy Consulting

 

The assumption that SuDS are less affordable is one of the dogmas which have dogged the SuDS debate for a number of years now.

 

Unfortunately, to come up with a comparable cost estimates of SuDS schemes against traditional drainage; it is not a simple matter of comparing the cost of a meter length of swales vs. a meter length of pipework (some information is here).  Quantity Surveyors have regularly asked me in the past, if the use of permeable pavement could be reconsidered as it was much more expensive than blacktop, without so much as considering that the permeable pavement also provided both a conveyance and storage drainage function, and how this might reflect in the overall cost within the scheme. (None of us are perfect I suppose…).

 

Previous point aside, the cost of the drainage scheme will come down to how the scheme has been designed. Notably, the scheme will invariably change throughout of the course of design refinement, as we reassess and consider better or more innovative (and potentially more cost effective) ways of providing a drainage solution to meet the design brief. Therefore for the same scheme you could end up with multiple different costings depending on which version of the design evolution is costed.

 

Generally speaking whenever SuDS is considered from the outset of a project it will be cheaper than the traditional drainage equivalent. Drainage should influence the layout at concept stage, by identifying flow routes and potential locations for storage within multifunction space thus not requiring additional land take.

 

However, if the drainage design is left as an afterthought, as it has mostly been to date with traditional drainage design, then the chances of coming up with an affordable scheme are greatly reduced, but not necessarily eliminated.

 

The finishing and detailing used in SuDS schemes is important, given that the majority of SuDS are above ground. The outcome of downgrading the finishing is that the drainage will look cheap and poorly designed. The downgrading of finishing will only have a marginal impact on the cost of the scheme as the significant savings are to be gained through properly considered layout and effective use of space.

 

We are still awaiting guidance from Defra on the matter, but consideration of the evidence to date, and also applying some very inexpensive common sense, would suggest that a SuDS schemes will be more affordable.

 

As a final thought, most of the discussion to date has been around the tangible, i.e. the cost of installation and the cost of maintenance. Consideration also needs to be given to the non-tangible direct and in-direct benefits of SuDS, as a means of place making and the many other amenity benefits that they can bring. How these are monetised is a different matter, but should they be factored into the affordability equation, it is likely to turn the tide in favour of SuDS into a much more substantial wave.

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