Costs – the 5th pillar of SuDS   – Great blog shows how easily costs of SuDS are over-estimated.

The new 5 pillars. SuDS should be:

  1. much cheaper than conventional drainage, whilst (costs)
  2. attenuating storm-water (quantity)
  3. filtering at source (quality)
  4. providing beautiful spaces to relax (amenity) and
  5. supporting a wide range of local wildlife (biodiversity)

The challenge – a case study

2B Landscape consultancy Ltd ‘When we were asked to provide a planting plan for a University Hall of Residence, we suggested that SuDS should form part of the design brief.  The client agreed, and we produced a feasibility report and plan to show that the constrained site had more than enough space to develop a landscape-based sustainable drainage scheme.  “What about the costs?”, the client quite reasonably asked.  “Should be cheaper” we said.  “Let’s work with the project Quantity Surveyor (QS)”.

The QS made some assumptions based on our concept plan, and came back with a cost which was marginally less than the previously designed conventional drainage scheme (which had been based on a large attenuation tank).  Well, at least SuDS didn’t cost more – the client was happy.  When we looked at the cost breakdown for the SuDS proposal, we noticed some major items that did not need to be attached to it:

  • Soil strip and relaying over swales: wasn’t that going to be happening in the landscape areas anyway? Yes, agreed the QS, that is not additional to the SuDS scheme, it is part of the site earthworks. Omit!
  • £36k for connection of surface water drainage to the swales (36 gullies).  Not needed, the water just runs off the paths into the soft landscape.  Omit!
  • Cost of erosion control matting? About one-tenth what the QS had estimated.
  • Other fittings were substantially less than original estimate, when market tested.

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