CONCERNS over climate change and a number of major flood events across the whole country have all meant making Sustainable Drainage Systems (SUDS) a part of our every day life.

To the outside observer, SUDS have few flaws. Easy to access surface features that will manage water run-off from all types of development providing benefits to the community, attenuating run off to reduce flooding and managing pollution by treating run off and trapping silts. But, as usual, nothing comes without a cost - or in the case of SUDS, many costs if not managed properly during the design stage.

Ascertaining an accurate lifetime cost for any SUDS system can be a tricky business. The construction, clearance and material elements of SUDS are all easily quantifiable and, at face value, can in some cases be a cheaper option than traditional drainage systems. However, the uncertainty over the design lives of SUDS means that predicting and planning for any system’s failure causes significant difficulties, particularly for the adopting authority.

When SUDS fail, it is a long road to recovery. And, of course how easy SUDS long term management is, also depends on their design. All schemes will mitigate received waters, but how well? Has appropriate consideration been given to extreme weather? In the age of climate change, has the design considered prolonged wet weather or fierce storms?

Often the consequence of SUDS failure does not have an immediate impact on the site generating the run off so perhaps the incentive for a more expensive quality design isn’t always there. Those adopting authorities that have had to deal with the legacy of poor SUDS design and the resulting offsite pollution will know that when SUDS fail, it is a long road to recovery.

Lincolnshire County Council is one authority that has been affected. The organisation’s area highways manager, Mark Welsh, explained why the practicalities of SUDS design matter to him: “For me there are two main issues relating to SUDS; practicality and liability. In terms of practicality, SUDS are principally about reducing and delaying runoff from impermeable areas, and people talk of management train principles. Hydraulic design of developments, particularly taking account of extreme weather, where SUDS are to be used, is critical. The County Council, therefore, considers flood path planning to be critical when SUDS are used; where does the water go when the systems are beaten? Developers must demonstrate that property is not flooded,” he said.

With regard to liability: In May to August 2003, the National SUDS Working Group undertook an extensive consultation exercise on the ‘Framework for Sustainable Drainage Systems in England and Wales’.
The results stated that, from the 1,200 copies of the document sent out, the most frequently raised issues revolved around maintenance ownership and funding.

Although respondents did not spontaneously single out legislation as a key issue, it was certainly mentioned throughout the responses and viewed as intrinsically linked with ownership funding and maintenance, since respondents felt there had to be legislation to ensure that these aspects were dealt with adequately.

But before any of us can judge the SUDS design managers too harshly, we should consider what they’re up against. There are a huge number of variables that need to be considered in SUDS design and construction. From topographic constraints, to the size of development, to soil type and density of planting, all design factors need to be planned to achieve the lowest long term maintenance cost, not an easy balancing act. Local authority engineers today are picking up the costs of resolving problems created by poor decisions made by previous generations. It is not surprising, therefore, that they are concerned as to whom will be responsible for maintaining SUDS in 10, 20, 30 years and beyond.

Although designers and developers have to consider SUDS provision on all sites, there is currently no legal requirement on any one statutory organisation to take responsibility for their upkeep and repair. The highway authority will maintain traditional piped highway drainage and the sewerage undertaker will adopt piped
attenuation facilities but both are reluctant and in most cases will refuse to take on the responsibility for above ground provision, such as ponds and swales.

This reluctance to adopt above ground features is often overcome by placing the responsibility for future maintenance in the hands of an independent management company. However, there are growing concerns as to the effectiveness of these arrangements. In particular, will the company still be in existence in say 30 years time when the structure needs to be repaired? Or worse still, is it possible for a company based many miles from the site to react efficiently to an immediate and real risk of flooding due to the failure of the structure? Will the management company even be aware that they are responsible for a pond 100 miles away that they have had no cause to visit in the last 30 years?

Beal Homes has recently undertaken a 35-unit development in Stallingborough, North East Lincolnshire, with no capacity in the public surface water sewer and the usual Environment Agency restrictions, of discharge equivalent to agricultural runoff, with a hilly topography. The contractor decided on two large diameter online storage tanks with flow controls to attenuate discharge to five litres a second. As with most modern housing developments the type of road design preferred by the planning authority was not conducive to laying large diameter pipes whilst complying with Sewers For Adoption requirement that the pipework be a minimum 1m from the kerb line.

Working with the architect and planners the layout was amended in order that the attenuation tanks could be provided. The capital costs of the below ground SUDS was more expensive than if the flows had been attenuated within a pond, but no building land was lost.

When the value of the houses that would have needed to be removed was taken in to account the real costs of this solution were significantly less. As the tanks form an integral part of the sewer system they will be adopted by the sewerage undertaker ensuring their long-term maintenance.

Above ground SUDS can be an attractive feature of any development, residential or commercial. Ecologically, we could make SUDS excel, if people wanted to invest that little bit more.

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