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WET News WET News It's raining SuDS • Proprietary solutions should be considered as part of any sustainable drainage system. The CPSA's Stuart Crisp explains. W e have entered a brave new world. In April the planning regula- tions in England and Wales were amended to 'expect' Sus- tainable Drainage Systems (SuDS) to be included in all major new commercial develop- ments and housing develop- ments of ten or more homes in order to gain planning permis- sion. Since then the Welsh gov- ernment has published a con- sultation document whilst in England there are less visible signs of progress. Under the new rules, a SuDS solution to surface water run-off is managed using land- scaped and engineered under- ground solutions. It is about dealing with rain where it falls, which is in contrast to conven- tional drainage solutions that are designed to carry run-off from a development to an outfall as quickly as possible. Design option For drainage solutions to be truly sustainable they must be the most appropriate, which means making the most of both hard and so… SuDS solutions. So… SuDS are usually landscaped, vegetated features including swales and detention ponds. Hard SuDS include proprietary engineered precast concrete soakaways, atten- uation tanks and treatment chambers. So… SuDS options can achieve excellent results and provide a useful starting point when considering design options. However, vegetated SuDS solutions can take up large areas of land, which may be impractical or may simply reduce the potential profit from a site to the point where its development is no longer commercially attractive. By contrast, proprietary solutions such as precast concrete underground storage, flow control and attenuation systems can all make a contribution to ameliorating run-off while not using valuable land. Achieving the best and most appropriate SuDS solution will o…en involve a combination of both hard and so… solutions. SuDS currently only applies to medium- and large-scale developments, those of ten or more homes and major commercial developments, to avoid excessive burdens on business. However, is there nothing to stop a developer building in phases of up to nine homes to avoid breaching this minimum? Similarly, if there were a lot of small developments in an area the cumulative effect of run-off from all of these may not be addressed. While the current minimum of ten homes is a practical starting point, for SuDs to be to be most effective the threshold will need to be reduced over time. Under the arrangements that came into effect in April, local planning authorities should now consult the lead local flood authority on the management of surface water for major developments on matters relating to planning and discharges to satisfy themselves that a proposed development's SuDS solution is technically compliant and appropriate under the approval process according to the National Planning Policy Framework Practice Guide issued by DCLG and the non- statutory technical standards published by Defra which defines runoff flows and volumes. Guidance on non- statutory technical standards is awaited. Piecemeal approach The lead local flood authority should be able to assess the risk of surface water flooding across planning boundaries to help reduce the likelihood of flooding. As part of the approval process, it is the responsibility of the planning authority to ensure that appropriate SuDS maintenance is put in place. This arrangement should help overcome concerns about the capacity and technical expertise of local planning OCTOber 2015 WET NEWS 9 authorities to deal with drainage issues for major developments. That said, this is a piecemeal approach with individual local authorities consulting with individual lead local flood authorities, which could result in inconsistencies nationally that may lead to disputes between developers and local authorities. The ongoing maintenance of SuDS is also a concern under the new rules despite the SuDS approval process requiring local authorities to ensure developers have economically proportionate arrangements in place for maintenance over the lifetime of a scheme. Maintenance could be carried out by a local water authority or by a private contractor with arrangements decided on a case by case basis, which means there will be much less certainty over who actually has responsibility for a scheme's maintenance. And, if no agreement is reached, there is a danger that plans could be shelved. The new rules also give developers and planners an opt-out clause because SuDS do not have to be provided if they can be "demonstrated to be inappropriate". This could allow planners to choose not to insist on SuDS when the costs associated with them are deemed to affect the viability of a development. As such, if an authority is set on developing an area, it could still do so regardless of the consequences on drainage. Narrower definition These latest SuDS requirements are the result of twists and turns of government policy, numerous consultations and delays. With April's announce- ment the government has chosen to adopt a far narrower definition of SuDS than the one generally accepted as best practice. Water quantity and flood mitigation are referred to, but water quality, amenity and biodiversity are given far less prominence. Despite its obvious short- comings, the CPSA's members welcome the introduction of SuDS as part of a range of drainage solutions to help protect people and property from the risk of flooding. As manufacturers of dependable SuDS components, including flood control, attenuation and underground storage systems, CPSA members are able to work with designers and installers to provide precast concrete SuDS solutions that offer excellent whole life value. Stuart Crisp is business development director at the Concrete Pipelines System Association. Hard SuDS include proprietary engineered precast concrete soakaways, attenuation tanks and treatment chambers News+

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