SUDS knowledge is key

When sustainable drainage specialist Polypipe WMS arranged a seminar on SUDS, the strong turnout was rewarded with rich insight from the expert speakers. Steed Webzell listened in.

In Britain it can rain a lot. In urban areas, dispersing this surface water to avoid flooding has always proven a costly, laborious and largely unsustainable chore. Sewers, gullies, grilles, are all at risk of blockage and require regular maintenance, repair and ultimately replacement, at great cost and in terms of time and disruption.

Sustainable drainage systems for urban areas have for the past decade been growing in profile and potential. All of the expert speakers at the seminar stated full support for ‘green’ infrastructure – entirely natural sustainable drainage. The reality, however, particularly in urban areas that have been covered extensively in impermeable surfaces, is that ‘natural’ is not always possible.

As a result, emphasis shifts to proprietary, engineered sustainable drainage solutions, and this proved to be the focus for David Schofield, associate director at independent consulting firm, Arup, who was the first keynote speaker on stage. Setting the tone for the seminar, Schofield likened the SUDS (sustainable urban drainage systems) initiative and the issues surrounding it as a series of hand grenades being detonated within the construction industry.

“Even where it’s technically feasible to provide a porous surface, to be authentically sustainable it has to be protected from future development,” said Schofield. “For drainage to be sustainable it must meet the needs of the present without compromising the ability of future generations to meet their own needs.”

As the best example he had seen of SUDS in action, Schofield highlighted a British Water focus group trip to Portland, Oregon, where an extensive network of roadside features and curb extensions called the ‘green stretch’ has been transformed in a showcase for sustainable drainage. So pleased are the residents with the results, that many of the areas have been readily adopted.

“As a group we learnt that empowerment and education for the general public were the key facilitators for implementation of sustainable drainage. If we want the sustainable drainage ‘dream’ to be realised all parties have to engage in consultation.”

He highlighted green roof technology as sustainable drainage potential unrealised, particularly as plant bioremediation has the ability to improve surface water quality. Pointers were also made to advanced technologies such as Polypipe’s Storm X4 treatment filter, which is capable of cleaning surface water run-off from roofs, car parks and roads.

But ultimately there remains concern about ongoing ownership of sustainable drainage systems, which is “one of the biggest challenges we have to overcome”.

Think tank

Steve Wilson, technical director at consultant design company EPG, talked about the structural design of modular/geocellular drainage tanks, which are proving increasingly popular as stormwater attenuation vessels and rainwater reuse systems underneath car parks, landscaping areas, distribution yards and minor estate roads.

“The trick is to ensure they are designed and installed correctly,” said Wilson. “These are plastic structures that must be specified correctly with regard to load capacity and ground conditions. Failure to do so can lead to collapse, which is why comprehensive testing is advisable to identify the worst case performance conditions for the tank.

“Collapses remain relatively isolated incidents but they attract media attention and this will only serve to reduce take-up from the water industry. Knowledge is increasing but care is still needed.”

Footing the bill

Presenting the impact of the (draft) Floods and Water Management Bill (FWMB) on local authorities, designers and engineers was Richard Ashley, professor of urban water at the University of Sheffield.

Now at the committee stage in the House of Lords, the FWMB intends to provide better, more comprehensive management of flood risk for people, homes and businesses. So is this the answer to everything?

“Well, it’s a welcome attempt to move from a process to an outcome perspective…but there are many problems,” Professor Ashley said.

Not least among them will be resources for the SUDS Approval Body and responsibilities in what will be a complex chain of command.

Ashley asked the 160-strong audience who they thought should shoulder the

responsibility for SUDS. The majority of hands were raised for local authorities, with water companies polling less and others such as the Environment Agency fewer still. The point is that SUDS inherently introduces yet more layers of bureaucracy, which when combined with an inability to work across regime boundaries and a lack of funding/staff resources, is a major concern.

Without doubt there is an awful lot going on at the same time. Aside from the SUDS initiative there is the WRc’s work on the costs and benefits to water utilities resulting from the proposed FWMB, as well as its CP329 project on the specification and maintenance of geocellular SUDS storage systems. Ofwat has a project on sustainable drainage, while DCWW has a surface water management strategy and UU is running pilot projects on retrofits.

From a technology perspective, Ashley conceded there are some clever ideas being rolled out. The Dutch for instance continue to push ahead with their ‘floating houses’ scheme. By the end of 2001, there will be more than 700 such dwellings in the Netherlands.

“The use of Formpave permeable block paving, which collects and filters stormwater for later use such as for geothermal heating or cooling, is another great idea,” he said, “as is the use of Polypipe storm cells and giant soakaways. Then there is increased adoption of blue roofs, which represent a good solution for densely developed urban landscapes with flat roofs.”

These are all strong ideas but capacity remains an issue. Additional capacity is needed for the requirements of: the FWMB (SUDS adoption); the flood risk regulations; national indicators on flood risk management, climate change and local biodiversity; the Pitt review; local development frameworks; and multi-agency management plans.

“It is no wonder our legislators are in a mess,” said Ashley. “The situation we are in is complex and for the first time in history we cannot build our way out of it. The regimes and their approach to dealing with the many challenges we face are not fit for purpose. Any sensible person would throw it all away and start again!

“Delivering sustainability requires change in governance not tinkering with a few regulations,” he continued. “The aftermath of the FWMB will need to ensure conditions are there to support the required transitions and regime transformation”.

Stepping stones

Engineered SUDS solutions, particularly source control pavement solutions and design considerations, provided the focus for Phil Tomlinson, SUDS manager at construction sector specialist, Aggregate Industries. As a primary SUDS technique, source control means controlling run off where it hits the ground.

Tomlinson talked about pervious pavement concepts along with infiltration and attenuation, as well as the various types of pervious paving materials such as gravel areas, grass-grid solid blocks, porous asphalt/concrete and concrete block permeable paving.

Among the case studies presented of source control SUDS in action was the Longstanton park & ride hub for Cambridgeshire County Council’s guided bus route. The main contractor for the project was BAM Nuttall, with SUDS design and engineering provided by EPG, Parsons Brinkerhoff and Arup. The project was to provide an 18,100m2 hard landscaped run off catchment.

Design parameters included a 100-year storm return period (+20% for climate change), a high water table and an allowable discharge of 10l/s.

“The solution comprised: permeable concrete block paving; modular, shallow, high strength attenuation units; open graded aggregate; oil separation, retention and treatment textiles; and collection and silt/oil separation/treatment channels,” said Tomlinson.

“This approach provided a minimum of two phases of effluent control at source, along with the elimination of deep end-of line petrol/oil separators. Construction outside of the water table and shallow storage tanks avoid deep excavation.”

Tomlinson’s presentation concluded a highly interesting event that provided insight into the vast subject of SUDS. Time is short and one thing is certain: all knowledge is valuable.

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