Drains and water usage - the hot topic of conversation

Not so long ago, politics and religion were the main topics of conversation around the dinner table. Today, it is drains and water usage. And to help developers and builders make the right decisions, British Water has produced
a guidance document. We take a look.

It used to be so simple, water would come out of our taps and disappear down our drains. Now, drainage has become an unlikely hot topic of dinner table conversation all over Britain. With droughts, floods, climate change warnings and hosepipe bans, what happens to our water has suddenly started to grab headlines and the public attention.

After a summer when, for the first time, many of us have had to re-design our gardens with cactus and lavender, we are now facing a winter of flood warnings. It seems the dire predictions of global warming are finally becoming a reality.

A report by The Co-operative Bank and Friends of the Earth and based on research by the Tyndall Centre for Climate Change Research, warns that the Government has only four years in which to implement a major new programme of action to cut carbon emissions if the UK is to play its part in keeping global temperatures below danger levels.

In preparation for the global warming phenomenon and the fact that fresh water has, until now, been a cheap commodity, a group of experts from the British Water Sustainable Drainage Systems Focus Group, has been working with regulators to produce a timely guidance document to help developers, planners, builders and contractors make the right decisions when installing proprietary sustainable drainage systems and components.

The British Water Focus Group has consulted organisations throughout the industry in compiling the document that provides general guidance and comparative information on the criteria that should be assessed, when considering which is the best SUDS system for the proposed site.

It puts the needs of the environment at the top of the agenda whenever development is being considered for small, large, residential, industrial or commercial projects.

"The effect of drainage on the environment only becomes of major interest when the systems don't work", says Dr Ian Pallett, technical director of British Water, which is the major trade association for the supply chain with members from all sectors of the water and wastewater industry.

" We're beginning to see the problems that droughts, floods and other extreme weather can cause, and the indications are that it's going to get worse," he adds.

Conveying flow
To help them in their research and to ensure that all possible options are researched, the group has this year been on a Global Watch Mission to the US, travelling thousands of miles to examine methods used in the States to maximise sustainable drainage. A similar mission is now being planned for Europe.

The best practice document the Focus Group has produced covers the four main areas of proprietary SUDS solutions - infiltration, flow control, storage/attenuation and treatment. It lists the kind of products available and assesses how well they perform in particular situations, using headings such as adoptability, reliability, and ease of commissioning. It does not recommend or endorse any particular manufacturer's product.

"It's vital that anyone who's involved in development in any way makes sure they know what the options are and this document, which is free to download, will help them," says Pallett. "There's already quite a lot of advice available on soft SUDS solutions, such as swales, ponds and infiltration trenches, but we wanted to help people find the most appropriate equipment when they need proprietary SUDS."

The guidelines outline the Regulations that are already in place, working from the expectation that a drainage system should be adequate. The word " adequate" means that there should be a method of conveying the flow via a suitable network to a suitable outfall; blockages and leaks should be minimised; and the system should have sufficient capacity, be well ventilated and provide drainage from roofs or paved areas to a suitably designed drainage system.

The Regulations also expect that rainwater should only be discharged into a sewer as a last resort and discharges into the ground should be distributed in such a way that foundations of structures are not threatened.

Pallett comments: "We need to be sure that anyone working on drainage for any kind of development, large or small, is aware of the need to consider the local environment. The equipment that's right for a small suburban housing estate is unlikely to suit a large rural industrial development.

"Alongside the information that's already available, this document should help people reach the right decision."

In the Infiltration guidelines compiled by British Water's Focus Group, the emphasis is on protecting the environment which means using infiltration devices as the first option for stormwater with a watercourse as a second option and a sewer as an undesirable alternative.

The infiltration devices for stormwater considered include geocellular systems, perforated pipes, permeable surfaces and soakaways.

But infiltration systems have their limitations and are only effective in certain circumstances, for example where they do not put groundwater quality or ground stability at risk. Infiltration, the guidelines suggest, should not be used where run-off is likely to be heavily contaminated and the environmental information about the area needs to be consulted at the very earliest design stages.

It is also advised that, to allow access for maintenance and to prevent structural damage, land use above and below the system may have to be restricted.

The guidelines give a complete table of systems, applications and their limitations so that designers, engineers and surveyors can see at a glance which system would suit each project.

Regular inspection
The Storage and Attenuation section demonstrates how attenuation storage will allow the control of peak storm water.

It outlines each of the possible options and the factors such as drainage depth, site layout, site usage and space available, which will influence the final decision.
The emphasis here is on knowing what the site conditions are as well as the discharge licences that are stipulated by the regulating body.

The pros and cons of a storage and attenuation system are outlined and again each type is categorised with its strengths and weaknesses.

Alex Stephenson, chair of the British Water Focus Group and Stormwater director of Hydro International, says: " This is the first time the industry has had such a comprehensive guide to what works and what doesn't in all circumstances. To put this document together, we've consulted all the main regulatory bodies as well as practising members in the industry to make sure we've got the best guidelines."

The Flow Control section covers methods of retaining or diverting flows within surface water networks to create various forms of storage and to control outflow rates in accordance with the requirements of the environmental regulators. One of the problems with controlling flows is the fact that they involve a physical restriction or barrier of some sort, leading to potential problems with blockages.

The guidelines suggest ways to avoid problems in this area and highlight the methods that are less likely to block.

Everything from float operated to vortex flow controls are covered.

The final section deals with treatment and dealing with pollutants. To get the best out of these systems, the guidelines stress the importance of maintenance and regular inspection to prevent build up of sediments in SUDS and avoid contamination of streams, rivers, ground water and other surface water.

One of the next targets for the group will be to concentrate on the future requirements of the Water Framework Directive and the likely effect that will have on dealing with pollutants into watercourses and groundwater.

Stephenson says: "With heavy fines for pollution - £20,000 and above in some instances - installers and designers now have to take great care when choosing a system that will have a trouble-free lifespan for each particular site. To be able to understand what works best and where, will save the industry a great deal of hassle and cost, but the main consideration has to be for the environment.

"We are dealing with dirty as well as clean water and we need to be certain that neither of them will cause problems for people or wildlife. British Water was set up to raise standards in the industry. With well researched documents like this we feel this focus group is helping to achieve that."

Guidance to proprietary drainage systems and components is available to download free from http://www.britishwater.co.uk/html/publications.html

Sustainable Drainage Systems: a mission to the USA A DTI Global Watch Mission Seminar was held in London on July 2006, when as well as a series of presentations from the mission participants and a panel discussion, a full written report of the missions findings was also launched.

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