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SUDS solutions from Marley Plumbing & Drainage
The sudden heavy downpours experienced this year increased the incidence of flash floods, leaving everyone aware of the fact that good drainage is vital. Drainage issues stem from the period when construction and development across the UK was ‘sealing’ the ground surface with large areas of carparking, retail and industrial parks, new schools and hospitals, and large areas of new residential development. This was bad news for water companies and those in the path of potential floods. Areas of permeable land where rainwater could soak away decreased where land was being developed, and stormwater from hard paving and roofs moving directly into rivers and sewers increased the risk of flooding downstream, depletion of ground water and aquifers and potential pollution issues.
As a result of this, the Environment Agency, planning guidance and Building Regulations all now include advice, requirements and ultimately legislation for the management of stormwater, to keep rainwater on site longer, to slow down run off and to use drainage systems that allow storage, reuse and discharge at the point of origin. As a whole, these systems are now well known as sustainable urban drainage systems – SUDS.
SUDS can be divided into two types – above and below ground. Above ground types include channels, basins and ponds. Below ground options are attenuation – temporary storage before water is allowed to drain slowly into the watercourse or sewer, infiltration – allowing the water to permeate into the ground, and otherwise known as soakaway, and recycling – filtering and storing rainwater for use in non-potable outlets such as toilet flushing and garden irrigation. This final option is known as rainwater harvesting, and is a solution that could, with sufficient takeup, help to complete the circle in a drought crisis. Rainwater harvesting is a solution which seems so immediately beneficial and without shortcomings that it is hard to see why such systems have not been adopted sooner and on a more widespread basis.
By creatively employing the technology developed for stormwater attenuation and infiltration, rainwater harvesting systems are available which are flexible and capable of serving the largest development. Enlightened specifiers are beginning to see rainwater harvesting as part of the total SUDS package for all types of development.
This acceptability is evidenced by utility companies now offering rebates on water bills to those homes where rainwater harvesting is in use; elsewhere the Government is looking at an enhanced capital allowance scheme for businesses installing enhanced water technologies. While the environmental benefit must be an influencing factor in
the decision to install a system, the cost benefit will be seen by anyone with a water meter. Though not all residential properties are metered, it seems likely that the use of meters will become more widespread over the next decade.
The design of modular stormwater storage chambers is the catalyst allowing a dramatic change in the design of rainwater recycling systems. These types of modular chambers offer great versatility, being only 10kg each in weight yet exceptionally strong. Many chambers use columns of extruded polypropylene honeycomb structure, which can offer up to 96% usable volume or void.
Unlike a tank-based system, a modular rainwater harvesting system can combine infiltration, or soakaway, with recycling, thereby alleviating the twin issues of water shortage and flooding. The other great advantage of a modular system is its flexibility; any size and combination of storage or infiltration unit can be constructed, just as long as room is allowed for the central pumping riser.
The new modular systems offer huge benefits over the old, large tank rainwater harvesting options. A low cost water recycling system can be constructed from separate components consisting of an inlet chamber, filter unit, submersible pump unit and base unit combined with storage chambers to form a central filtering and pumping riser. An impermeable membrane is used to form a storage tank of a suitable size for the intended usage. For most domestic houses, depending on regional rainfall frequency and intensity, this would be a minimum size in plan of 1.8m wide and 2.4m long, to form a storage tank volume of 4.3m3, with a 2.2m3 volume mounted above for infiltration of excess water into the surrounding soil.
Simple to install, flexible through modularity, robust and durable, stormwater management systems are now elegant and simple solutions to a pressing need.
Fiona Bashford writes on behalf of Marley Plumbing and Drainage.
