Driveways: Drainage After The Floods

Between the memory of the country-wide floods in the first few months of 2014, and the prospect of still greater deluges yet to come promised by the newly published report from the Intergovernmental Panel on Climate Change (IPCC), drainage has, surely, never been more firmly in our minds.

There’s nothing new about the idea of sustainable urban drainage systems – or SUDS as they are most commonly known – or the potential value they can have in helping mitigate flooding risks. With SUDS forming a central part of the government’s strategy to deal with floods, new legislation over recent years has helped propel the whole concept firmly into centre-stage, and the changes to rules on general permitted development have altered the way we view hard-standing altogether. Today, no one is unaware of the importance of good drainage – and the driveway is where it all begins.

Anti flood options for driveways

Fortunately, providing a driveway that complies with the all the rules, acts effectively to manage excessive surface run-off and still looks aesthetically pleasing, does not have to be too much of a challenge – not least because a small industry has grown up around the issue, and options are plentiful.

Broadly speaking, there are two main approaches to ensuring a flood resistant drive, based on what you do with the water. In effect you can either manage the flow, collecting it and directing it to where you want it, or you can adopt a approach that allows it to percolate naturally into the ground.

Flow management

One of the key benefits of the flow management approach is that it enables ‘traditional’ impermeable driveway materials to be incorporated into the design, thus retaining the look of the old, while attaining the enhanced performance requirements of the new.

Depending on the site, this might entail adding suitable driveway channels or soak-aways to materials such as asphalt, or even simply arranging the levels so that surrounding flowerbeds take the flow – assuming they are large enough and have sufficient capacity, of course.

As with all drainage projects, it is important to get appropriate professional advice where necessary to avoid costly mistakes, and the nature of the soil or sub-soil will also need to be investigated to make sure that it can properly soak up the volume of water anticipated.

Percolation rather than divertion

For some applications, particularly where low-level flooding and/or high rainfall build-up is a known risk, percolation can be preferable to diverting the water, and a range of proprietary permeable driveway products are available which can give an attractive, and SUDS-compliant, finish to the job.

Some of these resemble traditional paving blocks, but feature a high-tech wicking design that pulls water between them and down into a special base layer, and then ultimately into the soil. Another type that is becoming increasingly popular combines interlocking concrete blocks and specially selected grasses to provide a greener (in every sense of the word) option, which may be particularly appropriate for more rural driveways.

Engineered percolation systems of this kind are, however, only as good as their foundations, which can typically involve a 20 – 30 cm base layer of coarse crushed stone, topped off with a 5cm laying course of finely crushed stone. On that basis, it’s probably fair to say that this is definitely one for the professionals, unless, of course, you are an incredibly competent individual yourself!

Making effective drainage a priority

One thing that last winter’s depressing catalogue of storms and downpours have made very clear is that while effective drainage cannot protect against floods entirely, it can make a big difference when it comes to the severity of the effect of flooding, particularly in relatively densely built-up areas.

Quite aside from the demands of planning legislation and building regulations, the potential impact that driveways and parking areas can have on surface water management in their immediate vicinity has to be viewed as a major priority from the outset, if local drainage is not to suffer.

With much of the historical hard-standing areas of the UK’s older properties ill-equipped by modern standards to deal with excess run-off, and accelerated new-build widely accepted as essential to deal with the nation’s growing population, driveway drainage looks set to remain a hot topic for some time.

Getting it right has to be good news for home-owners, particularly those in high flood-risk areas, and for household insurance premiums everywhere!

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