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"Sustainable Urban Drainage" is very much an issue...

"Sustainable Urban Drainage" is very much an issue of the day for planners and developers. For 30 years now we've been extolling the virtues of using self-draining paving layers as part of a wider stormwater strategy and so we're naturally pleased to see this shift towards planned environmental engineering. A key aim with "SUDS" is to mitigate and control surface water by the use of naturally percolating pavement surfaces. Our own preference has always been to seek a solution that will enhance but not radically shift the balance of nature. To achieve this we have long recommended that a "cross-site" uniform rate of percolation is sought, with a slight modification to the percolation rate to create a lag time between initial surcharge and eventual re-charge. In this way clay substrates still gain sufficient controlled moisture to prevent dying and cracking. Within a car park construction this can generally be achieved within the envelope of paving layer and sub-base, further enhancement can however be gained by installing an underlying drainage blanket layer consisting of low fines aggregate in a perforated geo-textile wrap. As part of our further commitment to the environment we encourage the use of re-cycled aggreagates for this layer - that need only be 100-150mm thick. This type of design contrasts with a relatively new concept of constructing underground "detention" tanks, to store the water in one location before controlled release either to ground or the main drainage network. Opinion seems divided amongst engineers as to whether this is a beneficial to stormwater management or detrimental to the natural hydrology of a site particularly where from elsewhere ground water is drawn towards the tanks by natural seepage. Whilst GRASSCRETE is an ideal paving partner for either system we are nevertheless conscious that we are seeking at all times to benefit the environment. With this in mind we would welcome your views and experiences of "SUDS" projects.

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